JSCE 1997(b)

preface

Página Página 1 de 1

PREFACE The Concrete Committee of the Japan Society of Civil Engineers set up a "Research Committee on Continuous Fiber Reinforcing Materials (CFRM)" in 1989, chaired by Prof. H.Okamura. The fee for the resear research ch works works was offere offered d by the Associ Associati ation on of Compos Composite ite Materi Materials als using using Continuous Fiber for Concrete Reinforcement (CCC). The research committee's work involved various aspects of CFRM, e.g. review of research works and actual applications; study on how to design structures, to deal with durability problems and on the test methods. The committee work was compiled as a state-of-the art report on "Application of Continuous Fiber Reinforcing Materials to Concrete Structures" and published in Japanese in the journal, Concrete Library, No. 72 in 1992. Another aim of the committee was to offer a chance to committee members to study about the material by their own way in order to collect ideas on the fundamental designing methods. The work done by the committee members was published together with the research work done by other researchers in the proceedings of the Symposium on Application of CFRM on Concrete Structures (Concrete Engineering Series 1) in April 1992. A part of the work related to the designing method and the state-of-the-art report was translated into English and published as "State-of-the-Art Report on Continuous Fiber Reinforcing Materials" (Concrete Engineering Series 3) in October 1993. For CFRM to be widely used in the field of concrete, it is necessary to have a set of guidelines for practical design and construction methods together with the standard test methods and specifications. The Second Research Committee on CFRM was thus set up by JSCE Concrete Committee, entrusted by CCC and the Advanced Composite Cable Club (ACC), to prepare such guidelines. The committee spent three years from November 1993 to October 1995 to come up with its recommendations. The following four working groups were set up within the committee: (1) Design method (Chairman: Prof. Y. Kakuta) (2) Construction methods (Chairman: Prof. T. Tsuji) (3) Specifications (Chairman: Prof. T. Uomoto) (4) Standard test methods (Chairman: Prof. H. Seki). The work done by the committee was published in Japanese in Concrete Library, No. 88, in 1996. The article includes recommendations for design and construction, specifications, standard test methods and necessary data for using CFRM. This "Recommendation for Design and Construction of Concrete Structures using Continuous Fiber Reinforcing Materials" (Concrete Engineering Series 23) is a translated version of the above-mentioned report which was written in Japanese. I hope that people throughout the world who use CFRM as reinforcement for concrete structures will find the information contained in this book useful. September 1, 1997 Atsuhiko Machida

Chairman The Second Research Committee on CFRM, JSCE

http://www.jsce.or.jp/committee/concrete/e/newsletter/newsletter01/recommendation/

09/12/2010

Committee members


Committee members Chairman

Atsuhiko Machida

Secretary

Taketo Uomoto

Members

Taisuke Akimoto

Tadayoshi Ishibashi

Takashi Idemitsu

Tamon Ueda

Hidetaka Umehara

Nobuaki Ohtsuki

Kazumasa Ozawa

Yoshio Kakauta

Hirotaka Kawano

Masayuki Kanda

Ryoichi Sato

Hiroshi Shima

Hiroshi Seki

Yukikazu Tsuji

Seiichi Tottori

Makoto Nakasu

Junichiro Niwa

Atsushi Hattori

Tadakatsu Hara

Tetsuo Harada

Takeshi Higai

Tsutomu Fukute

Mitsuyasu Mashima

Kyuichi Maruyama

Takehiko Maruyama

Ayaho Miyamoto

Hiroshi Mutsuyoshi

Keitetsu Rokugo

Hajime Wakui

Yoshifumi Maeda

Committee members from trustees Hikaru Akiyama

Yoshiaki Imai

Shinichiro Kumagai

Tamio Tamura

Kenzo Sekijima

Hiromitsu Taniguchi

Seijiro Koga

Design working group members Chairman

Yoshio Kakauta

Secretary

Hiroshi Mutsuyoshi

Hiroshi Shima

Members

Taisuke Akimoto

Tamon Ueda

Masayuki Kanda

Seiichi Tottori

Junichiro Niwa

Takeshi Higai

Kyuichi Maruyama

Sadatoshi Ohno

Hikaru Akiyama

Yoshiaki Imai

Yoshiaki Hironaka

Nobuyuki Murata

Construction working group members Chairman

Yukikazu Tsuji

Secretary

Hidetaka Umehara

Members

Tadayoshi Ishibashi

Takashi Idemitsu

Hirotaka Kawano


09/12/2010

Committee members


Committee members Chairman

Atsuhiko Machida

Secretary

Taketo Uomoto

Members

Taisuke Akimoto

Tadayoshi Ishibashi

Takashi Idemitsu

Tamon Ueda

Hidetaka Umehara

Nobuaki Ohtsuki

Kazumasa Ozawa

Yoshio Kakauta

Hirotaka Kawano

Masayuki Kanda

Ryoichi Sato

Hiroshi Shima

Hiroshi Seki

Yukikazu Tsuji

Seiichi Tottori

Makoto Nakasu

Junichiro Niwa

Atsushi Hattori

Tadakatsu Hara

Tetsuo Harada

Takeshi Higai

Tsutomu Fukute

Mitsuyasu Mashima

Kyuichi Maruyama

Takehiko Maruyama

Ayaho Miyamoto

Hiroshi Mutsuyoshi

Keitetsu Rokugo

Hajime Wakui

Yoshifumi Maeda

Committee members from trustees Hikaru Akiyama

Yoshiaki Imai

Shinichiro Kumagai

Tamio Tamura

Kenzo Sekijima

Hiromitsu Taniguchi

Seijiro Koga

Design working group members Chairman

Yoshio Kakauta

Secretary

Hiroshi Mutsuyoshi

Hiroshi Shima

Members

Taisuke Akimoto

Tamon Ueda

Masayuki Kanda

Seiichi Tottori

Junichiro Niwa

Takeshi Higai

Kyuichi Maruyama

Sadatoshi Ohno

Hikaru Akiyama

Yoshiaki Imai

Yoshiaki Hironaka

Nobuyuki Murata

Construction working group members Chairman

Yukikazu Tsuji

Secretary

Hidetaka Umehara

Members

Tadayoshi Ishibashi

Takashi Idemitsu

Hirotaka Kawano


09/12/2010

Committee members


Makoto Nakasu

Atsushi Hattori

Tetsuo Harada

Tsutomu Fukute

Takehiko Maruyama

Keitetsu Rokugo

Masafumi Imai

Hideo Ogino

Yukihiro Kawamoto

Shinichiro Kumagai

Seijiro Koga

Hiromitsu Taniguchi

Test method working group members Chairman

Hiroshi Seki

Secretary

Nobuaki Ohtsuki

Members

Taketo Uomoto

Kazumasa Ozawa

Ryoichi Sato

Tadakatsu Hara

Tetsuo Harada

Tatsunori Makizumi

Mitsuyasu Mashima

Atsuhiko Machida

Ayaho Miyamoto

Hajime Wakui

Takeshi Enomoto

Masaya Kamiyoshi

Hajime Saitoh

Atsushi Tsunoda

Kenzo Sekijima

Kensuke Tanigi

Tamio Tamura

Toshihiko Yoshizumi

Quality specifications working group members Chairman

Taketo Uomoto

Members

Atsushi Hattori

Tadakatsu Hara

Kyuichi Maruyama

Takehiko Maruyama

Hajime Wakui

Kenzo Sekijima

Yoshiaki Hironaka

Tamio Tamura


09/12/2010

CHAPTER 1: GENERAL 1.1 SCOPE (1) This Design Recommendation gives general requirements for design of concrete structures using continuous fiber reinforcing materials. Subjects not covered in this Recommendation shall comply with the JSCE "Standard Specification for Design and Construction of Concrete Structures (Design)" (hereinafter referred as the "JSCE Standard Specification (Design)"). (2) Continuous fiber reinforcing materials shall in principle conform to JSCE-E 131 "Quality Specifications for Continuous Fiber Reinforcing Materials".

[COMMENT]: (1) "Concrete structures using continuous fiber reinforcing materials" include structures where continuous fiber reinforcing materials is used together with steel reinforcement or prestressing steel. Chapter and section numbers given in this Design Recommendation refer to the JSCE Standard Specification (Design), 1996 edition.

1.2 DEFINITIONS The following terms are defined for general use in this Design Recommendation: Reinforcing materials: Materials used to reinforce concrete. These include steel and continuous fiber

reinforcing materials. Continuous fiber : General term for continuous fibers used to reinforce concrete. These include

carbon fibers, Aramid fibers and glass fibers. Fiber binding materials: Adhesive used to consolidate continuous fibers. These are mostly plastics

such as epoxy resin or vinylester resin. Continuous fiber reinforcing materials (CFRM) : General term for unidirectional reinforcement

formed from continuous fibers impregnated with a fiber binding material, then hardened and molded, in the form of bundled or woven continuous fibers, used for reinforcing the concrete. Capacity of CFRM : Maximum load that a continuous fiber reinforcing material can sustain. Strength of CFRM : Value obtained by dividing the capacity of continuous fiber reinforcing material

by the nominal cross-sectional area. Characteristic value of capacity of CFRM : Value for the capacity of continuous fiber reinforcing

material below which the percentage of test results obtained using a given test method is guaranteed not to exceed a given figure, allowing for variations in test results.

-1-

Specified value of capacity of CFRM : (as distinct from the characteristic value of capacity of

CFRM:) Capacity value for continuous fiber reinforcing material determined in accordance with structural specifications other than this Recommendation, or other regulations. Guaranteed capacity of CFRM : Guaranteed capacity in accordance with JSCE-E 131 "Quality

Specifications for Continuous Fiber Reinforcing Materials" Design capacity of CFRM : Value obtained by dividing the characteristic value of capacity of

continuous fiber reinforcing material by the material coefficient. Characteristic value of ultimate strain of CFRM : Strain corresponding to the characteristic value of

tensile capacity of continuous fiber reinforcing material. Design ultimate strain of CFRM : Value obtained by dividing the characteristic value of ultimate

strain of continuous fiber reinforcing material by the material coefficient. Tensile rigidity of CFRM: Slope of the tensile force-strain curve for continuous fiber reinforcing

material, when this curve is assumed to be linear. Young’s modulus of CFRM : Value obtained by dividing the tensile rigidity of continuous fiber

reinforcing material by the nominal cross-sectional area. Nominal cross-sectional area of CFRM : Value obtained by dividing the volume of continuous fiber

reinforcing material by the length. Bent portion of CFRM: Portion of continuous fiber reinforcing material set in a curved shape by

hardening with a fiber binding material while the continuous fibers are bent. Curved placement of CFRM: Placement of straight continuous fiber reinforcing material in a curved

layout. Creep failure: Failure due to progressive loss of tensile capacity over time, when continuous fiber

reinforcing material is subjected to a continuous static tensile load. Creep failure capacity: Capacity at the time of creep failure. Flexural compressive failure: Form of failure in members subjected to flexure, whereby the

compressed section of concrete fails before the main continuous fiber reinforcing material breaks. Fiber rupture flexural failure: Form of failure in members subjected to flexure, whereby the main

continuous fiber reinforcing material breaks before the failure of the compressed section of concrete. Fiber rupture shear failure: Form of shear failure in members subject to shear forces, due to

breaking of continuous fiber reinforcing material used as shear reinforcement.

-2-

[COMMENTS]: Definitions of shear reinforcement, lateral ties, hoop reinforcement, spiral reinforcement, and tendons follow the JSCE Standard Specification (Design), where "steel reinforcement or prestressing steel" shall be read simply as "reinforcing materials". Since the nominal cross-sectional area of CFRM is obtained by dividing the volume of the CFRM by the length, and volume generally includes sectional area which does not contribute to the strength of the reinforcement, the strength and Young’s modulus of CFRM obtained by division by the nominal cross-sectional area are not identical with the value for the continuous fiber itself.

1.3 NOTATION Notation used in this Design Recommendation with reference to structural design is as follows: A f

: Cross-sectional area of CFRM placed in tensile zone

A fc c f

: Cross-sectional area of CFRM necessary based on calculation : Center-to-center distance of CFRM

E 0

: Standard Young’s modulus (200 kN/mm 2 = Young’s modulus of steel)

E f

: Young’s modulus of CFRM used in verification of service limit state : Young’s modulus of CFRM used as tendons

E fp E fu E w

: Young’s modulus of CFRM used in verification of ultimate limit state : Young’s modulus of shear reinforcement or transverse torsional reinforcement

F fu f fb

: Tensile capacity of CFRM : Strength of bent portion of CFRM

f fc

: Creep failure strength of CFRM

f fpu f fu

: Tensile strength of CFRM used as tendons : Tensile strength of CFRM

f w

: Strength of shear reinforcement or transverse torsion reinforcement

ε fspd

: Material coefficient of CFRM : Design value of strain at ultimate limit state for spiral reinforcement

ε fu

: Ultimate strain of CFRM

ε fwd

: Design value of strain at ultimate limit state for shear reinforcement

σ fe

σ fpe

: Increase in reinforcement stress due to design load, used in verification of crack width : Increase in reinforcement stress due to permanent load : Increase in tendon stress due to design load, used in verification of crack width

σ fpp

: Increase in tendon stress due to permanent load

γ mf

σ fp

[COMMENT]: Subscript f refers to CFRM.

-3-

CHAPTER 2: DESIGN BASICS 2.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), section 2.1.

2.2 DESIGN SERVICE LIFE It shall be in accordance with JSCE Standard Specification (Design), section 2.2.

2.3 DESIGN PREREQUISITE It is assumed for the purposes of design based on this Recommendation that construction on site will be carried out appropriately at all times.

[COMMENT]: The basic stance relating to structural design is given here. It is assumed that construction is carried out following the intentions of the designer. Appropriate construction refers to construction carried out according to the Construction Recommendation.

2.4 DESIGN PRINCIPLES It shall be in accordance with JSCE Standard Specification (Design), section 2.4.

2.5 CALCULATION OF SECTIONAL FORCE AND CAPACITY It shall be in accordance with JSCE Standard Specification (Design), section 2.5.

2.6 SAFETY FACTORS It shall be in accordance with JSCE Standard Specification (Design), section 2.6. Safety factors relating to CFRM shall be determined according to each limit state.

[COMMENT]: Standard values for safety factors are shown in Table C 2.6.1, below.

-4-

Table C 2.6.1: Standard safety factors

Material factor γ m Concrete

CFRM

Member

Structural

Load

Structural

factor

analysis

factor

factor

Steel

factor

γc

γ mf

γ s

γ b

γ a

γ f

γ i

Ultimate limit state

1.3* or 1.5

1.15** to 1.3

1.0 or 1.05

1.15 to 1.3

1.0

1.0 to 1.2

1.0 to 1.2

Serviceability

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Fatigue limit

1.3*

1.15**

1.05

1.0

1.0

1.0

1.0

state

or

to

limit state

1.5

1.3

to

to

1.1

1.1

*

1.3 where characteristic value of concrete compressive strength f' ck is less then 50 N/mm 2

**

1.15 for CFRM with carbon or Aramid fibers

2.7 CORRECTION FACTOR It shall be in accordance with JSCE Standard Specification (Design), section 2.7.

2.8 DESIGN CALCULATIONS It shall be in accordance with JSCE Standard Specification (Design), section 2.8.

2.9 DRAWINGS Design drawings shall give structural and reinforcement details, showing clearly the following: (1) Design conditions (2) Details of bent portion of CFRM (3) Cover of reinforcing material in all parts of the structure (4) Locations of construction joints assumed in design (5) Detail drawings of zones with intertwining reinforcing materials, sheaths, anchor bolts etc. (6) Nominal diameter of sheaths, if used (7) Locations and dimensions of major chamfers

[COMMENTS]: Design drawings should be considered the only means of transmitting the intentions of the designer to the constructor. Clear information must therefore be given regarding the conditions on which the design is based. These include the standard design strength of concrete, slump, maximum size of coarse aggregate, standards for reinforcing materials and minimum compressive strength of concrete at which prestressing may be carried out in post-tensioning prestressed concrete.

-5-

The capacity of bent portion of CFRM is generally lower than that of straight lengths, but the degree of loss depends heavily on the geometry and dimensions of the bent portion. Therefore, details of the bent portion must be given clearly. Concrete cover and concrete quality are also important factors in relation to the durability of concrete structures, and the realization of a durable concrete structure depends on these factors being examined thoroughly at the design stage. In order to transmit all of these details to the constructor, concrete cover in all parts should be clearly indicated in the design drawings. Detail drawings of zones with intertwining reinforcing materials, sheaths, anchor bolts etc. should be prepared, and the properties of concrete at these zones be verified.

-6-

CHAPTER 3: DESIGN VALUES FOR MATERIALS 3.1 GENERAL (1) The quality of concrete and reinforcing materials are expressed, in addition to compressive strength and tensile strength, in terms of material characteristics such as strength characteristics, Young’s modulus, deformation characteristics, thermal characteristics, durability, water tightness etc., according to the design requirements. In the case of strength and deformation characteristics, loading velocity may have to be taken into consideration. (2) The characteristic values given for material strength and ultimate strain of CFRM are minimum values the majority of test results are guaranteed to exceed, allowing for variations in test values. (3) Values for the design strength of materials and the design ultimate strain of CFRM shall be obtained by dividing the relevant characteristic values by the material coefficients.

[COMMENT]: (2) It is recognized that the tensile strengths obtained from tensile tests using the same CFRM show greater variation than does steel. The amount of variation in tensile strength differs depending on the type, geometry etc. of the continuous fibers and the fiber binding material, and variation is found even for the same CFRM depending on the length of the test piece and the anchoring method used during testing. The characteristic values for the material strength of CFRM are therefore minimum values the majority of test results are guaranteed to exceed.

3.2 CONCRETE It shall be in accordance with JSCE Standard Specification (Design), 3.2.

3.3 STEEL It shall be in accordance with JSCE Standard Specification (Design), 3.3.

3.4 CFRM 3.4.1 Capacity (1) Characteristic values for tensile capacity of CFRM shall be determined on the basis of tensile tests. Tensile tests shall be conducted in accordance with "Test Method for Tensile Properties of Continuous Fiber Reinforced Materials (JSCE-E 531-1995)". (2) For materials conforming to "Quality Specifications for Continuous Fiber Reinforced Materials (JSCE-E 131)", the tensile capacity may be taken to be identical to the guaranteed capacity.

-7-

(3) Where CFRM is to be shaped by bent portion or curved placement, or where CFRM are to be subjected to diagonal tensile forces, the capacity shall be determined based on the results of suitable tests. (4) The design strength of bent portion of CFRM shall normally be calculated as follows: f fbd

=

where f fbk =

f fbk / γ mfb

(3.4.1)

r  005 + 0.3 f fuk  .  h

(3.4.2)

If the right side of the above equation resolves to a value greater than f fuk , f fbk shall be taken as f fuk . f fbk

: characteristic value of strength of bent portion

f fuk r

: characteristic value of unconfined tensile strength : internal radius of bend

h

: cross-sectional height of CFRM : can generally be taken as 1.3

γ mfb

(5) The design strength of CFRM to be used in a curved placement may be obtained by subtracting the elastic bending stress of the curved portion from the design strength of the straight portion. (6) The compressive capacity and shear capacity of CFRM may be ignored for design purposes. (7) The material coefficient γ mf of CFRM shall be determined allowing for the quantity and deviation of test data, possible damage to CFRM during transportation and construction, differences in material characteristics between test pieces and actual structures, the effects of material characteristics on the limit state, service temperatures, environmental conditions etc. and 1.3.

γ mf

may generally be set between 1.15

[COMMENTS]: (1) CFRM are compound materials formed from continuous fibers and fiber binding materials. When forces act on CFRM, therefore, at the microscopic level the local stresses acting on individual fibers and the binding materials will vary. When considering CFRM as reinforcing material in concrete, however, it is simpler to treat the CFRM as a monolithic material. The strength of CFRM is thus taken to be the capacity of the entire section (at maximum load). If the nominal-cross sectional area of the CFRM is known, strength (maximum load / nominal cross-sectional area) may be used instead of capacity. (3) If CFRM are to be used in bent portion or in curved placement, or if the CFRM are subjected to diagonal tensile forces such that diagonal cracks occur, the tensile capacity falls below the unconfined tensile capacity of the straight CFRM. In bent portion or curved placement, the rate of reduction has been confirmed experimentally to be dependent on the ratio of the radius of curvature of the bent portion or curved placement and the diameter of the CFRM, on the angle of the working tensile force if diagonal tensile forces are present, etc. In such cases, the capacity shall be determined on the basis of the results of suitable tests. When CFRM are to be used in curved placement, the capacity shall

-8-

normally be determined according to "Test Method for Flexural Tensile Properties of Continuous Fiber Reinforced Materials (JSCE-E 532-1995)". (4) The strength of bent portion varies greatly even for the same type of fiber, depending on the bending technique, type of resin used etc., therefore the strength of the bent portion will generally be determined on the basis of suitable tests. From comparisons with existing test data, the strength of bent portion has been found to be derivable as a function of the internal radius of the bent section, from Eq. (3.4.1). The regression equation in Fig. C 3.4.1 gives the averages of all test data. The design equation Eq. (3.4.2), based on this regression formula, gives an adequate margin of safety.

Fig. C 3.4.1: Strength of bent portion

(5) CFRM generally have a lower elastic modulus than steel reinforcement, so they can be bent and arranged within the elastic region. At small bending radii, though, the strength of the bent portion is reduced by the effects of elastic bending stress and bearing stress. The policy adopted here has been to approximate these effects by subtracting the elastic bending stress from the strength of the straight portion. (6) CFRM consist of extremely fine collection of fibers, and therefore have extremely low compressive and shear capacity when used as reinforcing material. In normal designs, therefore, compressive and shear capacity of CFRM will be ignored.

3.4.2 Fatigue capacity (1) The characteristic values for fatigue capacity of CFRM shall be determined based on fatigue capacity derived from fatigue tests conducted allowing for the type, size, anchoring, intensity and frequency of working stress, environmental conditions etc. (2) The material coefficient

γ mf relating

to the design fatigue capacity of CFRM is determined allowing

for the quantity and deviation of fatigue test data, service temperatures, environmental conditions etc. If the CFRM are liable to suffer damage during transportation and construction, the effects of such damage shall be allowed for in

γ mf . γ mf may

generally be set between 1.15 and 1.3.

-9-

[COMMENTS]: (1) The quantity of research findings relating to the fatigue in CFRM is still inadequate, and further experimental investigations are required. When CFRM is used as tendons in prestressed concrete, if cracking is not allowed, the variable stresses will be small and the effects of fatigue will be negligible, but if cracking is allowed, fatigue must be verified in the same way as if prestress was not present. The fatigue capacity of CFRM requires the fatigue characteristics not only of the CFRM, but also of the anchorages to be clarified. As loss of capacity due to secondary stresses in particular, is significant in CFRM, the fatigue characteristics including those of the anchorages are important. The static capacity of bent portion is known to be considerably lower than that of straight portions for certain types of CFRM. The fatigue capacity of bent portion is still lower than the static capacity of bent portion. Where slipping of CFRM occurs at intersections with cracks etc., fatigue strength is known to be reduced even in conventional steel reinforcement, but the fatigue capacity in CFRM is reduced still further because the static capacity is also reduced. This reduction of fatigue capacity occurs at the intersections with shear cracks of both shear and tensile reinforcement.

3.4.3 Tensile force-strain relationship (1) The tensile force-strain curve of CFRM used in verification of ultimate limit state may be assumed to follow the model shown in Fig. 3.4.1, in which a straight line connects tensile capacity obtained from tests and the corresponding ultimate strain points with the origin. (2) The tensile force-strain curve used in verification of the serviceability limit state of CFRM may be assumed to follow the model shown in Fig. 3.4.2, in which a straight line connects the tensile rigidity calculated in accordance with "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials (JSCE-E 531-1995)". (3) The tensile force-strain curve used in verification of the fatigue limit state of CFRM shall be the same as that used in verification of the serviceability limit state.

Fig. 3.4.1 Tensile force-strain curve used for the design of ultimate limit state

- 10 -

Fig. 3.4.2 Tensile force-strain curve used for the design of serviceability limit state

[COMMENTS]: (1) The tensile force-strain curves for CFRM vary slightly depending on the type of fiber, but in general the tangential rigidity varies with the load level as shown in Fig. 3.4.2, therefore models have been set up for each limit state. For the tensile force-strain curve used in verification of ultimate limit state, test for tensile strength according to JSCE-E 531 is carried out and the bearing characteristics of capacity are calculated according to JSCE-E 131. The design capacity is obtained by dividing this by the material coefficient, and the design ultimate strain is obtained by dividing this by the nominal cross sectional area and Young’s modulus. (2) The tensile force-strain curve used in verification of the serviceability limit state is the tensile force-strain curve obtained according to JSCE-E 531, assumed to be a straight line through the origin having the same gradient as the line connecting the points corresponding to tensile capacity of 20% and 60%.

3.4.4 Coefficient of thermal expansion The coefficient of thermal expansion of CFRM shall generally be as given in Table 3.4.1. Table 3.4.1 Thermal expansion coefficient of CFRM

Type of CFRM

Thermal expansion coefficient ( × 10-6/°C)

Aramid fiber

-6

Carbon fiber

0

Glass fiber

10

[COMMENT]: The coefficients of thermal expansion of CFRM in the axial direction vary depending on the type of fiber, within the ranges shown in Table C 3.4.1. The values given in Table C 3.4.1 for glass fiber are the same as those for concrete. Conservative values are given for other types of fiber, where the coefficients of thermal expansion are different from those of concrete.

- 11 -

Table C 3.4.1 Thermal expansion coefficient of CFRM

Type of CFRM

Thermal expansion coefficient ( × 10-6/ oC )

Aramid fiber

-2 ~ -6

Carbon fiber Glass fiber

0.6 ~ 1 9 ~ 10

3.4.5 Relaxation rate (1) Relaxation rate for CFRM shall generally be as calculated according to "Test Method for LongTerm Relaxation of Continuous Fiber Reinforcing Materials (JSCE-E 534-1995)". (2) The apparent relaxation rate to be used in calculating prestress loss shall be based on the relaxation rate of the CFRM, allowing for the effects of drying shrinkage and creep of the concrete.

[COMMENTS]: (1) As little data is available relating to relaxation rate of CFRM, and long-term data (more than 1000 hours) is especially lacking, it has been decided to use the values obtained according to JSCE-E 534. The relaxation rate corresponding to a service life of 100 years is taken to be the value for 1 million hours, extrapolated from the relaxation values for times in excess of 1000 hours. Where the service life of the structure is determined in advance, the relaxation value corresponding to the predetermined service life may be applied. (2) Little experimental data is currently available on which to base an equation for the calculation of apparent relaxation rate. This may therefore be estimated on the basis of test data, or if necessary the net relaxation rate may be used.

3.4.6 Creep failure capacity The creep failure capacity of CFRM shall be calculated according to "Test Method for Creep Failure of Continuous Fiber Reinforcing Materials (JSCE-E 533-1995)".

[COMMENT]: CFRM subjected to sustained stresses for long periods may undergo rupture (creep failure) at less than the static bearing capacity. This creep failure capacity varies depending on the fiber type. Tensioning must therefore be carried out allowing for the creep failure capacity when CFRM is used as tendons. For design purposes, the creep failure capacity is that corresponding to a design service life of 100 years and the creep failure capacity based on the 1 million hour creep failure - limit load ratio given in JSCE-E 533 shall be applied. Where the service life of the structure is determined in advance, the creep failure capacity corresponding to the predetermined service life may be estimated from the 1 million hour creep failure - limit load ratio.

- 12 -

CHAPTER 4: LOADS 4.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 4.1.

4.2 CHARACTERISTICS VALUES OF LOADS It shall be in accordance with JSCE Standard Specification (Design), 4.2.

4.3 LOAD FACTORS It shall be in accordance with JSCE Standard Specifications (Design), 4.3.

4.4 LOAD TYPES (1) Loads other than seismic loads shall be in accordance with JSCE Standard Specification (Design), 4.4. (2) Seismic loads shall be in accordance with JSCE Standard Specifications (Seismic Design). The effects of plastic deformation of structures shall normally not be considered.

[COMMENT]: When steel is used as reinforcing material, allowance for the effects of plastic deformation of structures due to yielding of steel members is permitted, but as yielding does not take place when CFRM is used, structures cannot be expected to undergo plastic deformation unless special measures are taken. For this reason, plastic deformation of structures shall normally not be considered. Where steel reinforcement is used in conjunction with CFRM, seismic behavior must be verified on the basis of a suitable evaluation of the plastic deformation capacity of the structure, either according to test results or to non-linear analysis based on a reliable theory.

- 13 -

CHAPTER 5: STRUCTURAL ANALYSIS 5.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 5.1.

5.2 CALCULATION OF SECTIONAL FORCES IN ULTIMATE LIMIT STATE It shall be in accordance with JSCE Standard Specification (Design), 5.2. Redistribution of bending moment due to plastic deformation of structures shall not be considered in general.

[COMMENT]: Allowance for redistribution of bending moment due to plastic deformation of structures is normally permitted in statically indeterminate structures incorporating continuous beams, rigid frames, continuous slabs etc. However, as yielding does not take place when CFRM is used, unless special constraining reinforcement is placed in the concrete, the structure cannot be expected to yield. For this reason, redistribution of bending moments due to plastic deformation of structures shall not be considered in general. If the rate of rigidity loss due to the appearance of cracking varies greatly between different members, the effects of redistribution of bending moments due to cracking sometimes cannot be ignored. In such cases, redistribution of bending moments due to cracking must be allowed for in calculation of section forces.

5.3 CALCULATION OF SECTIONAL SERVICEABILITY LIMIT STATE

FORCES

AND

DEFORMATION

It shall be in accordance with JSCE Standard Specification (Design), 5.3.

5.4 CALCULATION OF SECTIONAL FORCES IN FATIGUE LIMIT STATE It shall be in accordance with JSCE Standard Specification (Design), 5.4.

- 14 -

IN

CHAPTER 6: ULTIMATE LIMIT STATE 6.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 6.1. The collapse mechanism in statically indeterminate structures shall not be considered.

[COMMENT]: As yielding does not take place in CFRM, the collapse mechanism due to the formation of plastic hinges shall generally not be considered. The effects of steel reinforcement on member capacity when CFRM is used in conjunction with steel reinforcement may be calculated according to JSCE Standard Specification (Design), 6.2 to 6.4.

6.2 SAFETY VERIFICATION OF BENDING MOMENT AND AXIAL FORCE 6.2.1 Design capacity of member cross-section (1) In members subjected to axial compressive force, the upper limit of axial compressive capacity N' oud oud shall be calculated according to Eq. (6.2.1) when ties are used, and according to Eq. (6.2.1) or Eq. (6.2.2) whichever that gives the larger result when spiral reinforcement is used. N' oud Ac / γb oud = 0.85 f’ cd cd

(6.2.1)

N' oud Ae +2.5 E spε fspd A spe) / γb oud = (0.85 f’ cd cd

(6.2.2)

where Ac

: cross-sectional area of concrete

Ae

: cross-sectional area of concrete enclosed by spiral reinforcement : equivalent cross-sectional area of spiral reinforcement (=πd sp A sp/ s) s)

A spe d sp A sp

: diameter of concrete section enclosed by spiral reinforcement : cross-sectional area of spiral reinforcement

s f' cd cd

: pitch of spiral reinforcement : design compressive strength of concrete

E sp

: Young’s modulus of spiral reinforcement ( E fu)

ε fspd

: design value for strain of spiral reinforcement in ultimate limit state, may generally be taken as 2000 × 10 -6. If the design strength f fbd is less than E than E spε fspd when the spiral reinforcement is regarded as a bent portion, E portion, E spε fspd shall be substituted for f for f fbd .

γb

: Member factor, generally taken to be 1.3

(2) When the bending moment and the design capacity of member cross-sections are calculated according to the direction of section force for unit width of member sections or members, calculations shall be performed on the basis of assumptions (i) to (iii) given below. (i) Fiber strain is proportional to the distance from the neutral axis. (ii) Tensile stress of concrete is ignored. (iii) The tensile force - strain curve of the CFRM follows 3.4.3.

- 15 -

(3) For fiber rupture flexural failure, the capacity when any reinforcement reaches design ultimate strain ε fud as shown in Fig. 6.2.1 is taken to be the design capacity of the member cross-sections. The member factor

γb may generally be taken as 1.15 to 1.3.

Fig. 6.2.1 Strain condition at fiber rupture flexural failure in members with multi-layer reinforcement

(4) For flexural compression failure, the compressive stress distribution in the concrete may be assumed to be identical to the rectangular compressive stress distribution (equivalent stress block) given in JSCE Standard Specification (Design), 6.2.1(3). The member factor γb may generally be taken as 1.3. (5) The design capacity of a member cross-section subjected to combined biaxial bending moment and axial forces shall be calculated according to (2) to (4) explained above. (6) When the effect of axial forces is negligible, the cross-sectional capacity may be calculated as for a flexural member. Axial forces may be taken to be negligible when e/h ≥ 10, where h is section height and eccentricity e is the ratio of design flexural moment M d to design axial compressive force N' d .

[COMMENTS]: Particularly when high ductility is required, measures such as combining CFRM with steel reinforcement, confinement of compression zone concrete etc., have to be implemented. (1) As the compressive strength of CFRM is lower than the tensile strength and subject to significant variation, the effects of compressive strength are to be ignored for the purposes of calculation of axial compressive capacity N' oud . The effects of using CFRM for spiral reinforcement are allowed for in Eq (6.2.2). The design value

ε fspd for the strain of spiral reinforcement at ultimate limit state has been set at 2000 × 10-6, allowing for the fact that in the equation for axial compression capacity when steel reinforcement is used, the steel is assumed to yield on the basis of test results. If the design strength when spiral reinforcement is regarded as a bent portion f fbd is lower than E spε fspd , the latter may be substituted. (3) As there is no yielding and no plastic region when CFRM is used, rupture begins from reinforcing materials when the strain of the reinforcement reaches the ultimate strain. The first rupturing of the reinforcing material is thus generally simultaneous with the ultimate state of the member, and capacity is calculated from the strain distribution obtained assuming plane sections remain plane. In a member with steel reinforcement arranged in multiple layers, stress may be evaluated from the position of the center of gravity of the steel, but for CFRM, as Fig. 6.2.1 illustrates, fiber rupture flexural failure takes place when the outermost reinforcement reaches the ultimate strain. If different types of CFRM are

- 16 -

used within the same section, or if bonded and unbonded reinforcing material is used together, these circumstances must be allowed for in calculating the capacity. (4) In flexural compression failure, it is possible to calculate capacity in the same way as for steel, therefore calculation of capacity using the equivalent stress block method is allowed here.

6.2.2 Structural detail (1) Minimum axial reinforcement (i) In concrete members reinforced with CFRM where axial forces are dominant, the quantity of axial reinforcement shall be not less than 0.8( E 0/ E fu)% of the calculated minimum cross-sectional area of the concrete, where E 0 is reference Young’s modulus (=200 kN/mm 2), and E fu is Young’s modulus of axial reinforcement. The "calculated minimum cross-sectional area of the concrete" here refers to the minimum cross-sectional area of concrete required for axial support only. Where the section is larger than the minimum required section, the amount of axial reinforcement should preferably be in excess of 0.1( E 0/ E fu)% of the concrete cross-sectional area. (ii) The ratio of tensile reinforcement in beam members where the effects of bending moment are dominant shall generally be not less than (35 f tk / f fuk )% or 0.2%, whichever is the greater. For T-cross sections, the amount of axial tensile reinforcement shall be not les s than 1.5 times as great as the above value, relative to the effective cross-sectional area of the concrete. In this, f tk is the characteristic value of the tensile strength of the concrete, and f fuk is the characteristic value of the tensile strength of the tensile reinforcement. The "effective cross-sectional area of the concrete" here refers to the effective depth of the section d multiplied by the web width bw. (2) Maximum axial reinforcement In concrete members where axial forces are dominant, the amount of axial reinforcement shall generally be not greater than 6( E 0/ E fu)% of the cross-sectional area of the concrete.

[COMMENTS]: (1) (i) The compressive strength of CFRM can be ignored for the purpose of calculating axial compressive capacity, but in order to ensure axial rigidity, a minimum amount of axial reinforcement has been specified, as for steel reinforcement. Where the member cross section is larger than the calculated minimum cross-sectional area of the concrete, while a minimum axial reinforcement is required from the point of view of cracking, as CFRM is not liable to corrosion, the requirements given here have been relaxed slightly as compared to those for steel reinforcement. Where CFRM is used in conjunction with steel, however, the value of (steel quantity + ( E fu/ E 0) · CFRM quantity) must be not less than 0.15% of the cross-sectional area of the concrete. (ii) Where the ratio of tensile reinforcement is extremely low, the reinforcement ruptures as soon as cracking appears, inducing a state of brittle failure. The minimum amount of reinforcement is prescribed in order to avoid this. Allowing for the size effect of the member, the minimum tensile reinforcement ratio may be either (35 k 1 f tk / f fuk )% or 0.2%, whichever is the greater. k 1 is obtained from Eq. (C 6.2.1).

- 17 -

k1

= 0.6 / (h 1/ 3 )

(C 6.2.1)

where h is total member depth (m), provided that 0.4

≤

k 1 ≤ 1.0.

6.3 SAFETY VERIFICATION OF SHEAR FORCES 6.3.1 General It shall be in accordance with JSCE Standard Specifications (Design), 6.3.1.

6.3.2 Design shear forces of beam members It shall be in accordance with JSCE Standard Specifications (Design), 6.3.2.

6.3.3 Design shear capacity of beam members (1) Design shear capacity V ud is obtained from Eq. (6.3.1), provided that when bent-up reinforcement and stirrups are used together for shear reinforcement, the stirrups bear not less than 50% of shear force required to be borne by the shear reinforcement. V ud = V cd + V sd + V ped

(6.3.1)

where V cd

: design shear capacity of beam members not used in shear reinforcement, obtained

from Eq. (6.3.2). V cd = βd ⋅ β p ⋅ β n ⋅ f vcd ⋅ bw ⋅ d / γ b

(6.3.2)

where

f vcd

= 0.23 f 'cd

2 (N/mm ), provided that f vcd ≤ 0.72 N/mm2

(6.3.3)

βd = 4 1 / d (d :m); if βd > 1.5 then βd = 1.5 β p = 3 100 pw E fu / E 0 ; if β p > 1.5 then β p = 1.5 βn = 1 + M 0/ M d ; (if N' d ≥

βn = 2 1 + 2 M 0/ M d (if N' d < 0); if βn < 0 then βn = 0 N' d M d M 0

0); if βn > 2 then

: design axial compressive force : design bending moment : bending moment required to cancel out stresses set up by axial forces in the tensioned edge, relative to design bending moment M d

E fu E 0 bw

: Young’s modulus of tensile reinforcement : reference Young’s modulus (=200 kN/mm 2) : width of web

d : effective depth pw = A f /(bwd ) A f

: cross-sectional area of tensile reinforcement

f' cd

: design compressive strength of concrete, in units of N/mm2 : generally = 1.3

γb

- 18 -

V sd V sd

: design shear capacity borne by shear reinforcement, obtained from Eq. (6.3.4) (6.3.4) = Aw E wε fwd (sin α s + cosα s ) / ss + Apwσ pw (sinα p + cosα p ) / s p z / γ b

[

]

Aw

: total cross-sectional area of shear reinforcement in section s s

E w

: Young’s modulus of shear reinforcement (= E fu)

ε fwd

: design value of shear reinforcement strain in ultimate limit state, obtained from Eq. (6.3.5). Where E wε fwd is greater than the design value for the strength of the bent portion f fbd , f fbd is substituted for E wε fwd . f fbd may be obtained from Eq. (3.4.1).

ε fwd = α s

f 'mcd

  σ '   −4 1 + 2 N   × 10 pweb E w   f 'mcd   pw E fu

(6.3.5)

s s

: angle formed by shear reinforcement and member axis : spacing of shear reinforcement

pweb

: Aw/(bw· s s)

A pw

: total cross-sectional area of shear reinforcement tendons in section s p : effective tensile stress of shear reinforcement

σ pw σ pw = σwpe + E fpwε fwd ≤ f fpud σwpe : effective tensile stress of shear reinforcement tendons E fpw f fpud

α p s p z

: Young’s modulus of shear reinforcement : design tensile strength of shear reinforcement : angle formed by shear reinforcement and member axis : spacing of shear reinforcement : distance from point of action of compressive stress resultant force, generally d / 1.15

σ' N

: average axial compressive stress σ' N = ( N' d + P ed ) / A g if σ' N > 0.4 f' mcd then σ' N = 0.4 f' mcd

P ed A g f' mcd

: effective tensile force in axial tendons : total cross-sectional area : design compressive strength of concrete allowing for size effect (N/mm2)

 h  f 'mcd =   0.3  f' cd h

γb V ped

−1/ 10

⋅ f 'cd

: design compressive strength of concrete, in N/mm2 : member depth (m) : generally = 1.15

: component of effective tensile force of axial tendons parallel to shear force, obtained from Eq. (6.3.6)

V ped = P ed sinα p /γb α p : angle formed by shear reinforcement and member axis : generally = 1.15 γb

(6.3.6)

(2) When beam members are supported directly, V ud need not be investigated for the zone from the support face to one-half of the depth h of the members. In this zone, shear reinforcement more than the

- 19 -

minimum required shall be placed in the cross section from the support face to h/2. In members of non-uniform section, the depth at the support face may be adopted as the member depth; parts of a haunch where the gradient is less than 1:3 shall be considered to be effective. (3) The design diagonal compressive capacity V wcd of web concrete to shear force shall be obtained from Eq. (6.3.7). Vwcd = f wcd ⋅bw ⋅ d / γ b

(6.3.7)

where

f wcd

2 ); provided that f wcd ≤ = 125 . f 'cd (N/mm γb = generally = 1.3

7.8 N/mm2

(4) Web width of members (i) Where the diameter of a single duct in prestressed concrete members is equal to or greater than 1/8 of the web width, the web width assumed in Eq. (6.3.2) shall be smaller than the actual web width bw. In such a case, the web width may generally be reduced by the total of the diameters of the ducts φ arranged in that section, giving bw - 1/2Σφ. (ii) For members with web widths varying in the direction of member depth, other than those with circular sections, the minimum width bw within the range of effective depth d shall be adopted. For members with multiple webs, bw shall be the total width of all webs. For solid or hollow circular sections, web width bw shall be either the length of one side of a square with the equivalent area, or as the total width of webs of square boxes having the same area. In these cases, the area of axial tensile reinforcement A f shall be the cross-sectional area of reinforcement in 1/4 (90°) of the cross section of the tensioned side. The effective depth d shall be either the distance from the compression edge of the square or box of equivalent area to the centroid of the reinforcement, accounted for as A f . These definitions of axial tensile reinforcement area shall not apply in calculation of flexural capacity.

Fig. 6.3.1 Definitions of b and d for various cross-sections w

[COMMENTS]: (1) The design shear force V ud , as shown in Eq. (6.3.1), is given as the sum of the components carried by the concrete V cd and by the shear reinforcement V sd , except that the components (V ped ) of effective tensile force in the axial reinforcement parallel to the shear force is ignored. Previous studies indicate that the shear capacity of beam members with CFRM used for tensile reinforcement but without shear reinforcement can generally be evaluated by taking into account the axial rigidity of the tensile reinforcement. V cd is thus calculated according to the equation used for steel, allowing for the ratio of the Young’s modulus of CFRM to that of steel.

- 20 -

The strain

ε fwd of shear reinforcement at the

ultimate limit state is affected by concrete strength, the

rigidity of tensile and shear reinforcement, and axial compression force. These functions are given by Eq. (6.3.5). Eq. (6.3.5) is derived from the most recent findings of research on the design shear capacity of beam members using CFRM, shown below. These findings offer a more accurate method than the conventional one for estimating shear stress, by incorporating a more realistic shear resistance mechanism. This method may be followed in estimating the ultimate shear capacity. The shear capacity obtained by the method given below is generally greater than that obtained from Eq. (6.3.1). The method below is greatly simplified, for instance by conservatively ignoring the effect of the shear span-to-depth ratio on shear capacity, but in some instances it will give a lower shear capacity than Eq. (6.3.1), for example when the main reinforcement has high rigidity. Design shear capacity when shear reinforcement does not break is calculated as follows: V ud = V cd + V sd

(C 6.3.1)

where V cd = design shear force carried by concrete, obtained from Eq. (C 6.3.2) V cd = V czd + V aid

(C 6.3.2)

where V czd

: design shear force carried by concrete in compression zone, obtained from Eq. (C 6.3.3) (C 6.3.3) Vczd = βf 'mcd xebw / γ b

V aid

: design shear force carried by concrete in diagonal cracking zone, obtained from Eq. (C 6.3.4) Vaid

= β P β pE f 'mcd 1/ 3 (h − xe )bw / γ b

(C 6.3.4)

V sd = shear capacity carried by shear reinforcement, obtained from Eq. (C 6.3.5) V sd = Aw E wε fwd (h − x e )bw / (tan θ cr s s ) / γ b (C 6.3.5) xe

: depth of concrete compression zone at ultimate, obtained from Eq. (C 6.3.6) 0.7     ' σ xe = [1 − 0.8( pweb E fw ) − 0.2 1 +  N     f 'mcd  

ε fwd

: strain in shear reinforcement at ultimate limit state, obtained from Eq. (C 6.3.7)

ε fwd = 0.0001 θcr

(C 6.3.6)

x

f ' mcd

  σ '   1 + 2  N   pweb E w   f 'mcd   pw E fu

(C 6.3.7)

: angle of diagonal cracking, obtained from Eq. (C 6.3.8)

  σ '  0.7  θcr = 451 −  N     f 'mcd   0.7  σ ' N  β = 0.2   f 'mcd  σ' β P = 1 − 5 N ; if βP < 0 then β P = 0

(C 6.3.8)

f 'mcd

 p E + 10 pweb E w  β pE = 0.24 w fu + 0.66 ; if βpE > 0.40 then β pE = 0.40 5000k  

- 21 -

 σ '  k = 1 −  N   f 'mcd  f' mcd

0.1

: design compressive strength of concrete, allowing for size effect (N/mm2)

 h  f 'mcd =   0.3 

−1/ 10

⋅ f 'cd

f' cd bw

: design compressive strength of concrete (N/mm2) : web width

d

: effective depth

h

: beam height (m)

A f Aw

: cross-sectional area of tension reinforcement (mm2) : total cross-sectional area of shear reinforcement in zone s s

pw = A f /(bwd ) pweb = Aw /(bw s s) E fu : Young’s modulus of tension reinforcement (N/mm 2) E w

: Young’s modulus of shear reinforcement (N/mm 2)

2 σ ' N = ( N' d + P ed )/ A g (N/mm ); if σ ' N > 0.4 f ' mcd then σ ' N = 0.4 f ' mcd

N' d

: design axial compression force

P ed

: effective tensile force of axial reinforcement

A g

: cross-sectional area of entire section : spacing of shear reinforcement

s s x

γb

: position of neutral axis according to elastic theory, ignoring tension section : generally = 1.3

Design shear capacity when shear reinforcement breaks by fiber rupture is calculated as follows: V ud = V c0 - βm(V c0 - V czd ) + βmV aid + βmV sd

(C 6.3.9)

where V c0

: load at which diagonal cracking occurs, obtained from Eq. (C 6.3.10) V c0 =β0βd f’ cd x0bw /γb + β P 0β pE 0βd f’ cd 1/3(h- x0)bw/γb

(C 6.3.10)

V czd

: design shear force carried by concrete in compression zone; may be obtained from Eq. (C 6.3.3)

V aid

: design shear force carried by concrete in diagonal cracking zone; may be obtained from Eq. (C 6.3.4)

V sd

: design shear force carried by shear reinforcement; may be obtained from Eq. (C

x0

: depth of compression zone in concrete at onset of diagonal cracking, obtained from

6.3.5) Eq. (C 6.3.11)

  σ '  0.7  x0 = 1 +  N   x   f 'cd   0.7  σ ' N  β0 = 0.14   f 'cd  βd = 4 1000 / d ; if βd > 1.5 then βd = 1.5 σ' β P 0 = 1 − 5 N ; if β P 0 < 0 then β P 0 = 0 f 'cd

- 22 -

(C 6.3.11)

 pw E fu  β pE 0 = 017 .  + 0.66 ; if β pE 0 > 0.28 then β pE 0 = 0.28  5000k   σ '  k = 1 −  N   f 'cd  βm = f ud

0.7

f ud E wε fud : design tensile strength of shear reinforcement, taken as equivalent to design strength of bent portion f fbd , where f fbd may be obtained from Eq. (3.4.1)

Design shear capacity V ud , as shown in Eq. (C 6.3.1), is expressed as the sum of the components carried by concrete V cd and by shear reinforcement V sd . For each of these components, the effects of the Young’s modulus of the tendons are evaluated as the rigidity obtained by multiplying the reinforcement ratio by the Young’s modulus of the reinforcing material. The shear force carried by the concrete in the compression zone increases as the axial compression force increases. This is expressed by Eq. (C 6.3.3). The mode of failure of the beam varies depending on the rigidity (reinforcement ratio

× Young’s

modulus) of the main reinforcement and the shear reinforcement. That is, as the rigidity of the main reinforcement and the shear reinforcement increases, the failure mode shifts from diagonal tensile failure to shear compressive failure. β pE in Eq. (C 6.3.4) signifies that when the rigidity of the main reinforcement and the shear reinforcement is low and the beam undergoes diagonal tensile failure, the shear transmission stress of the diagonal cracking zone increases as the rigidity of the main reinforcement and the shear reinforcement increases. However, when the rigidity is high and the beam undergoes shear compressive failure, the shear transmission force of the concrete in the diagonal cracking zone remains constant regardless of the rigidity of the main reinforcement and the shear reinforcement (Fig. C 6.3.2).

Fig. C 6.3.2 Effect of rigidity of longitudinal and shear reinforcement on shear strength

The shear span-to-depth ratio also affects the mode of failure, although previous studies have confirmed that at shear span-to-depth ratios of 2 or more, if the reinforcement has low rigidity, diagonal tensile failure will occur. Where axial compressive force is present, the mode of failure shifts from diagonal tensile failure to shear compressive failure. Previous studies have confirmed that shear compressive failure occurs even at low reinforcement rigidity, and the term k in

- 23 -

β pE (Eq. C 6.3.4) is

included to allow for this effect. That is, the reference value ( pw E fu + 10 pweb E w = 5000) for the case where axial compressive force is not acting, decreases as the axial compressive force increases. The angle of diagonal cracking, i.e. the angle of the truss diagonals, becomes shallower as the axial compressive force increases. This is expressed in Eq. (C 6.3.8). Shear reinforcement is thought to fail if the stress in shear reinforcement at ultimate limit state E wε fwd is greater than the strength of the bent portion f fbd , obtained from Eq. (3.4.1). In this case, the design shear capacity V ud is obtained from Eq. (C 6.3.9). That is, stress in the shear reinforcement after the onset of diagonal cracking, and components V czd and V aid , are thought to vary linearly according to the acting shear force, and components V czd , V aid and V sd are reduced by a factor βm, obtained by dividing the failure strength of the shear reinforcement by the shear reinforcement stress E wε fud , calculated assuming non-failure of the shear reinforcement ( Fig. C 6.3.3).

Fig. C 6.3.3 Modeling of each component of shear capacity

The method given here for calculation of shear capacity is derived from dynamic models agreeing with empirical facts, such as that the angle of the main compressive stress within the concrete is not 45° even if the angle of shear cracking within the shear span is generally 45° relative to the member axis, and that the load stress of the concrete carried outside of the truss mechanism varies with the acting shear force, and its value is not equivalent to the shear capacity of members without shear reinforcement. Eq. (C 6.3.5) which follows this method gives the shear force carried by shear reinforcement straddling diagonal cracks; where axial forces are not present, the angle of diagonal cracking is 45°, and the expression approximates the equation given in the JSCE Standard Specification, and also Eq. (6.3.4) of the present Recommendation. The difference between the two equations is that Eq. (C 6.3.5) incorporates a term ( h- xe) expressing the depth of the diagonal cracking zone, whereas Eq. (6.3.4) incorporates a term z expressing the arm length of the truss. According to the model referred to above, shear forces other than those carried by the truss mechanism are expressed by V czd in Eq. (C 6.3.3), and this value generally varies with the acting shear force (cf. Fig. C 6.3.3). The sum of this term V czd and V aid , the shear force transmitted by the interlocking of the

aggregate in the diagonal cracking zone etc. (cf. Eq. (C 6.3.4)), is generally constant, corresponding closely with Eq. (6.3.2). (3) The width of diagonal cracking is thought to be wider when CFRM is used than when steel reinforcement is used. The compressive capacity and rigidity of concrete where cracking is present

- 24 -

decreases as the strain perpendicular to the cracks increases, therefore diagonal compressive failure capacity is thought to be lower than when steel reinforcement is used. This hypothesis is yet to be confirmed experimentally, however, and in the present specifications, diagonal compressive capacity of reinforced concrete beams is evaluated conservatively in Eq. (6.3.7).

6.3.4 Design punching shear capacity of planar members (1) When the loaded area is positioned far from free edges or openings, and the eccentricity of the load is small, the design punching shear capacity V pcd may be determined by Eq. (6.3.8). V pcd

= βd ⋅ β p ⋅ βr ⋅ f pcd ⋅ u pd / γ b

(6.3.8)

f pcd

= 0.2

(6.3.9)

where f ' cd (N/mm2); f pcd shall be ≤ 1.2 N/mm2

βd = 4 1 / d (d :m); if βd > 1.5 then βd = 1.5 β p = 3 100 pE fu / E 0 ; if β p > 1.5 then β p = 1.5 βr = 1 + 1/1(1+0.25 u/d ) f' cd

: design compressive strength of concrete (N/mm2)

u

: peripheral length of loaded area

E fu E 0

: Young’s modulus of tensile reinforcement : standard Young’s modulus (=200 kN/mm2)

u p

: peripheral length of the design cross-section at d /2 from the loaded area

d , p

: effective depth and reinforcement ratio, defined as the average values for the reinforcement in both directions.

γb

: generally = 1.3

(2) When the loaded area is located in the vicinity of free edges or openings in members, the reduction of the punching shear capacity shall be allowed for. (3) When loads are applied eccentrically to the loaded area, the effects of flexure and torsion shall be allowed for.

[COMMENT]: (1) As with the shear capacity of beam members without shear reinforcement, the punching shear capacity may generally be evaluated by allowing for the axial rigidity of the reinforcement. The Young’s modulus of the CFRM is therefore allowed for in the calculation of design punching shear capacity V pcd .

6.3.5 Structural details (1) In beam members, stirrups not less than 0.15( E 0/ E fu)% shall; be arranged over the entire member length, where E 0 is standard Young’s modulus (=200 kN/mm 2), and E fu is Young’s modulus of axial reinforcement. The spacing of the stirrups shall generally be not more than 1/2 of the effective depth of the member, and not more than 30 cm. This provision (1) need not be applied to planar members.

- 25 -

(2) Shear reinforcement equivalent to that required by calculation shall also be arranged in sections equivalent to the effective depth outside of the section where it is required. (3) The ends of stirrups and bent bars shall be adequately embedded in the concrete on the compressive side.

[COMMENT]: (1) When steel reinforcement is used, stirrups equivalent to not less than 0.15% of the concrete area are installed to prevent sudden failure due to the onset of diagonal cracking. Based on this provision, a minimum amount of stirrup of 0.15( E 0/ E fu)% is also imposed here for CFRM reinforcement. As most CFRM have low elasticity and small cross-sectional areas, the spacing requirements given here are slightly stricter than those for steel.

6.4 TORSION SAFETY 6.4.1 General (1) For structural members not significantly influenced by torsional moment, and those subjected to compatibility torsional moment, the torsional safety studies given in section 6.4 may be omitted. "Structural members not significantly influenced by torsional moment" here refers to members in which the ratio of the design torsional moment M td to the design pure torsional capacity M tcd , calculated according to 6.4.2 (members without torsional reinforcement), multiplied by structural factor γi, is less than 0.2 for all sections. (2) When the effects of design torsional reinforcement are not negligible, torsion reinforcement shall be arranged in accordance with 6.4.2.

6.4.2 Design torsional capacity (1) Torsional capacity in members without torsional reinforcement shall be in accordance with "JSCE Standard Specification (Design)", section 6.4.2. (2) Torsional capacity in members with torsional reinforcement shall be calculated according to appropriate methods.

[COMMENT]: (2) Studies of CFRM used for torsional reinforcement have not yet been adequately carried out. Design torsional capacity in members with torsional reinforcement must therefore be investigated experimentally and analytically based on reliable techniques.

- 26 -

CHAPTER 7: SERVICEABILITY LIMIT STATES

7.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 7.1.

7.2 CALCULATION OF STRESS AND STRAIN It shall be in accordance with JSCE Standard Specification (Design), 7.2, with the following assumptions made regarding CFRM: (i) CFRM is elastic body; (ii) The Young’s modulus of CFRM is determined according to 3.4.3(2).

7.3 STRESS LIMITATION It shall be in accordance with JSCE Standard Specification (Design), 7.3. The limitation of tensile stress in CFRM shall be determined by testing, according to the type of reinforcing material used.

[COMMENT]: Unlike reinforcing or prestressing steel, CFRM undergoes failure at less than their static strength when subjected to sustained stress for long periods (i.e. creep failure). Creep failure strength is to be tested according to JSCE-E 533 "Test Method for Creep Failure of Continuous Fiber Reinforcing Materials" based on the test results up to 1000 hours, extrapolating the creep failure strength at 1 million hours. The limitation of tensile stress in CFRM may generally be derived by multiplying the characteristic value of creep failure strength f fck by a reduction factor of 0.8, given that the creep failure strength varies significantly depending on the fiber type, and given als o that creep testing requires long periods of time. The limit value shall be not more than 70% of the characteristic value for tensile strength. Creep failure as a phenomenon properly belongs under investigation of ultimate limit state, although it is placed in this section on serviceability limit state owing to the nature of the loads studied. For this reason, a reduction factor is used instead of a material factor.

7.4 CRACKING 7.4.1 General (1) It shall be examined by an appropriate method that cracking in concrete does not impair the function, durability, appearances of the structures. (2) This clause shall be applied to the verification of cracking caused by flexural moment, shear force, - 27 -

torsional moment and axial force.

(3) Where the appearances of the structure is deemed important, the crack width on the concrete surface shall generally be kept within an allowable crack width considered acceptable for aesthetic considerations. Verification of cracking may be omitted for structures with particularly short service life, temporary structures, or structures where aesthetic considerations are not important. (4) Where watertightness is important, the verification of cracking shall be done according to JSCE Standard Specification (Design), 7.4.1(4). [COMMENTS]: (1) Unlike steel materials, CFRM is considered to be free from corrosion. Cracking in concrete structures, however, generally results in loss of watertightness, airtightness and other functions, deterioration of the concrete, excessive deformation, unattractive appearance etc. Cracking in concrete must therefore be examined according to appropriate methods, to ensure that t he functions, appearances of the structure are not impaired. (3), (4) Verification of serviceability limit state when the intended purpose of the structure dictate particular aesthetic requirements, watertightness and airtightness requirements shall if necessary be made on the basis of a maximum allowable crack width.

7.4.2 Allowable crack width (1) The allowable flexural crack width w a shall generally be determined based on the intended purpose of the structure, environmental conditions, member conditions etc. (2) Allowable crack widths set for aesthetic considerations may generally be set to not more than 0.5 mm, depending on the ambient environment of the structure. (3) Crack limitations and allowable crack widths set for considerations of watertightness shall be based on JSCE Standard Specification (Design), 7.4.2(3).

[COMMENTS]: (1) Allowable crack widths must be determined based on the intended purpose of the structure - function, relative importance, service life etc., the ambient environment and loading conditions, and also on member conditions such as the effects of axial force, covering, variation in crack widths etc. (2) As CFRM is generally considered to be non-corrosion, there is no necessity to set allowable crack widths out of consideration of corrosion. Excessive crack width, however, would impair the appearance of the structure, as well as having a negative psychological impact. Whether or not cracking is likely to occur should first be investigated, and if cracking to be allowed, an appropriate allowable cracking width should be set based on aesthetic considerations, depending on the type of structure, the distance of the structure from the eyes of the casual onlooker, etc. Generally speaking, where main reinforcement is not prestressed, if the CFRM has low rigidity, large crack width may occur even at low load levels. - 28 -

Where CFRM is used in conjunction with steel reinforcement, steel corrosion must also be considered in setting the allowable crack width, and in this case the allowable crack width is based on JSCE Standard Specification (Design), 7.4.2. Where steel reinforcement is not used, the maximum allowable crack width for members in public view has been set at not more than 0.5 mm.

7.4.3 Verification of flexural cracks (1) Verification of flexural cracks may be omitted where the tensile stress of the concrete due to flexural moment and axial forces is lower than the design tensile strength of the concrete considering size effect. (2) In the verification of flexural cracks shall be made, in general, the crack width w obtained from Eq. (7.4.1) shall be confirmed to be less than the allowable crack width wa.

w = k {4c + 0.7(c f

− φ )}σ fe

′ E f (or σ pe E fp ) + ε csd

(7.4.1)

where k = constant expressing the effects of bond characteristics and multiple placement of reinforcing materials; generally 1.0~1.3 c = concrete cover (mm) c f = center-to-center distance between reinforcing materials (mm)

φ = diameter of reinforcing materials (mm) ε' csd = compressive strain for evaluation of increment of crack width due to shrinkage and creep of concrete

σ' fe = stress increase in reinforcement E f = Young’s modulus of reinforcement

σ fpe = stress increase in tendons E fp = Young’s modulus of tendons (3) The reinforcement and tendons to be examined for flexural cracks shall generally be the tensile reinforcement nearest to the concrete surface. Stress and strain shall be obtained according to section 7.2 above.

[COMMENTS]: (1) Design tensile strength of concrete considering the size effect shall be according to Eq. (C 7.4.1) in the JSCE Standard Specification (Design). (2) Eq. (7.4.1) is the same as that used for calculation of crack widths in concrete members using conventional steel reinforcement. The width and spacing of flexural cracks is generally affected significantly by the bond between the reinforcement and the concrete. CFRM may be classified according to their method of manufacture and surface geometry as strand, braid, wound, machined, lattice etc., and each type is considered to have different bond characteristics. Previous studies have found that when the surface is treated to give bond characteristics similar to conventional deformed steel bars, the spacing of cracks in concrete members is almost identical to that when deformed steel bars are used. In cases such as this, crack width can be calculated according to Eq. (7.4.1). The bond properties of CFRM are generally between those of round steel bars and deformed steel bars. The value of k in Eq. (7.4.1) must therefore be determined appropriately for each CFRM type, although for CFRM which has - 29 -

been confirmed to have bond characteristics similar to those of deformed steel bars, a value of k = 1.0 may be adopted. The term ε' csd in Eq. (7.4.1) expresses the effects of concrete shrinkage and creep on crack widths, and must be determined on the basis of the surface configuration of the member, ambient environment, stress levels etc. Little basic data is available regarding ε' csd , and further research in this area is required, but on the basis of an overall consideration of existing crack width formulae etc., ε' csd can generally be taken to be = 150 × 10-6. When latticed CFRM is used, the lattice spacing also affects crack spacing; this effect is allowed for by calculating crack spacing l k , calculating the crack width according to the following eq.:

w = l k (σ fe / E f

+ ε ' csd )

(C 7.4.1)

The basic policy regarding control of crack widths is to keep the width of cracks on the concrete surface below the allowable crack width determined on the basis of structural conditions and the concrete cover, although for convenience of design, for normal members a limit is set on the increase of strain in the CFRM due to permanent loads, considered to have minimal effect on crack widths; t his provision allows the verification of crack widths in (2) to be omitted. Generally speaking, if either the strain increase in the reinforcement due to permanent loads

σ fp /E f , or the strain increase in the tendons σ fpp /E fp, is less than

500 × 10 , verification of crack width may be omitted. -6

(3) If CFRM is arranged in multiple layers, normally the stress used will be that of the tensile reinforcement closest to the concrete surface, although the effects on crack width of CFRM further inside the section may also be evaluated, if such effects have been determined experimentally to be present.

7.4.4 Verification of shear cracks It shall be in accordance with JSCE Standard Specification (Design), 7.4.5.

[COMMENT]: Verification of shear cracks is normally to be done according to JSCE Standard Specification (Design), 7.4.5, although this verification may be omitted where the strain increase in the shear reinforcement due to permanent loads is less than 500 × 10-6.

7.4.5 Verification of torsion cracks It shall be in accordance with JSCE Standard Specification (Design), 7.4.6.

[COMMENT]: Verification of torsion cracks is normally to be done according to JSCE Standard Specification (Design), 7.4.6, although this verification may be omitted where the strain increase in the torsional reinforcement due to permanent loads is less than 500 × 10-6.

7.4.6 Structural Details - 30 -

It shall be in accordance with JSCE Standard Specification (Design), 7.4.7.

7.5 DISPLACEMENT AND DEFORMATION 7.5.1 General It shall be in accordance with JSCE Standard Specification (Design), 7.5.1.

7.5.2 Allowable displacement and deformation It shall be in accordance with JSCE Standard Specification (Design), 7.5.2.

7.5.3 Verification of displacement and deformation It shall be in accordance with JSCE Standard Specification (Design), 7.5.3.

[COMMENT]: Verification of displacement and deformation is normally to be done according to JSCE Standard Specification (Design), 7.5.3, although where the Young’s modulus of the CFRM is extremely low compared to the steel reinforcement, and where the quantity of reinforcement is low, the deformation will be greater than in conventional steel reinforced concrete members. The increased deformation makes shear cracking more likely, and this in turn is considered to affect the displacement and deformation of the whole structure. In cases where shear cracking occurs, it must be properly allowed for in calculating deformation levels.

7.6 VIBRATION It shall be in accordance with JSCE Standard Specification (Design), 7.6.

- 31 -

CHAPTER 8: FATIGUE

8.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 8.1.

[COMMENT]: As with steel reinforcement, CFRM requires verification of fatigue sustained due to repeated tensile stress. Unlike steel, however, CFRM shows significant loss of strength due to secondary stress, and this point must be properly allowed for in examining the fatigue limit state. Tensile or shear reinforcement at intersections with shear cracks i s more liable to undergo fatigue failure. Loss of fatigue strength in tensile reinforcement is not normally considered in conventional steel reinforced concrete members, but it must be allowed for in CFRM.

8.2 VERIFICATION OF FATIGUE It shall be in accordance with JSCE Standard Specification (Design), 8.2.

[COMMENT]: As with steel reinforcement, verification relating to fatigue in CFRM is done by comparing design fatigue strength and design variable stress.

8.3 DESIGN VARIABLE SECTION FORCE AND EQUIVALENT NUMBER OF CYCLES It shall be in accordance with JSCE Standard Specification (Design), 8.3.

[COMMENT]: Miner's hypothesis is thought to be applicable to CFRM as to steel, therefore the number of cycles equivalent to the design variable section force may be calculated in the same manner as for steel. In this case, though, the S-N curve for the fatigue strength of the CFRM is needed.

8.4 CALCULATION OF STRESS DUE TO VARIABLE LOAD (1) Tensile stress in CFRM used for tensile reinforcement may be calculated according to section 7.2. (2) Stress in CFRM used for shear reinforcement may be calculated following JSCE Standard Specification (Design), 8.4(3) for steel shear reinforcement. The shear capacity V cd of concrete without shear reinforcement shall be calculated according to Eq. (6.3.2) of the present recommendation. (3) Stress of steel and concrete shall be calculated according to JSCE Standard Specification (Design), 8.4.

[COMMENTS]: (1), (2) Stress in CFRM may be calculated in the same way as for steel reinforcement, - 32 -

although the shear capacity V cd of concrete without shear reinforcement, which is required for the calculation of stress in shear reinforcement, must be calculated according to Eq. (6.3.2) of the present recommendation, as the calculations differ from those for steel.

8.5 DESIGN SHEAR FATIGUE CAPACITY OF MEMBERS WITHOUT SHEAR REINFORCEMENT Design shear fatigue capacity of flexurally reinforced members without shear reinforcement may be calculated following the provisions for steel reinforced concrete members given in JSCE Standard Specification (Design), 8.5, where V cd and V pcd shall be calculated according to Eqs. (6.3.2) and (6.3.8) of the present recommendation respectively.

[COMMENT]: Design shear fatigue capacity of members without shear reinforcement may be calculated as for steel reinforced members, although the static shear capacity for these calculations when applied to CFRM must be obtained from the equations given in the present recommendations.

- 33 -

CHAPTER 9: SEISMIC DESIGN

9.1 GENERAL It shall be in accordance with JSCE Standard Specification (Seismic Design).

[COMMENT]: The provisions given in JSCE Standard Specification (S eismic Design) may be applied, although as CFRM generally do not yield, when they are used for flexural reinforcement the deformation after flexural yielding exhibited by steel reinforced concrete cannot be relied on.

- 34 -

CHAPTER 10: GENERAL STRUCTURAL DETAILS

10.1 GENERAL It shall be in accordance with JSCE Standard Specification (Design), 9.1, where "steel" shall be taken to signify "steel or CFRM".

10.2 CONCRETE COVER (1) Concrete cover shall be determined taking i nto consideration the quality of concrete, bar diameters, environmental conditions, errors in construction, and the importance of the structure. (2) The minimum concrete cover shall be obtained from Eq. (10.2.1), and shall be not less than the bar diameter.

cmin

= α ⋅ c0

(10.2.1)

where cmin = minimum cover

α = cover factor dependent on design strength of concrete f' ck , as follows: f' ck ≤ 18 N/mm2: α = 1.2 18 N/mm2 < f' ck ≤ 34 N/mm2: α = 1.0 34 N/mm2 < f' ck : α = 0.8 c0 = basic concrete cover, dependent on member as shown in Table 10.2.1 Table 10.2.1: Values of

Member c0

c 0 (basic

Slab 25

concrete cover; mm)

Beam 30

Column 35

(3) Concrete placed directly in the earth for footings or important members of structures, concrete cover should be not less than 75 mm. (4) Concrete cover for concrete placed under water should be not less than 75 mm. (5) Where concrete is vulnerable to abrasion by running water or similar, concrete cover should be increased as appropriate. (6) Members placed in an acid river or subjected to severe chemical action shall be appropriately protected. (7) Concrete cover in structures requiring special fire protection shall be determined taking into consideration the heat resistance of the CFRM, fire temperature and duration, aggregate characteristics etc.

- 35 -

[COMMENTS]: (1) Adequate concrete cover of CFRM is necessary to realize full bond strength with the CFRM, to prevent deterioration of the CFRM, and to protect the CFRM in fires. Concrete cover should therefore be determined based on the designer's experience, taking into account the quality of the concrete, the characteristics and diameter of the CFRM, the effects of harmful substances acting on the concrete surface, the dimensions of the member, construction errors, the importance of the structure and so forth. (2) Eq. (10.2.1) gives the minimum concrete cover. CFRM is generally highly resistant to corrosion, therefore there is no need to make special allowance for environmental conditions in table 10.2.1. Where CFRM is arranged in bundles, the diameter of the reinforcement shall be deemed to be that of a single rod of cross-sectional area equivalent to the sum of the cross-sectional areas of the individual strands in the bundle. (3) This value may be reduced by a further 25 mm, provided the quality of cover is adequately assured by, for example, the use of high fluidity concrete. (4) Concrete placed under water cannot be adequately compacted, the concrete sometimes does not adequately fill narrow spaces between the CFRM and the formwork, and the quality of underwater concrete is hard to determine, therefore a safe minimum of 75 mm has been set. For cast-in-place concrete piles etc., cover should be around 125 mm to allow for the presence of casings, irregularity of the inner face of drilled earth, installation of cages etc. All of these values are reduced by 25 mm from those given for steel reinforcement, in consideration of the superior corrosion resistance of CFRM which allows underwater environments to be treated as standard environments. (5) Where concrete is vulnerable to abrasion, for instance on the upper side of a slab without effective protection, concrete cover should be increased by at least 10 mm, giving a section larger than the minimum required according to bearing capacity calculations. (6) Members placed in acid rivers or exposed to strong chemical action should be provided with extra corrosion protection, as deterioration of the concrete cover cannot be prevented. (7) A "structure requiring special fire protection" refers here to a s tructure showing little or no damage or weakness during a fire. Tests have found that the fire resistance of CFRM varies greatly from type to type, and the fire resistance of the proposed CFRM must be allowed for in determining concrete cover. If necessary the sue of additional fire-proofing layers etc. should be considered.

10.3 CLEAR DISTANCE It shall be in accordance with JSCE Standard Specification (Design), 9.3, where "steel" shall be taken to signify "steel or CFRM".

- 36 -

10.4 BENT CONFIGURATIONS OF REINFORCEMENT 10.4.1 General (1) CFRM may be placed bent within their elastic limit. The effects of elastic bending stress shall be allowed for in design. (2) When bent CFRM is used, the design strength of the bent section shall be allowed for.

[COMMENT]: (2) The design strength of bent sections of CFRM is obtained from 3.4.1(3) or (4).

10.4.2 Stirrups, ties and hoops (1) CFRM may be bent in closed, spiral, grid or solid configurations for use as stirrups, ties or hoops. (2) The standard inside radius of bent sections of stirrups and hoops shall be 2 ø, where ø = bar diameter.

[COMMENTS]: (1) Ties and hoops serve to prevent buckling of axial reinforcement while constraining the inner concrete. They must therefore be closely spaced to ensure adequate effectiveness, and the ties and hoops themselves must be properly anchored. For this reason, the use of closed configurations is advised. Whichever configuration is used, the strength of bent sections and the panel points must be allowed for. (2) The inside radius of bent sections of stirrups and hoops should be small as possible, from the practical point of view of containing the reinforcement, but making the inside i nside radius too small could result in significant loss of strength.

10.4.3 Other reinforcement (1) The inside radius of bends in reinforcement along the outer side of a corner in a frame structure shall be not less than 10 times the reinforcement diameter. (2) Reinforcement along the inner sides of corners in a haunch or rigid frame shall not be bent reinforcement carrying tension of slabs or beams.

Fig. 10.4.1: Inside radius of bend in reinforcement along outer side of corner in frame structure - 37 -

Fig. 10.4.2: Reinforcement along inner side of corner in haunch or frame structure

10.5 ANCHORAGES 10.5.1 General (1) Reinforcement ends shall be embedded sufficiently in concrete, and anchoring shall be achieved either by the bonding force between the reinforcement and concrete, or by mechanical anchoring. (2) At least 1/3 of the positive moment reinforcement in slabs or beams shall be anchored beyond the support, without being bent. (3) At least 1/3 of the negative moment reinforcement in slabs or beams shall extend beyond the inflection point and anchored in the compression zone, or shall be connected to the next negative moment reinforcement. (4) Stirrups shall enclose positive or negative moment reinforcement, and their ends shall be either closed or anchored in the concrete on the compression side. (5) Spiral reinforcement shall be anchored in concrete encl osed by spiral reinforcement wound an extra one and a half turns. (6) When the end of reinforcement is anchored by bonding between concrete and reinforcement, anchoring shall be done following the development length given in 10.5.2.

[COMMENTS]: In CFRM reinforced concrete, the CFRM and concrete must act in concord against external forces. Thus, when there is an external force acting against concrete members, the anchoring of the reinforcement is extremely important, and must be developed free from defects. If the anchoring of the reinforcement ends is adequate, the effects of local bond may be ignored, thus in this section only development of bar ends is covered. (1) CFRM may be categorized as follows according to their bond property. [1] Bond failure by bond splitting of concrete: This is equivalent to the failure mode of deformed steel bars, and in general, this is the mode of failure observed when the surface of the CFRM is treated to resemble a deformed steel bar. - 38 -

[2] Bond failure by pull-out of reinforcement: This mode of failure is generally observed where indentations on the surface of the CFRM are small, or where abrasive grains or threads are bonded onto the CFRM surface, but the bond strength is low. [3] No bond strength: CFRM with smooth surfaces generally has lower bonding action with concrete than conventional round steel bars, giving almost no bond strength at all. In these cases mechanical anchoring is required. [4] Anchoring by resistance from intersecting lateral reinforcement: In lattice and solid configurations, anchoring is generally achieved by the resistance of intersecting lateral reinforcement. In order to achieve full strength of reinforcement, depending on the bond characteristics of the CFRM used, either an adequate development length should be allowed or a mechanical anchorage fitted to embed the reinforcement securely within the concrete, in order to ensure the CFRM does not pull out from the concrete. Given that CFRM looses strength in bent sections, and that their flexural rigidity is inadequate, unlike the case with steel reinforcement no anchoring effect is expected from hooks. Where bond between the reinforcement and the concrete is relied on for anchoring, reinforcement must also be arranged perpendicularly, to ensure adequate anchoring. For tensile reinforcement at the fixed ends of members, both ends of tensile reinforcement in footings, tensile reinforcement at the free ends of cantilever beams and so forth, anchorages should be fitted to prevent reinforcement pulling out even if major cracking appears. (4) When a diagonal crack occurs in a beam, the two parts of the beam on either side of the crack will tend to part from one another. Stirrups are place to prevent these two parts from separating, performing the function of a vertical tensile member of a Howe truss. The stirrup s tirrup must therefore either be closed, or bent so that its end is hooked around reinforcement in the compression zone, to ensure that its end is properly anchored. The purpose of enclosing compression reinforcement with sti rrups is to anchor the stirrup properly, and to prevent the compression reinforcement from buckling.

10.5.2 Development length of reinforcement (1) The development length for CFRM l 0 shall be not less than the basic development length l d d. Where the quantity of reinforcement placed A f is greater than the quantity required by calculation A fc, development length l length l 0 may be reduced in accordance with Eq. (10.5.1)

l0

≥ ld ⋅ ( A fc

/ A f )

(10.5.1)

where l 0 ≥ l d l 0 ≥ 10ø d/3, ø = diameter of reinforcement (2) The development length of reinforcement where the anchorage is bent shall be as follows: (i) When the inside radius of the bend is not less than 10 times the reinforcement diameter, the entire length of reinforcement including the bent part shall be effective. (ii) When the inside radius of the bend is less than 10 times the reinforcement diameter and the straight part beyond the bend is extended more than 10 times the reinforcement diameter, only the straight part beyond the bend shall be effective. - 39 -

(iii) The length of the straight part l' shall shall be not less than the length necessary for the stress acting on the reinforcement in the bent part not to exceed the tensile strength of the bent part.

Fig. 10.5.1: Determination of development length of reinforcement in bent anchorages

(3) Tensile reinforcement shall generally be anchored in concrete not subject to tensile stress. If either of the conditions (i) or (ii) below is sati sfied, tensile reinforcement may be anchored in concrete subject to tensile stress. In this case, the anchorage of the tensile reinforcement shall be extended by (l ( l d + d + l l s) from the section where the reinforcement is no longer required to resist calculated flexure, where l d the d is basic development length and l s may in general be the effective depth of the member section. (i) The design shear strength shall be not less than 1.5 times the design shear force between the point of reinforcement cutoff and the section where the reinforcement is no longer required to resist calculated flexure. (ii) The design flexural capacity shall be not less than 2 times the design moment at a point where adjacent reinforcement terminates, and design shear capacity shall be not less that 4/3 times the design shear force between the point of reinforcement cutoff and the section where the reinforcement is no longer required to resist calculated flexure. (4) Where positive moment reinforcement in a slab or beam is anchored beyond the support at the end, the development length of the reinforcement shall be not less than l 0 for stress in reinforcement at a section which is at a distance of l s from the center of the support and shall be extended to the end of the member.

[COMMENTS]: (1) The development length is calculated from the basic development length l d d , determined by the type and arrangement of the reinforcement, and by the strength of the concrete, modified according to the usage conditions. Where the quantity of reinforcement placed is in excess of that quantity required according to calculation, the basic development length may be reduced proportionally. A minimum value for l 0 has been given, as the safety level with regard to additional forces is reduced. (2) (iii) As the tensile strength of bent s ections of CFRM is generally less than that of straight sections, it is necessary to reduce the tensile force acting on the bent section by the bonding at the straight length l' . Where the quantity of reinforcement placed is in excess of that quantity required according to calculation, length l' may may be reduced following section (1) above. - 40 -

10.5.3 Basic development length (1) The basic development length of CFRM shall generally be determined on the basis of appropriate testing. (2) The basic development length of tensile reinforcement types which undergo bond splitting failure may be calculated according following Eq. (10.5.2), provided that ld > 20ø.

l d

= α1

f d 4 f bod

φ

(10.5.2)

where ø = diameter of main reinforcement f d d = design tensile strength of CFRM f bod bod = design bond strength of concrete according to Eq. (10.5.3), where

f bod

= 0.28α 2 f ' ck 2/ 3 /γ c

(N/mm2)

γc = 1.3

(10.5.3)

where 2 f bod bod ≤ 3.2 N/mm

equal to or results.

α2 = modification factor for bond strength of CFRM; α2 = 1.0 where bond strength is greater than that of deformed steel bars; otherwise α2 shall be reduced according to test f' ck ck = characteristic compressive strength of concrete

α1 = 1.0 (where k c ≤ 1.0) = 0.9 (where 1.0 < k c ≤ 1.5) = 0.8 (where 1.5 < k c ≤ 2.0) = 0.7 (where 2.0 < k c ≤ 2.5) = 0.6 (where 2.5 < k c ) where

k c

=

c

φ

+

15 At E t sφ

⋅

E 0

(10.5.4)

c = downward cover of main reinforcement or half of the space between the anchored reinforcement, whichever is the smaller At = area of transverse reinforcement which is vertically arranged to the assumed splitting failure surface s = s = distance between the centers of the transverse reinforcement E t t = Young’s modulus of transverse reinforcement E 0 = standard Young’s modulus (= 200 kN/mm 2) (3) Where the reinforcement to be anchored is located at a height of more than 30 cm from the final concrete surface during concrete placement and at an angle of less than 45° from the horizontal, the basic development length shall be 1.3 times the value of l d d obtained from the application of section (2). (4) The basic development length of compression reinforcement shall be 0.8 times the values of l d d obtained from the application of sections (1), (2) and (3).

- 41 -

[COMMENTS]: (1) The development length of CFRM varies with the reinforcement type, concrete strength, concrete cover and transverse reinforcement. These factors must be adequately allowed for in testing. For this reason, the test method(s) used to determine the development length of a CFRM should be methods which reflect the actual bond characteristics within the member, such as methods using test beams or lap jointed test specimens. JSCE-E 539 "Test Method for Bond Strength of Continuous Fiber Reinforcing Materials by Pull-Out Testing" does not reflect the actual bond characteristics within the member, and thus will generally over-estimate bond strength. Calculation of basic development length substituting bond strengths obtained from this test for f for f bod bod should thus be avoided. (2) In the JSCE Standard Specification (Design), the required development length for steel reinforcement with transverse reinforcement is given as Eq. (C 10.5.1)

l 0

 f yd   − 13.3 φ  1.25 f ' cd  =  c 15 At  0.31 318 + 0.79 795 +   φ sφ 

(C 10.5.1)

where f yd = design tensile yield strength of steel reinforcement (N/mm 2) 2 f' cd cd = design compressive strength of concrete (N/mm )

c/φ

≤

2.5

This equation is further simplified by factoring in a factor

α, given in the present recommendation.

Fig. C 10.5.2 Comparison of bond strength Eq. (C 10.5.2) with test results - 42 -

For CFRM with deformed surfaces which fail by bond splitting, comparison of the bond strength obtained from testing of this bond splitting and the bond strength calculated according to the formula below, derived allowing for the ratio of the Young’s modulus of the CFRM used as transverse reinforcement E t (= E f ) to the standard Young’s modulus E 0 (= E s) yields the following formula:

 c 15 At E t  + ⋅   φ sφ E 0 

0.318 + 0.795 f bod

=

3.2 f ' c

−

53.2

(C 10.5.2)

f y

Based on Eq. ( C 10.5.2), evaluation of the basic development length according to the method used for deformed steel bar has been allowed for any CFRM that fails by bond splitting. For CFRM that fail by bond splitting but show bond strength that is not equal to or greater than that of deformed steel bars, if the design bond strength is estimated following Eq. (10.5.3), a modification factor α2 (≤1.0) shall be factored in. Where the data available is inadequate or where significant variation is found, the basic development length shall generally be determined by appropriate testing. The basic development length of reinforcement where the bond failure mode is by pull-out may be determined by appropriate testing.

10.6 SPLICES 10.6.1 General It shall be in accordance with JSCE Standard Specification (Design), 9.6.1, where "steel" shall be taken to signify "steel or CFRM".

10.6.2 Lap splices Lap splices for longitudinal reinforcement shall follow the JSCE Standard Specificat ion (Design), 9.6.2, where "steel" shall be taken to signify "steel or CFRM".

[COMMENT]: Where the quantity of reinforcement place A f is greater than the calculated requirement A fc, the length of lap splices may be reduced by factoring in A fc/ A f , determined as specified in the present recommendation (above). Where A fc/ A f > 350/ f d , A fc/ A f = 350/ f d , where f d = design tensile strength of CFRM (N/mm2).

- 43 -

CHAPTER 11: PRESTRESSED CONCRETE

11.1 GENERAL (1) This chapter gives general guidelines required for the design of prestressed concrete structures or members with CFRM tendons or CFRM tendons in conjunction with steel tendons. (2) Prestress levels shall be determined to ensure that the structure or member can fulfill its purpose safely and economically and give the desired performance.

[COMMENTS]: Prestressed concrete structures make possible improvement of the crack characteristics at the serviceability limit state as well as reduction of the cross sectional area of a member, thus offering an extended range of options for many types of structure. Design calculations of prestress force in concrete members are generally handled by regarding prestress forces in the serviceability limit state as loads, considering only the statically indeterminate forces in loads when the effects of prestress forces are included in calculation of cross-sectional bearing capacity at ultimate limit state. In this case, the ultimate strain of CFRM has to be checked. Where member forces are calculated other than by linear analysis, prestress forces must be handled in the appropriate manner for the analysis method used. (1) The provisions of this chapter shall be applied to general prestressed concrete structures or members with CFRM tendons or CFRM tendons in conjunction with steel tendons. These provisions shall not be applied to the following types of structures or members: [1] Structures or members where the prestress force is transferred by a method other than prestressing tendons; for example methods to use a jack to give prestress to arch members or concrete pavement, methods using expanding agent to introduce prestressing, or methods whereby concrete is cast on the tension side of a steel girder to which flexural moment has previously been applied, subsequently releasing the moment to induce prestressing after the concrete has hardened. [2] Prestressed steel reinforced concrete structures or members; prestressed composite structures or members consisting of steel and concrete. [3] Prestressed concrete members or structures constantly exposed to abnormal temperatures, where "normal temperature" is taken to signify a temperature within the range 0°C~40°C. [4] Factory products such as prestressed concrete piles, prestressed concrete pipes, etc. For structures or members having unbonded prestressing tendons ("unbonded CFRM") and structures or members wherein which CFRM is used as external cables, considerations other than those given here must be allowed for; these will include the increase in flexural cracking widths due to the lack of bond with the concrete members, the reduction of flexural capacity, the minimum reinforcement quantity, fatigue resistance of the anchoring devices etc. In s tructures with external cables which are exposed to a fire risk, fireproofing measures will be required.

- 44 -

(2) Prestressing may generally be determined for limit states at the tensile edge, according to the function of the structure (cf. 11.2)

11.2 CATEGORIZATION OF PRESTRESSED CONCRETE It shall be in accordance with JSCE Standard Specification (Design), 10.2.

11.3 PRESTRESS FORCE (1) Prestress force shall be calculated according to Eq. (11.3.1).

P ( x )

=

Pi

− [ ∆Pi ( x ) + ∆Pt ( x )] + ∆PT ( x )

(11.3.1)

where P ( x) = prestress force in design section under consideration P i = prestress force during prestressing due to tension applied to tendon ends

∆ P i( x) = loss of prestressing force during and immediately after prestressing, to be calculated allowing for the following effects: [1] elastic deformation of concrete [2] friction between tendon and duct [3] set loss on anchoring of tendon [4] other considerations

∆ P t ( x) = time-dependent loss of prestressing force, to be calculated allowing for the following effects: [5] relaxation of tendon [6] creep of concrete [7] shrinkage of concrete

∆ P T ( x) = variation of prestress force due to temperature change (2) In calculating the indeterminate forces at the serviceability limit state or the fatigue limit state, the prestress force given by Eq. (11.2.1) may be considered to be the characteristic value for the prestress forces.

[COMMENTS]: (1) The effects to be considered in calculating prestress losses ∆ P i( x) and ∆ P t ( x) in relation to calculation of prestress force. [1] Effects of elastic deformation of concrete: Prestress loss due to elastic deformation of concrete shall always be considered when the pretensioning system is used (c.f. Eq. (C 11.3.1)). When post-tensioning tendons are tensioned consecutively, the prestress loss due to elastic deformation of concrete shall be calculated. In such cases, the average prestress loss may be calculated in accordance with Eq. (C 11.3.2). (pretensioning)

∆σ p = nσ ' c pg

(C 11.3.1)

- 45 -

(post-tensioning)

∆σ p =

1 2

nσ ' cpg

N − 1 N

(C 11.3.2)

where

∆σ p = prestress loss in tendon n = Young’s modulus ratio E p/ E c

σ' cpg = compressive stress of concrete at tendon centroid due to tensioning N = number of tendon tensionings (i.e. number of tendon groups) E c = Young’s modulus of concrete E p = Young’s modulus of tendons; for CFRM E p = E f [2] Effects of friction between tendon and duct: prestress loss in prestressing tendons due to friction depends on the condition of the inner surface of the duct, the type of prestressing tendon, and the positioning of tendons. Loss of prestressing tendon force due to friction can generally be divided into two terms, one related to the angular change of the centroid line of the prestressing tendons, and the other related to the length of the prestressing tendons. The tensile force in the prestressing tendon at the design section may be expressed by Eq. (C 11.3.3).

P x

=

Pi e − ( µα + λ x )

(C 11.3.3)

where P x = tensile force of tendon at design section P i = tensile force at position of prestressing jack

µ = coefficient of friction per radian of angular change α = angular change (radians) (c.f. Fig. C 11.3.1) λ = coefficient of friction per unit length of tendon x = distance from tensioned edge of tendon to design section

Fig. C 11.3.1: Angular change of tendon centroid line

The values of µ and λ will vary depending on the tendon and sheath material, and must therefore be determined by testing, but where sheaths are used with CFRM, the tensile force in the tendon may generally be calculated with µ = 0.3, λ = 0.004. [3] Effects of set loss on anchoring of tendon: Where there is set loss during anchoring of tendons, the resultant prestress loss must be allowed for. Set loss is especially significant with wedge-type anchorage systems, therefore the prestress loss and the length affected by it must be examined prior to tensioning by applying the assumed set loss based on available data. "Set loss" refers to the pulling of a tendon into - 46 -

the anchoring device during anchoring. The amount of set loss varies depending on the type of anchoring device, and must therefore be studied separately for each type. Where there is no friction between the prestressing t endons and the duct, loss of prestressing force due to set loss is calculated according to Eq. (C 11.3.4).

∆ P =

∆l l

× A p E p

(C 11.3.4)

where

∆ P = loss of prestressing force due to set loss ∆l = set loss l = length of tendon A p = cross-sectional area of tendon Where there is friction between the prestressing tendons and the duct, loss of prestressing force in the tendons may be calculated as follows. Assuming identical frictional force during tensioning and releasing, the distribution of tendon force is as shown in Fig. C 11.3.2. When a tendon is tensioned from end a, the prestressing force in the tendon is a'b'co' i mmediately prior to anchoring, and the prestressing force at the tensioning end immediately after to anchoring decreases to P t . In this case, lines a'b'c and a''b''c are symmetrical with respect to the horizontal axis ce, and the amount of set is equal to the area Aep enclosed by a'b'cb''a'', divided by A p E p.

∆l =

Aep

(C 11.3.5)

A p E p

Thus, the line cb''a'' may be obtained by determining the point c where Aep is equal to ∆lA p E p.

Fig. C 11.3.2: Distribution of tendon force

[4] Other effects: these will include e.g. deformation of joints used in precast block construction [5] Effects of relaxation of tendon: loss of prestressing force in tendons due to tendon relaxation may be obtained from Eq. (C 11.3.6).

∆σ pr = γσ pt

(C 11.3.6) - 47 -

where

∆σ pr = loss of prestressing force in tendons due to tendon relaxation γ =

apparent relaxation rate in tendon

[6] Creep of concrete, [7] Shrinkage of concrete: loss of prestressing force in tendons due to creep and shrinkage of concrete are determined on the basis of appropriate creep analysis; in general COMMENTS (1) (ii) to section 11.4 below may be applied.

Owing to the difference between the thermal expansion coefficients and the Young’s modulus of concrete and CFRM, the prestressing of CFRM varies with temperature; for example a prestress loss of around 2% is found for a temperature rise of 20°C in the case of carbon fiber CFRM. This effect must therefore be allowed for where major temperature variations are expected. Prestress loss due to temperature change may be obtained from Eq. (C 11.3.7).

∆σ pT = ∆T (α f − α CON ) E f

(C 11.3.7)

where

∆σ pt = prestressing force loss in CFRM due to temperature change ∆T = temperature change α CON =

thermal expansion coefficient of concrete

α f =

thermal expansion coefficient of CFRM E f = Young’s modulus of CFRM (2) For indeterminate structures, it is possible to prevent indeterminate forces due to prestressing by selecting the appropriate tendon arrangement. Generally, though, indeterminate forces occur when member deflection due to prestress force is restricted, and these indeterminate forces must be allowed for when calculating stresses acting on the cross sections. It should be noted that the level of indeterminate forces due to prestress forces are significantly affected by changes in the cross-sectional area of the member.

11.4 SERVICEABILITY LIMIT STATE 11.4.1 Flexural moments and axial forces (1) Stress calculation (i) Stress calculation Stress in concrete, CFRM and steel shall be calculated according to 7.2, based on the following assumptions etc.: [1] In prestressed concrete structures, the entire concrete section is effective [2] In prestressed reinforced concrete structures, the tensile stress of concrete shall generally be ignored [3] Strain increase in bonding tendons is identical to that at the same position in concrete [4] Axial ducts in members are not considered part of the effective cross-section [5] The section constant of the integrated tendons and concrete shall be determined allowing for the - 48 -

Young’s modulus ratio of the tendons and the concrete. (ii) Stresses in concrete, CFRM and steel subjected to permanent load shall be determined allowing for the effects of tendon relaxation, creep and shrinkage of concrete, and the constraining effect of steel. (iii) Stresses in concrete, CFRM and steel subjected to variable loads shall be determined based on the stress under permanent loads calculated in (ii) above. (2) Limiting values of stress Limiting values for compressive stress in concrete due to flexural moment and axial forces shall be according to section 7.3 above. Limiting values for tensile stress in tendons shall be determined based on testing, according to the type of tendon sued. Limiting values for prestressi ng steel shall be according to JSCE Standard Specification(Design), 10.4. (3) Examination for prestressed concrete structures (i) Limiting values for edge tensile stress in concrete shall be the design tensile st rength, allowing for the effects of member dimensions. (ii) Where edge tensile stress of concrete acts as tensile stress, in general a quantity of tensile steel in excess of the cross-sectional area calculated according to Eq. (11.4.1) shall be arranged. Deformed bars shall generally be used for steel reinforcement.

A s

= T c / σ st

(11.4.1)

where A s = cross-sectional area of tensile steel T c = total tensile force acting on concrete limiting value for tensile stress of tensile steel, may be set at 200 N/mm 2 for deformed bars. Bonding prestressing steel arranged in concrete where tensile stresses occur may be regarded as σ st =

tensile steel. In this case, the limiting value for tensile stress of prestressing steel used in pretensioning may be set at 200 N/mm 2, and at 100 N/mm 2 for prestressing steel used in post-tensioning. (4) Examination for prestressed reinforced concrete structures Verification of flexural cracking shall be according to section 7.4 above. (5) Verification of deflection shall be according to section 7.5 above, allowing for the effects of prestressing.

[COMMENTS]: (1)(i): [3] In calculating strain increase in external cable tendons and unbonded tendons (i.e. unbonded CFRM or unbonded prestressing steel), the assumption of “plane remains plane” cannot be applied, therefore separate study is required. In this case, concrete stress may be calculated ignoring stress increase in tendons, regarding the structure as a reinforced concrete structure subject to eccentric axial force due to the effective prestress force.

- 49 -

[4] Grouting in ducts is not subject to prestress, therefore ducts in the axial direction of the member should not be included in the effective section, even when grouted. (1) (ii) Where there is bond between the concrete and the tendons, stresses in the concrete, tendons and steel under permanent load shall be calculated as follows. [1] Prestressed concrete structures: The constraining effect of steel may be ignored in prestressed concrete structures. The reduction in tensile stress of tendons may in this case be calculated according to Eq. (C 11.4.1):

∆σ pcs =

n p ⋅ ϕ (σ ' cpt +σ ' cdp ) + E p ⋅ ε ' cs 1 + n p ⋅

σ ' cpt σ pt

ϕ  ⋅   1 +  2

(C 11.4.1)

where

∆σ pcs = tensile stress reduction in tendons due to concrete creep and shrinkage ϕ

= creep factor

ε ' cs =

shrinkage strain of concrete n p = ratio of Young’s modulus of tendons to that of concrete σ pt =

tensile stress of tendons immediately after tensioning

σ ' cpt

= compressive stress of concrete at tendons due to prestressing immediately after

tensioning σ ' cdp =

compressive stress of concrete at tendons due to permanent load

[2] Prestressed reinforced concrete structures In prestressed reinforced concrete structures, the constraining effect of steel is generally considered in calculations. In this case, the reduction of tensile stress in tendons and the stress change in tensile reinforcement may be calculated according to Eqq. (C 11.4.2) and (C 11.4.3). Stress in concrete where cracking does not occur under permanent loads shall be calculated allowing for the effects of the reaction force of the compressive forces acting on tensile reinforcement.

{1 + α pp ⋅ (1 + ϕ / 2 )} ⋅ ∆σ pcs

+ α sp ⋅ (1 + ϕ / 2 ) ⋅ ∆σ scs

= n p ⋅ {ϕ ⋅ (σ ' cpt +σ ' cdp ) + E c ⋅ ε ' cs } α ps

(C 11.4.2)

⋅ ∆σ scs ⋅ (1 + ϕ / 2) ⋅ ∆σ pcs + {1 + α ss ⋅ (1 + ϕ / 2 )}

= n s ⋅ {ϕ ⋅ (σ ' cps +σ ' cds ) + E c ⋅ ε ' cs }

(C 11.4.3)

given that α pp

= n p ⋅ A p ⋅ (1 / Ac + e p 2

α ps

= n s ⋅ A p ⋅ (1 / Ac + e p ⋅ e s / I c )

α sp

= n p ⋅ As ⋅ (1 / Ac + e p ⋅ e s / I c )

/ I c )

- 50 -

α ss

= n s ⋅ As ⋅ (1 / Ac + e s 2

/ I c )

where

∆σ pcs = tensile stress reduction in tendons due to concrete creep and shrinkage ∆σ scs = variation in tensile reinforcement stress due to concrete creep and shrinkage ϕ =

creep factor

ε'cs = shrinkage strain of concrete n p, n s = ratio of Young’s modulus of tendons and steel to that of concrete n p = E p/ E c; for CFRM n p = E f / E c, n s = E s/ E c σ ' cpt

= compressive stress of concrete at tendons due to prestressing immediately after

tensioning σ ' cps =

compressive stress of concrete at steel reinforcement due to prestressing immediately

after tensioning σ ' cdp =

compressive stress of concrete at tendons due to permanent load

σ ' cds =

compressive stress of concrete at steel reinforcement due to permanent load A p = cross-sectional area of tendons A s = cross-sectional area of steel reinforcement e p = distance from centroid axis of member section to centroid of tendon e s = distance from centroid axis of member section to centroid of steel reinforcement Ac = total cross-sectional area of concrete I c = moment of inertia of total concrete section The effective prestress of unbonded tendons and tendons used in external cabling can in theory be calculated by first determining the stress changes along the entire tendon length at the centroid of the tendon due to deformation of concrete members, then calculating stress changes in the tendon from the average strain. As this calculation would be enormously complex, while member deformation at the serviceability limit state is minimal and the effects of strain changes at the tendon positions are slight, Eq. (C 11.4.1) may also be applied to external cabling. (2) If concrete cracking, prestressing steel fatigue etc. are studied, there is no particular need to limit tensile stress in concrete and prestressing steel, but once tensile stresses exceed the elastic limit, the assumptions made in structural analysis and stress calculation fail to hold good, and prestress force can no longer be treated as an external force. For this reason, tensile stress must be kept below the elastic limit stress. Consistency has also been allowed for in long-term relaxation testing of prestressing steel, where the initial load was set at 70% of the characteristic value of the tensile strength of prestressing steel. Unlike reinforcing or prestressing steel, CFRM is liable to fail below their static strength (creep failure) when subjected for long periods to significant, sustained stress for long periods. When using CFRM tendons, therefore, the tension must be set allowing for the creep failure strength. Creep failure s trength is calculated on the basis of JSCE-E 533 "Testing Method for Creep Failure of Continuous Fiber Reinforcing Materials", testing up to 1000 hours and extrapolating creep failure strength at 1 million hours. The limit value for tensile stress of tendons may generally be taken as the creep failure strength characteristic value f fck , multiplied by a reduction factor of 0.8. The limit value shall be not more than 70% of tensile strength (c.f. 7.3).

- 51 -

(3) (i) Limiting values for edge tensile stress in concrete for prestressed concrete structures is taken as being the design tensile strength, allowing for the effects of member dimensions according to Eq. (C 7.4.1) in the JSCE Standard Specification (Design). Table C 11.4.1 gives limiting values for edge tensile stress. Table C 11.4.1: Limiting values for edge tensile stress in concrete for prestressed concrete structures

Loading status

Section depth

(m)

Subject to variable load

0.25 0.5 1.0 2.0 3.0 ~

30 2.1 1.7 1.3 1.1 0.9

Design strength f' ck (N/mm2) 40 50 60 70 2.6 3.0 3.4 3.8 2.1 2.4 2.7 3.0 1.6 1.9 2.2 2.4 1.3 1.5 1.7 1.9 1.1 1.3 1.5 1.7

80 4.1 3.3 2.6 2.0 1.8

(ii) Provision is made for calculation of the tensile steel quantity to be placed where the concrete is subject to tensile stress, minimizing the difference between section stress calculated assu ming the entire concrete section to be effective and section stress calculated assuming cracking to be present. The quantity of tensile steel may be calculated either by the method given here, or by a method ignoring the tensile stress of concrete. For tensile stresses up to the level of the design strength, the method given here has been adopted as it is simpler and also more conservative. If CFRM tendons are considered as being equivalent to tensile reinforcement, the strain limit value may be substituted for the limiting value for stress in prestressing steel, and this strain limit value applied to CFRM. A distinction is drawn between pre- and post-tensioning tendons, to allow for the different bond strengths to the concrete in the two systems. When unbonded tendons are used, the required quantity of tensile steel may be calculated multiplying the value by 1.35 with regard to variable loads. Unbonded tendons are not regarded as tensile reinforcement, as in prestressed concrete with small quantities of steel reinforcement may be liable to significant crack concentrations with attendant steel corrosion. Concrete members used in external cabling systems are to be arranged with the minimum quantity of steel for reinforced concrete members subject to flexure. No additional variable loads are to be factored into the calculation of tensile steel quantities. Tendons placed as external cables are not regarded as tensile reinforcement. (4) For prestressed reinforced concrete structures, a limit value for crack width shall be determined based on environmental conditions, the function and purpose of the structure or member, etc., and flexural cracking studied according to 7.4. In this case, the increase in tensile reinforcement stress may be calculated according to (1)(iii), and flexural crack widths calculated with regard to durability according to Eq. (7.4.1). - 52 -

In prestressed reinforced concrete structures, unbonded tendons, external cabling tendons etc. are used in conjunction with deformed steel bars. Corrosion-proofing for prestressing steel is considered separately, while CFRM is not liable to corrosion. As flexural crack widths are normally studied with regard to the outermost layer of deformed steel bars, the standard method of calculation of flexural crack widths may be adhered to.

11.4.2 Shear and torsion It shall be in accordance with JSCE Standard Specification (Design), 10.4.2.

11.5 ULTIMATE LIMIT STATE Verification of ultimate limit state for sectional failure shall be done in accordance with Chapter 6.

[COMMENTS]: When unbonded tendons are used, flexural capacity is generally lower than when bonding tendons are used. For this reason, flexural capacity shall be reduced by 30% except in s pecial cases where allowance is made for tensile stress of tendons, tendon layout, flexural moment distribution, coefficient of friction between tendons and concrete etc. When ducts etc. are provided perpendicular to the member axis for transverse reinforcement etc., the duct sections need not be deducted from the concrete section. Duct sections shall be deducted from the concrete section in the following cases: [1] When ducts etc. are not grouted [2] When the diameter of the ducts etc. exceeds 30% of the member thickness

11.6 FATIGUE LIMIT STATE It shall be in accordance with JSCE Standard Specification (Design), 10.6, where "steel" shall be taken to signify "steel or CFRM".

11.7 SAFETY DURING CONSTRUCTION The following studies shall generally be made in relation to construction: (1) Tensile stress in tendons during or immediately following prestressing shall be determined by testing, allowing for variations in material strengths. (2) In verifying the safety of flexural moments and axial loads, the tensile s tress of the concrete shall be not greater than the design tensile s trength of the concrete, allowing for scale effect in the members. The design tensile strength of the concrete may be determined using the characteristic value for the compressive strength of the concrete at the time of calculation, taking g c as equal to 1.0. - 53 -

In concrete regions subject to tensile stress, tensile reinforcement having a cross-sectional area of not less than 3/4 of that calculated according to 11.4.1(3) shall be arranged. (3) Flexural compressive stress and axial compressive stress in concrete due to flexural moment and axial forces immediately following prestressing shall be respectively not more than 1/1.7 and 1/2 of the characteristic values for compressive strength of the concrete. (4) Deflection shall be verified in accordance with Section 7.5 above, allowing for the effects of prestressing. (5) The effects of shear and torsion shall be verified in accordance with Section 11.4.2 above. The design tensile strength of the concrete may be determined using the characteristic value for the compressive strength of the concrete, taking

γc as equal to 1.0.

(6) Verification of the ultimate limit state may be done if necessary in accordance with Chapter 6.

[COMMENTS]: The expression "during construction" shall generally be taken to signify the period during prestressing, immediately after prestressing, and subsequent stages until the structure goes into service. (1) The limiting values for tensile stresses during and immediately after prestressing (respectively prestress forces P i and ( P i-∆Pi( x) in Eq. (11.3.1)) are to be determined by testing, given that they vary for different materials, and that tensile strength is subject to significant fluctuations. When carbon fiber CFRM is used, these values will generally be 0.7 f puk and 0.65 f puk respectively. (2) Cracking during construction is generally not permitted, for the following reasons: [1] Difficulty in controlling the width of cracks occurring during construction [2] Difficulty in controlling deformation after loss of rigidity due to cracking [3] Lack of data concerning shrinkage and creep behavior in the compressive zone of cracked concrete at the serviceability limit state When all of the above issues have been adequately resolved, cracking during construction may be permitted. The limit value for flexural tensile stress has been determined based on considerations such as load combinations during construction, magnitude of flexural tensile stress, timing of the onset of flexural tensile stress etc. With regard to short-term tensile stresses, given that the section affected changes to compressive stress in service state, and also that the quantity of tensile steel in the service state is calculated separately, the quantity of tensile reinforcement may be reduced by 1/4, as provided for in this section. This reduction, however, is not recommended for tensile reinforcement subject to long-term tensile stresses, as the crack widths may grow due to creep of concrete.

11.8 STRUCTURAL DETAILS 11.8.1 Prestressing Tendons (1) Clear distance (i) The clear distance between sheaths for post-tensioning tendons shall satisfy the following - 54 -

requirements: [1] Horizontal and vertical spacing between sheaths shall be not less than 4/3 times the maximum size of the coarse aggregate; [2] In areas where an internal vibrator is inserted, the horizontal spacing of sheaths or groups of sheaths shall be not less than 6cm, and the necessary spacing for the internal vibrator shall be maintained; [3] Small size sheaths may be arranged in contact with each other if this is unavoidable. In such cases, the maximum number of sheaths shall be two, in the vertical direction; [4] The vertical spacing between sheaths or groups of sheaths should be not less than the vertical section of the sheath (ii) In pre-tensioning systems, the horizontal and vertical spacing of tendons at member ends shall be not less than 3 times the diameter of the tendon, and the horizontal spacing shall be not less than 4/3 times the maximum size of the coarse aggregate. When tendons are bundled in regions other than member ends, the numbers of layers ad tendons in a group shall be not more than 2 layers and 4 tendons respectively, and the spacing between each group shall be not less than 4/3 times the maximum size of the coarse aggregate. (2) Concrete cover Cover for a tendon, sheath or group of sheaths, and anchoring device shall be not less than the values given in Section 10.2. (3) Arrangement (i) Tendons shall be so arranged that the prestress loss due to friction is low, and that there is no abrupt change in the cross-sectional area of the tendons throughout the member length. (ii) Prestressing tendons shall be extended straight with the required length from the bearing face of the anchoring device. (iii) When straight CFRM is arranged in a curve, the minimum curve radius to which the material may be bent by elastic deformation without causing damage shall first be determined by testing. Measures must be taken to eliminate any discrepancy between design and construction regarding the bending radius, allowing for the effects of secondary stresses on the strength of the reinforcement. The radius shall be determined such that excessive bearing pressure is not exerted on the concrete. (iv) In the vicinity of section where moment reversal occurs due to the combination of loads, tendons should be dispersed between the upper and lower edges of the member section, avoiding concentrations of tendons near the centroid of the section. (v) At an end support of a girder, some of the tendons should be extended along the lower face and anchored near the lower edge of the girder end. (4) Arrangement of anchoring devices and couplers (i) Anchoring devices shall be arranged so that each design section is subjected effectively to the necessary prestress, and that the tendons are securely fastened. Couplers shall be so arranged that the tendons can be securely coupled. (ii) When multiple anchoring devices are arranged in the same section, the section configuration and - 55 -

dimensions of the concrete in the anchorage region shall be determined allowing for the number of anchorage devices, the tendon forces and the required minimum spacing of the devices. (5) Reinforcement for concrete adjacent to anchorage regions Concrete adjacent to anchorage regions shall be reinforced with steel or CFRM, to prevent development of harmful cracks due to tensile stress. (6) Protection of anchorages Anchorages of tendons shall free from damage or corrosion for the duration of the design service life of the structure.

[COMMENTS]: (1) (i) Spacing between sheaths shall generally be determined based on the following considerations. Sheaths should be arranged as described in clauses [1] and [2], and group arrangements should if possible be avoided, in order to ensure that the concrete fully encloses the sheaths and that the entire cross section is filled with concrete. Where group arrangement of sheaths is unavoidable due to limited member thickness and requirements for insertion of internal vibrators etc., vertical arrangements of up t o two sheaths in the vertical direction as described in clause [3] may be used, provided that the sheaths are small and that special considerations are applied. A "small" sheath shall be one with a diameter of not more than approximately 70mm. "Special considerations" refers to sectional properties used i n stress calculations, spacing of sheath bend-up locations, concrete casting method, concrete quality etc. When a sheath is bent, the concrete between sheaths must be capable of withstanding the bearing stress of the tendons acting on the sheath walls. Where sheaths in the direction of the bearing stress at a bend are ungrouted as shown in Fig. C 11.8.1(a) , damage may occur if the clear distance is too small. Generally the clearance should be not less t han one diameter of the sheath, as described in clause [4] (c.f. Fig. C 11.8.1(b)).

Fig. C 11.8.1: Arrangement of curved sheaths

(ii) In pre-tensioning systems, significant bond stress acts between the concrete and the tendons especially at the member ends. The clear spacing required here is given to ensure the development of adequate bond resistance, and adequate compaction of the concrete.

- 56 -

(3) (i) Prestress loss due to friction is proportional to the angle change in the tendons and to tendon length, For bend-up or bend-down of tendons such as those in continuous girders, therefore, the effects of friction loss are considerable. (iv) In continuous girders etc., in zones where loading causes reversal of bending moments, concentration of tendons around the center of the member section will reduce the quantity of reinforcement at the member edges, making cracking more likely. This should be prevented by distributing tendons in the zones close to the upper and lower edges (c.f. Fig. C 11.8.2).

Fig. C 11.8.2: Arrangement of tendons in zones subject to moment reversal due to loading

(v) Where tendons cannot be arranged as described in this clause, the tendons must be replaced by axial reinforcement. (4) (i) In sections around anchorages, propagation of prestress and other effects cause stress disturbance, therefore the section cannot be treated as a normal section subject to eccentric axial loads for the purposes of stress calculation. When the design section is in the vicinity of an anchorage, the calculated prestress is not exerted, therefore the design section and the anchorage must be sufficiently separated to ensure prestressing is exerted effectively. When an anchorage is placed in the central part of a member, it should generally be in the compression zone of the member. The fatigue strength of an anchorage due to repeated loads is generally lower t han the fatigue strength of tendons, therefore when an anchoring device is placed in the center of a member, it should located in a position where stress variation is at a minimum, and sufficiently removed from positions subject to large stress variation. Couplers should be placed either in the vicinity of the centroid of the section, or in positions where bending moment variation is low. For coupling in bent regions, tendons should be kept straight for a certain distance on either side of the coupler, and the coupling must be kept in a straight line. (ii) The required minimum spacing of anchorages and the minimum concrete cover shall be determined by testing. Where the anchoring technique adopted is conventional and known to be sufficiently safe, the conventional practices may be adopted in determining the section configuration and dimensions of the - 57 -

concrete in the anchoring region. (5) Regarding to reinforcing methods for concrete in the vicinity of anchorages in post-tensioning techniques, see JSCE "Recommendations for Design and Construction of Prestressed Concrete (1991 edition), Chapter 3 "Anchorage Design". In pre-tensioning, harmful cracking may occur at the anchorages due to the arrangement and section configuration of tendons, therefore reinforcement must be provided to eliminate adverse effects on member performance. (6) See present recommendation Part 2, "Construction". When anchoring devices are embedded in a member after prestressing, the minimum concrete cover for these devices must be ensured.

11.8.2 Minimum reinforcement (1) The minimum quantity of reinforcement in prestressed concrete shall be 0.1% of the concrete section, where "reinforcement" shall be taken as referring to deformed bars and pre-tensioning tendons. (2) Reinforcing steel, prestressing steel or CFRM placed in accordance with 11.4.1(3) above shall have a minimum diameter of 9mm, and shall be spaced not more than 30cm apart.

[COMMENTS]: (1) Cracking due to shrinkage or temperature gradients may occur in prestressed concrete members prior to prestressing. In order to keep such cracking below harmful levels, all member sections shall include a minimum of 0.1% of the total section area of reinforcing steel, prestressing steel or CFRM. As CFRM has a lower Young’s modulus than steel, placing of an equivalent quantity of CFRM will increase crack widths, but CFRM is also not liable to corrosion, therefore the minimum required quantity of reinforcement has been kept the same both for steel and for CFRM. For prestressed concrete members in post-tensioning, and for prestressed concrete girders in pre-tensioning, the total quantity of steel and the total quantity of CFRM, including bonding tendons, should be not less than 0.15% of the cross-sectional area of the concrete (c.f. 6.2.2). (2) "Prestressing steel or CFRM" refers here to pre-tensioning tendons and grouted post-tensioning tendons.

11.8.3 Joints It shall be in accordance with JSCE Standard Specification (Design), 10.8.4.

- 58 -

CHAPTER 1: GENERAL

1.1 SCOPE (1) This Recommendation (Construction) provides the general requirements relating specifically to the construction of concrete structures using Continuous Fiber Reinforcing Materials, hereafter called CFRM. The requirements given in this Recommendation are based on JSCE Standard Specification for Design and Construction of Concrete Structures (Construction), hereafter called JSCE Standard Specification (Construction). (2) CFRM used in construction shall normally be materials meeting the requirements given in JSCE-E 131 "Quality Standards for Continuous Fiber Reinforcing Materials".

[COMMENT]: CFRM may be used as tendons or as reinforcement in concrete, either singly or in conjunction with prestressing or reinforcing steel. This Recommendation (Construction) gives general requirements relating to the use of CFRM in concrete structures not specified in JSCE Standard Specification (1996). A wide range of CFRM of varying types and quality are available, but for the purposes of this Recommendation, CFRM used shall normally meet the requirement given in JSCE-E 131.

1.2 DEFINITIONS The following terms are defined for general use in this Recommendation (Construction). Reinforcement: Materials used to reinforce concrete. These include steel and continuous fiber reinforcing materials ("CFRM"). Continuous fiber: General term for continuous fibers used for concrete reinforcement. These include carbon fibers, aramid fibers, and glass fibers, etc. Fiber binding materials: Binders are used to solidify continuous fibers together. These are generally plastic materials such as epoxy resin or vinylester resin. Volume ratio of axial fiber: Ratio of the volume of the actual fiber and the volume of fiber arranged in the direction of strengthening of CFRM. Continuous fiber reinforcing materials (CFRM): General term for dimensionally strengthened material for the purpose of reinforcing concrete on being formed by impregnating and hardening continuous fiber with fiber binding material, or only continuous fibers bundled or woven together. CFRM tendons: CFRM used as prestressing materials to induce prestress in concrete mostly used in bar or strand forms. CFRM reinforcement: CFRM other than those used as prestressing materials.

- 59 -

CFRM bar: CFRM in the form of bar similar to reinforcing or prestressing steel. CFRM shape: CFRM in the form of sectional steel shape. Continuous fiber reinforced concrete : Concrete reinforced with CFRM. Continuous fiber prestressed concrete : Concrete reinforced by inducing prestress with CFRM. Capacity of CFRM: Maximum load that CFRM can sustain. Strength of CFRM: Value obtained by dividing the capacity of CFRM by the nominal cross-sectional area. Characteristic value of capacity of CFRM: Value for the capacity of CFRM which guarantees that the probability of tested capacity being below this value is within the specified limit based on

statistical interpretation of test results. Specified value of capacity of CFRM: Value for the capacity of CFRM which is specified by other design codes or specifications, apart from the characteristic value of capacity of CFRM. Guaranteed capacity of CFRM: Guaranteed capacity according to JSCE-E 131 "Quality Standards for Continuous Fiber Reinforcing Materials". Design capacity of CFRM: Value obtained by dividing the characteristic value of capacity of CFRM by the material factor. Characteristic value of ultimate strain of CFRM: Strain corresponding to the characteristic value of tensile capacity of CFRM. Design ultimate strain of CFRM: Value obtained by dividing the characteristic value of ultimate strain of CFRM by the material coefficient. Tensile rigidity of CFRM: Slope of the tensile force-strain curve for CFRM, when this curve is assumed to be linear. Young’s modulus of CFRM: Value obtained by dividing the tensile rigidity of CFRM by the nominal cross-sectional area. Nominal cross-sectional area of CFRM: Value obtained by dividing the volume of CFRM by the length. Bent section of CFRM: Section of CFRM set in a curved shaped by hardening with fiber binding material while continuous fibers are bent. May be in spiral form, stirrup form etc. Curved placement of CFRM: Placement of straight CFRM in a curved layout.

- 60 -

Creep failure: Failure due to progressive loss of tensile capacity over time, when CFRM is subjected to a continuous static tensile load. Creep failure capacity: Load-bearing capacity at time of creep failure. Flexural compressive failure: Form of failure in members subjected to flexure, whereby the compressed section of concrete fails before CFRM for main reinforcement break. Fiber breaking flexural failure: Form of failure in members subjected to flexure, whereby CFRM for main reinforcement break before failure of the compressed section of concrete. Fiber breaking shear failure: Form of shear failure in members subject to shear forces, whereby CFRM for shear reinforcement break. Tendon coating materials: Coating materials applied to tendons to prevent bonding with concrete. Tendon protection materials: Materials used to protect tendons from physicochemical deterioration due to external forces.

[COMMENT]: Definitions of shear reinforcement, hoop ties, spiral hoops, and tendons follow those given in JSCE Standard Specification (Design), where "steel" shall be taken to signify "CFRM". The nominal cross-sectional area of CFRM is obtained by dividing the volume of CFRM by the length. As volume generally includes elements not contributing to the strength of the reinforcement, the strength and Young’s modulus of CFRM, obtained using the nominal sectional area, are generally not equal to those of the continuous fiber itself.

- 61 -

CHAPTER 2: MATERIALS

2.1 GENERAL Materials to be used shall be of confirmed quality.

[COMMENT]: CFRM are new materials with limited field experience, and for some types little data on quality are available. It is therefore necessary to confirm the quality of the materials. In order to enhance the effectiveness in service of CFRM, it is particularly important to ensure that the concrete and any reinforcing or prestressing bars, anchoring devices, couplers, covering, protective materials, sheaths, grout etc. are of confirmed quality.

2.2 CONCRETE (1) Concrete shall have a design strength of not less than the values given in table 2.2.1 . Table 2.2.1

Minimum design strength of concrete

CFRM application

Minimum design strength

As substitute for reinforcing bars As prestressing materials

2

21 N/mm 2 30 N/mm

(2) Concrete quality shall be in accordance with chapter 2 of JSCE Standard Specification (Construction). (3) Quality of cement, water, fine aggregate, coarse aggregate, and admixtures used in concrete shall be in accordance with chapter 3 of JSCE Standard Specification (Construction).

[COMMENT]: When using CFRM as prestressing materials, greater compressive strength of concrete is required, as with conventional prestressed concrete structures. In structures where steel is not used and where there is no danger of corrosion of CFRM anchorages and couplers, the limitations on chloride contents in concrete given in JSCE Standard Specification + + (Construction) need not be applied. An excess of alkali ions such as Na and K , however, will tend to accelerate alkali-aggregate reaction, and appropriate methods should be taken to prevent alkali-aggregate reaction, for instance by eliminating reactive aggregate.

2.3 CONTINUOUS FIBER REINFORCING MATERIALS (1) CFRM used in construction shall normally be materials meeting the requirements given in JSCE-E 131 "Quality Standards for Continuous Fiber Reinforcing Materials".

- 62 -

(2) Where CFRM do not meet the requirements of JSCE-E 131 "Quality Standards for Continuous Fiber Reinforcing Materials" are to be used, tests must first be carried out to establish the design strength, design value of modulus of elasticity, design ultimate strain and method of use. (3) Where CFRM are to be subjected to heat treatment or other form of processing for anchoring, jointing, processing, assembly or placement, tests shall be performed to determine the level of quality loss due to the treatment, and an appropriate deign tensile strength and other design values shall be determined separately.

[COMMENTS]: (2) Tests shall be conducted according to JSCE-E 531 "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", and guaranteed values such as the tensile strength, modulus of elasticity and ultimate strain shall be determined based on the test results. Bonding strength shall be tested according to JSCE-E 539 "Test Method for Bond Strength of Continuous Fiber Reinforcing Materials by Pull-Out Testing". Flexural tensile failure strength, creep failure strength, relaxation, fatigue strength, coefficient of thermal expansion, alkali resistance, and shear strength shall be determined using test methods meeting JSCE standards. Values determined using well-established alternative test methods, however, may also be used provided a reliable guaranteed value allowing for the effect of anchorage is obtained. (3) See section 3.3 below for details of treatment and handling for heat treatment or other forms of processing.

2.4 REINFORCING BARS (1) Where CFRM are to be used in conjunction with reinforcing bars, the bars shall be selected to conform to the intended purpose of the CFRM. (2) Where CFRM are to be used to enhance the corrosion resistance of a structure, epoxy-coated reinforcing bars used in conjunction with the CFRM shall conform to JSCE-E 102 "Quality Standards for Epoxy-Coated Reinforcing Steel Bars". (3) Where ordinary reinforcing bars without corrosion-proofing are to be used, section 3.7.1 of JSCE Standard Specification (Construction) shall be adhered to.

[COMMENTS]: (1) CFRM are used mainly for their corrosion-resistant and non-magnetic properties, therefore reinforcing bars used in conjunction with CFRM must be selected in accordance with the intended purpose. It should be noted in this connection that non-magnetic reinforcing bars have also been developed in recent years. (2) The material properties of CFRM tend to lead to their being used in harsh, saline environments etc., thus epoxy-coated reinforcing bars are prescribed as standard for use in conjunction with CFRM, in order to ensure corrosion protection. Galvanized reinforcing bars could also be considered, but owing to the lack of experience with this in combination with CFRM, epoxy-coated reinforcing bars have been preferred here. (3) Where ordinary unprotected reinforcing bars are used, the prescription given in section 3.7.1 of

- 63 -

JSCE Standard Specification (Construction) of conformity with JIS G 3112 "Steel Bars for Concrete Reinforcement" must be adhered to. Stainless and corrosion-proof reinforcing bars have been developed in recent years. Where these or non-magnetic reinforcing bars re to be used, they must first be confirmed to have performance equivalent to the JIS standard quoted above.

2.5 PRESTRESSING STEEL Where prestressing steel is to be used, section 3.7.2 of JSCE Standard Specification (Construction) shall be adhered to.

[COMMENT]: Where ordinary prestressing steel without corrosion-proofing is to be used, the requirements of section 3.7.2 of JSCE Standard Specification (Construction) are to be applied as-is; this means prestressing steel must generally conform to JIS G 3109 "Steel Bars for Prestressed Concrete", JIS G 3137 "Small Size Deformed Steel Bars for Prestressed Concrete", and JIS G 3536 "Uncoated Stress-relieved Steel Wires and Strands for Prestressed Concrete". Corrosion-proofed or stainless prestressing steels have been developed in recent years. Where these steels are to be used, they must first be confirmed to have performance equivalent to the JIS standards quoted above, and, additionally, the effectiveness of their corrosion-proofing must be adequately assessed.

2.6 ANCHORAGES AND COUPLERS (1) Anchorages and couplers shall be of a structure and strength such that they do not fail below the guaranteed capacity or undergo significant deformation.

(2) Materials used in anchorages and couplers shall be of confirmed quality. (3) Anchorages and couplers shall be tested for performance according to JCSE-E 537 " Test Method for Performance of Anchorages and Couplers in Prestressed Concrete using Continuous Fiber Reinforcing Materials".

[COMMENTS]: (1) Anchorages or couplers shall be of a structure and strength corresponding to or superior to the anchoring or coupling system using CFRM, allowing for safety during prestressing work, the need to prevent excessive set in anchorage etc. The guaranteed capacity of the anchorages or couplers, and the guaranteed capacity of the tendons, are treated separately here. The reason for this is that the tensile strength of CFRM is evaluated allowing for the effects of the anchorages, while in many cases the anchoring device does not allow the CFRM to exert its full tensile strength, and in multi-cables especially, the fall-off is significant. "Anchoring or coupling system using CFRM" here refer respectively to systems configured with CFRM and anchorages, and CFRM and couplers. (2) "Materials used in anchorages and couplers" refers to synthetic resins, anchoring expansion agents,

- 64 -

grout, anchor bars etc. As these are the most important materials in anchoring and coupling of prestressed concrete structures, they must be of proven, reliable quality and outstanding durability. (3) Performance testing of anchorages and couplers may be carried out according to JSCE-E 537. This test, however, is intended for new types or types for which adequate test data is not available; testing may be omitted for types of proven quality and reliability. for which test data is given in the Documentation section of this Recommendation.

2.7 SHEATHS (1) Sheaths shall be of a type not easily deformed during handling or concrete placement, and capable of withstanding intrusion of cement paste at laps and joints. (2) Sheaths should be preferably have low friction with tendons, and should not cause damage to tendons during tensioning. (3) The effects of the sheaths on the structure must be fully known.

[COMMENTS]: (1) Bonding between CFRM and prestressed concrete grout, or between sheaths and concrete, may or may not be factored into the design, therefore the sheath material and geometry must give the performance intended in the design. Plastic sheaths may be used, in addition to conventional steel sheaths. Plastic sheaths must be sufficiently rigid to prevent any hindrance of placement etc. Severe deformation of sheaths or leakage of cement paste may hinder or prevent prestressing work, therefore the use of non-rigid or damaged sheaths must be avoided. (3) The bonding characteristics of the intended sheaths with concrete and grout, and the effects on the structure of cracking, differences in coefficients of thermal expansion etc. must be fully known in advance. Details of handling of sheaths are given in section 3.3.4 below.

2.8 TENDON COATING MATERIALS AND TENDON PROTECTION MATERIALS (1) Materials used for tendon coating shall not cause damage to CFRM tendons or to the concrete, and shall not cause bonding between CFRM tendons and the concrete during prestressing. (2) Tendon protection materials shall protect CFRM tendons fully from damage due to external factors.

[COMMENT]: Tendon coating materials are used to prevent bonding between CFRM tendons and concrete, whereas tendon protection materials are used to protect CFRM tendons from physicochemical deterioration due to external factors, hence the distinction drawn here between the two types of material. Both types should of course fulfill their intended purpose, and the materials used must be of guaranteed durability and quality.

- 65 -

2.9 GROUT FOR PRESTRESSED CONCRETE (1) Grout for prestressed concrete shall be of sufficient quality to protect the tendons and to form a monolithic structure by bonding with the member concrete and the tendons. (2) The quality and materials of cement grout for prestressed concrete shall satisfy the following conditions. (a) Consistency: The consistency shall be set at a level appropriate for the construction, taking into account the length and shape of the sheaths and ducts, construction season and weather conditions, type of tendon and the proportion of the sectional area of the prestressing steel to that of the duct. (b) Bleeding rate: The bleeding rate shall be not more than 3%, and preferably not more than 1%. (c) Expansion rate: The expansion rate shall be not more than 10%. The expansion rate after grouting shall exceed the bleeding rate until maximum bleeding is reached. The standard time from the completion of agitation to the completion of grouting should be around 30 minutes. 2

(d) Strength: Compressive strength at 28 days shall be not less than 20 N/mm . (e) Water-cement ratio: The water-cement ratio of the grout shall be not more than 45%. (f) Cement: Cement used for grouting shall comply with JIS R 5210. (g) Water: Water used for grouting shall not contain harmful levels of substances adversely affecting the grout or the prestressing tendons. (h) Admixtures: The advisability of using admixtures, and the quality and method of use of the admixtures, shall be studied in advance. (3) Grout for prestressed concrete other than that specified in (2) above shall first be checked for quality and the method of use adequately studied.

[COMMENTS]: (1) The purpose of grouting is to protect the tendons and to create a monolithic structure through bonding of member concrete and tendons. The grout must therefore fill ducts completely, and surround the tendons. The grout must therefore maintain good fluidity and workability up to the completion of grouting, with minimum bleeding, proper expansion after grouting, and adequate strength. Grouting should ideally be carried out from below, causing the grout to flow gradually upwards. Where tendons are placed with multiple bend-ups and bend-downs, grout will shift from higher levels to lower levels, therefore the use of high quality grout with little or no bleeding is advised. Further, if the gap between sheaths and tendons is too narrow, it will not be properly grouted, therefore the use of large-diameter sheaths and high quality grout is advised. (2) High-quality grouts are now available with superplasticizers in place of conventional plasticizers, giving little or no bleeding, and maintaining initial levels of fluidity for long periods while at the same time giving high viscosity. The water-cement ratio should be kept as low as possible given the fluidity requirements. A high water-cement ratio will cause loss of strength and bonding, and incomplete grouting of ducts due to bleeding and shrinkage. Conversely, a low water-cement ratio will result in high viscosity and poor

- 66 -

workability. The standard water-cement ratio is therefore given as 45%. The use of recently developed superplasticizers allows the water-cement ratio to be reduced while giving a grout with high fluidity and workability. (3) The use of cement-based grout may be inadvisable in certain circumstances owing to adverse effects on durability of CFRM tendons. In such cases, tests should be carried to check that the grout meets the required quality standards.

- 67 -

CHAPTER 3: CONSTRUCTION

3.1 GENERAL (1) Handling and storage of materials, assembly and placement of CFRM and steel, placement of concrete, prestressing and grouting of prestressed concrete shall be carried out in the order given in the construction plan, and following the prescribed procedures. (2) For the construction of concrete structures, engineers having sufficient knowledge of concrete construction shall be present on site.

[COMMENT]: (2) "Engineers having sufficient knowledge of concrete construction" (concrete specialists) shall be construed as Concrete engineers or Chief Concrete Engineers authorized by the Japan Concrete Institute, Prestressed Concrete Engineers authorized by the Prestressed Concrete Technology Association, or other engineers with similar or superior specialist skills. The presence of such engineers on site to supervise construction appropriately is extremely important in obtaining the desired quality of concrete. For particularly important structures, it is recommended that such engineers be stationed permanently on site.

3.2 HANDLING AND STORAGE OF MATERIALS (1) CFRM shall be handled carefully to prevent any damage to the surface. (2) When storing CFRM outdoors, placing them directly on the ground should be avoided, and a suitable cover shall be provided. CFRM should also not be placed directly on the ground when stored in storehouses, and if necessary suitable covers should be provided. Environmental factors such as high temperature, ultraviolet rays, chemical substances etc. deleterious to CFRM should be eliminated, and the CFRM shall be stored in such a manner as to prevent damage or deformation. (3) Anchorages, couplers and materials used in anchorages and couplers shall be stored in a storehouse, free from dust and protected from damage, deformation or deterioration.

[COMMENTS]: (1) CFRM are generally made with a matrix of synthetic resin, rendering them liable to surface damage. Deep scoring by sharp steel edges etc. will significantly reduce their failure load, possibly resulting in serious accidents especially when the CFRM are used as tendons. Scoring of the surface of glass fiber based CFRM may cause loss of durability due to infiltration of alkalis through the damaged areas, therefore care is advised in the handling of these materials also. (2) Storage of CFRM directly on earth or concrete, whether outdoors or in a storehouse etc., increases the likelihood of damage or loss of quality, and such locations should be avoided. High temperatures, ultraviolet rays, chemical substances etc. are also deleterious to CFRM, and these factors too should be

- 68 -

eliminated. CFRM must be stored in an environment free from possible sources of damage. CFRM shipped in coil form should be stored in such a way that harmful kinks etc. do not develop when the coil is unwound. (3) Anchorages, couplers and materials used in anchorages and couplers are important elements in prestressed concrete, therefore storage in a storehouse is prescribed. Parts destined to be in contact with concrete or grout must also be kept free from grease, dirt, dust etc. to ensure full bond strength.

3.3 PREPARATION, ASSEMBLY AND PLACEMENT OF CFRM TENDONS, CFRM REINFORCEMENT ETC. 3.3.1 Preparation and assembly of CFRM tendons (1) CFRM tendons shall be prepared and assembled in such as way as to give the configuration and dimensions specified in the design, while avoiding any damage to the material. Any CFRM tendons found to be damaged on the surface, bent, subjected to high temperatures or stored out of doors for long periods shall be discarded. (2) CFRM tendons shall in general not be bent. Where bending is unavoidable, this shall be done in a workshop using techniques that do not damage the material. The tensile strength of CFRM tendons after bending shall be confirmed using appropriate testing methods. (3) CFRM tendons used in pretensioning, and CFRM tendons required to bond, shall be cleared of any oil, grease or foreign matter likely to impair bonding prior to assembly.

[COMMENTS]: (1) CFRM tendons must be correctly formed into the configuration and dimensions specified in the design, without damaging the material. Cutting of CFRM tendons, preparation for anchoring or fitting of anchorages etc. should be carried out according to the proper method for CFRM tendons. CFRM tendons should be cut using an efficient high-speed rotatory grinder or similar manner whic h does not damage the material. CFRM tendons which are bent or have surface damage must not be used, as there is a possibility of severe loss of tensile strength. CFRM tendons which have been subjected to high temperatures should also not be used, as the thermal deterioration of the resins causes loss of fiber binding performance, which could result in loss of tensile strength. Depending on the type of CFRM tendons, long exposure to direct sunlight may result in deterioration due to ultraviolet rays, therefore CFRM tendons stored out of doors for long periods should not be used. (2) The fiber binding material in CFRM tendons is generally a thermosetting resin, and bending such a material on site while maintaining the required quality is technically difficult. Therefore, CFRM tendons should generally not be bent. If bending of CFRM tendons is unavoidable, this should be done in a workshop following methods which do not damage the material. As the tensile strength of CFRM tendons is thought to be reduced by bending and according to the bending radius, the tensile strength

- 69 -

should be confirmed by appropriate methods reconstructing the actual conditions of use, and checked against the design conditions. (3) Foreign matter such as grease, paint and dirt may impair the bonding between concrete or grout and CFRM tendons, resulting in slippage of tendons. The surface of CFRM tendons must therefore be thoroughly cleaned before use.

3.3.2 Preparation and assembly of CFRM reinforcement (1) CFRM reinforcement shall be prepared and assembled following methods which do not damage the material, so as to conform to the configuration and dimensions given in the design. Any CFRM reinforcement found to be damaged on the surface, bent, subjected to high temperatures or stored out of doors for long periods shall be discarded. (2) Bending of CFRM reinforcement shall normally be done in a workshop, following methods which do not damage the material. (3) Where the bending radius of the CFRM reinforcement is not given in the design, the bending radius and bending method shall be determined on the basis of tests conducted to confirm that the tensile strength required in the design is met. (4) CFRM reinforcement shall be cleared of any oil, grease or foreign matter likely to impair bonding prior to assembly.

[COMMENTS]: (1) CFRM reinforcement must be handled similar to the case of CFRM tendons according to the comment of section 3.3.1(1). (2) For the same reason as that given in the comment of section 3.3.1(2), bending of CFRM reinforcement such as stirrups and spiral reinforcement shall normally be done in a workshop. Certain types of CFRM reinforcement may be bent and thermoset on site, or bent by heating on site using thermoplastic resins, but the tensile strength of CFRM reinforcement bent in this way must still be confirmed by appropriate testing methods. (3) The tensile strength of bent CFRM reinforcement is known to be reduced by the bending process, but the level of strength loss depends on the type of continuous fiber, the manufacturing process of the reinforcement, the bending radius etc. The bending radius and method of bending must therefore be determined based on tests to confirm the extent of loss of tensile capacity, and the bending radius should be made as large as possible. (4) See the comment of section 3.3.1(3).

3.3.3 Duct manufacture The materials and methods used in duct manufacture shall not be injurious to CFRM tendons, reinforcement or concrete.

- 70 -

[COMMENT]: Materials used in duct manufacture must be confirmed not to erode CFRM tendons or reinforcement, or to cause deterioration of concrete, prior to use. The manufacturing method must not cause cracking in concrete, significant increase in friction during prestressing, or damage to CFRM tendons. Where subsequent bonding is required, the concrete and CFRM tendons must act as a monolithic body, therefore a high level of bonding between the duct and the concrete or grout.

3.3.4 Placement of sheaths and CFRM tendons (1) Damaged sheaths or sheaths with severe internal rusting shall not be used. Joints of sheaths shall be securely sealed to prevent penetration of cement paste during concreting. (2) Sheaths and CFRM tendons shall be firmly supported at the required positions and in the required directions by methods not injurious to the material, and placed correctly to ensure their position and configuration remain unchanged during concrete placement. The bending radius of bent CFRM tendons shall be determined so as not to impair the tendon. (3) CFRM tendons shall be placed in sheaths without any entanglement. (4) CFRM tendons used in pretensioning shall be protected from damage due to contact with end forms. Unbonded CFRM tendons shall be carefully installed without any damage to the coatings. (5) Sheaths and CFRM tendons shall be inspected after placement, and corrective measures such as repair or replacement shall be taken in the event of damage or dislocation being found. (6) Tolerances for placement positions of CFRM tendons shall be determined within a range not affecting the members, and allowing for factors such as the size of the members.

[COMMENTS]: (1) Steel sheaths with significant internal rusting must not be used. This is not only because of the increased friction during prestressing, but also because of possible damage to CFRM tendons and impairment of bonding. Foreign matter such as grease and loose rust likely to impair bonding shall be removed from the interior of the sheath before use. Incomplete jointing between sheaths, between sheaths and anchorages, or between sheaths and couplers connectors may cause cement paste to leak into the sheath during concreting, leading to bonding impairment similar to that described in relation to damaged sheaths. The joints must be protected from ingression of cement paste by extending the lap, winding with insulating tape etc. It is important to prevent corrosion of sheaths at anchorage ends by application of rust-preventive agents or similar treatment. In order to prevent damage to CFRM tendons within the sheath, plastic sheaths etc. may be used, but their performance must be thoroughly evaluated first .

- 71 -

(2) If CFRM tendons are not maintained in their proper positions, the required prestress cannot be introduced into the concrete even if the specified tensile force is applied to CFRM tendons. CFRM tendons must therefore be accurately placed in each position. CFRM tendons and sheaths must be firmly fixed using adequate supports placed at relatively short intervals, so that CFRM tendons and sheaths can resist the weight of fresh concrete and strong vibration caused by the vibrators during concreting. The spacing of the supports must be determined according to the types and rigidities of CFRM tendons and sheaths, allowing for the friction coefficient assumed in the design. Where the bending radius of CFRM tendons is small, local stresses will be set up in CFRM tendons, causing loss of tensile strength. When straight CFRM tendons are bent into position, the minimum radius to which CFRM tendons can be bent by elastic deformation without causing damage must first be ascertained by testing. The minimum bending radius when sheaths are used should preferably by either 5 m or 100 times the sheath diameter, whichever is the greater. This is the minimum radius hitherto confirmed in tests. No useful data is yet available regarding minimum values when sheaths are not used, and loss of tensile strength must be checked by testing etc. As the loss of tensile strength varies depending on the type of CFRM tendons, testing is necessary in any case. When CFRM tendons are used as external cables, significant local stress is applied to the deviators where CFRM tendons are bent up, and determination of the bending radius, selection of sheath and wadding material etc. must be done after thorough safety testing etc. (3) When multiple CFRM tendons are placed in a sheath, entangling not only increases friction during prestressing, there is also a possibility of uneven stressing in CFRM tendons. Suitable spacers should therefore be used to ensure CFRM tendons are parallel within the sheath. (4) In pretensioning, CFRM tendons installed via placement holes in the end forms may fail when they are subjected to damage due to contact with the placement hole during prestressing or compacting of concrete. Measures must therefore be taken to prevent CFRM tendons from contacting the form directly, for instance by using wadding material in the placement holes. CFRM tendons used in unbonded prestressing structures are generally protected by coating materials. If the coating materials are stripped off or damaged, insulation from the concrete is impaired and prestressing work becomes more difficult with possible loss of tensile strength of CFRM tendons. Corrective action must be taken in the event of stripping or damage of coating materials. (5) Any dislocation or damage of sheaths or CFRM tendons during placement must of course be corrected during the installation work. Post-installation concreting work must also be attended by careful inspection and repair if necessary. (6) Installation tolerances vary depending on the size of the members or the arrangement of CFRM tendons. Generally, the tolerance of the tendon centroid shall be not more than 5 mm when the member size is less than 1 m, and the lesser of 1/200 of the member size and 10 mm when the member size is equal to or greater than 1 m. If the error is greater than 10 mm, corrective action shall be taken.

3.3.5 Assembly and placement of anchorages and couplers

- 72 -

(1) Anchorages and couplers shall be assembled accurately in the configuration and dimensions specified in the design documents, and shall be properly installed in the location and direction specified in the design. Anchorages and couplers, and reinforcement in their vicinity, shall be corrosion-proofed if necessary. (2) The bearing surface of the anchorage shall be installed perpendicular to CFRM tendons. Anchoring of CFRM tendons to the anchorages shall be carried out according to the prescribed procedures, and due care shall be taken to prevent any damage to CFRM tendons at the anchorage, or loss of anchoring capacity. (3) When CFRM tendons are coupled, the couplers shall have sufficient capacity and corrosion-proofing, and the pulling side of the coupler shall be allowed adequate movement to apply tension to CFRM tendons. (4) After the placement of the anchorages, an inspection shall be made, and damaged hardware shall be replaced or repaired. Dislocation of the hardware shall also be corrected.

[COMMENTS]: (1) and (4): Anchorages are subject to tremendous forces, and their proper assembly and placement following the design drawings is important to ensure proper transfer of stresses and to avoid accidents. With current technology, the use of metal anchorages and couplers is unavoidable, thus proper corrosion-proofing is required to prevent loss of structure durability due to corrosion. (2) If the bearing surfaces of anchorages are not placed perpendicularly to CFRM tendons, local bending of CFRM tendons during tensioning or anchoring may result. This local bending could lead to failure of CFRM tendons, or prevent the completion of anchoring work. The anchorages and tendons must therefore be installed perpendicularly to each other, and a straight portion of a certain length should be allowed in CFRM tendons around the anchorages. As the anchoring methods used with CFRM tendons vary according to the construction technique, the prescriptions for anchoring given for each technique must be followed. The use of inappropriate anchoring methods could prove fatal for prestressed concrete structures, therefore proper technical controls on anchoring work must be enforced. (3) When CFRM tendons are coupled, the couplers must be corrosion-proofed to prevent loss of member durability. The movement of the couplers during tensioning must be calculated and a sufficient space for the movement must be provided on the tensioning side of the couplers. The positions of joints must be checked after assembly of couplers.

3.4 CONCRETING (1) Batching, mixing, transportation, placing, curing, surface finishing etc. of concrete shall be carried out according to the prescribed procedures. (2) Casting and compaction of concrete shall be carried out taking due care to avoid disturbing the

- 73 -

placement of CFRM, reinforcing bars, anchorages, sheaths etc., avoiding damage to CFRM and ensuring full concreting of all areas around CFRM and reinforcing bars, anchorages, sheaths etc. (3) Steam curing shall be performed following thorough assessment of the temperature characteristics of CFRM, anchorages, couplers etc. used, setting the curing temperature accordingly.

[COMMENTS]: The general remarkable points for concreting are given in JSCE Standard Specification (Construction). Batching and mixing are covered in chapter 5 of JSCE Standard Specification (Construction), transportation and placing in chapter 7, curing in chapter 8 and surface finishing in chapter 12. Each of these chapters is followed here. In addition, the smaller member dimensions and higher strength of concrete are used in prestressed concrete structures as compared to normal reinforced concrete structures, therefore particular caution is advised during placement because of the use of different quality concrete from that used in reinforced concrete structures. (2) In prestressed concrete, there is a danger of displacing not only CFRM and reinforcing bars and forms, but also anchorages and sheaths, therefore operations must be carried out with caution. It should be borne in mind that the lower weight and rigidity of CFRM in comparison to reinforcing bars renders it more liable to displacement due to buoyancy. Reinforcing-bar workers should stay during concrete placement work to correct any dislocation of CFRM or reinforcing bars, anchorages, sheaths etc. CFRM may be damaged by direct contact with an internal vibrator, therefore the use of internal vibrators protected with polyurethane etc. is recommended. (3) Certain types of CFRM , anchorages, couplers, sheaths etc. exhibit material quality change under steam curing temperatures, hence this provision is made. Particular care must be taken with regard to the increased relaxation and loss of bond strength in CFRM at high temperatures. When steam curing is used, heating should begin after not less than three hours after concrete placement, and the rate of temperature increase shall generally be not more than 15°C per hour. The curing temperature shall be not more than 65°C, and the temperature shall be low enough to avoid impairing the quality of CFRM and the anchorages or couplers.

3.5 PRESTRESSING (1) The tensile forces to be applied to CFRM tendons in prestressing, the method of prestressing, safety measures during prestressing, method of calibration of the tensioning apparatus, minimum concrete strength for prestressing, and methods of prestressing control shall be determined according to the prescribed procedures. (2) The coefficient of friction and apparent modulus of elasticity applied in control of prestressing work shall generally be determined based on prestressing tests on site. (3) The coefficients of friction of the tensioning apparatus and the anchorages shall also be determined based on testing.

- 74 -

(4) Tendons shall be anchored to ensure that all the constituent CFRM tendons are subjected to the required tensile force.

[COMMENTS]: Prestressing work is covered in section 27.6 of JSCE Standard Specification (Construction), which is also applied here. For the techniques given in the Documentation section of this Recommendation, the control methods given for each technique shall be adhered to. (1) Since the elongation of CFRM tendons is greater for a given prestressing level than the elongation of prestressing steel, use of a jack with a long stroke, use of a succession of different jacks etc. must be considered. (2) Measurements of the coefficient of friction and apparent modulus of elasticity shall be made at the start of work, and redone if any anomalies are found during control of prestressing work. Control of prestressing may be carried out based on the measured coefficient of friction µ. The tolerances for µ given in Table 27.6.1 in the comment to section 27.6.4 of JSCE Standard Specification (Construction) relate to prestressing steel only. For CFRM tendons, tolerances of way as those for prestressing steel.

µ must

be calculated in the same

(4) For CFRM tendons, the stress - strain curve is linear with no yielding, and the ultimate strain is lower than that for prestressing steel. Further, as the strength loss in CFRM tendons due to bending is greater than in steel, tensioning of CFRM tendons and anchoring to the anchorage must be carried out carefully to avoid brittle failure. This will require initial alignment of parts exerting tensile force on each CFRM tendons and monitoring of extension during prestressing to be enforced more strictly than is generally the case for prestressing steel. Prestressing of CFRM tendons must be carried gradually, avoiding sudden increases in tensile force. The amount of slipping when anchoring CFRM tendons can be greater than with prestressing steel, but owing to the lower tensile rigidity, the reduction in tensile force in CFRM tendons due to slipping in the anchorages is generally less.

3.6 GROUTING (1) Where integration of member concrete and CFRM tendons by grouting is required, grouting shall be carried out immediately after the completion of prestressing. (2) Selection of grouting tools, batching, mixing, agitation, injection, requirements for work in hot or cold weather etc. shall be according to the prescribed procedures.

[COMMENT]: For cement-based grout, specification(1) is given in the section of 27.7.1 and specifications(2) is given in the section of 27.7.2~27.7.6 of JSCE Standard Specification (Construction) and these specifications should be followed here. For non-cement grouts, suitable working procedures should be applied allowing for the differing characteristics of the materials, based on the above.

- 75 -

CHAPTER 4: QUALITY CONTROL AND INSPECTION

4.1 GENERAL The necessary quality control and inspections of concrete materials, CFRM, steel used in conjunction with CFRM, other materials, equipment, working procedures and completed structures shall be carried out to ensure the safe and economic construction of continuous fiber reinforced concrete structures of the required quality.

[COMMENT]: Quality control when using CFRM is equally as important as when conventional materials are used (c.f. the comment of section 13.1 of JSCE Standard Specification (Construction).

4.2 TESTS 4.2.1 General Quality control shall be carried out by te sting of materials, equipment and machinery according to the prescribed methods, in order to ascertain their performance. Testing of CFRM shall generally be carried out according to this Recommendation.

[COMMENT]: General provisions for quality control methods are given in the comments of section 13.1 and 13.2 of JSCE Standard Specification (Construction), but as JIS standards for testing of CFRM are not available, this Recommendation has been adopted as standard.

4.2.2 Tests for Concrete The performance of concrete before and after work, and if necessary also during work, shall be tested according to the prescribed methods.

[COMMENT]: Tests for quality control of concrete are given in section 13.5 and 27.10.1 of JSCE Standard Specification (Construction), and these specifications are followed here. As noted in the comments of section 2.2 above, in structures where CFRM are not used in conjunction with steel and where there is no possibility of corrosion of anchorages and couplers, the requirements for chloride contents in concrete given in JSCE Standard Specification (Construction) need not be applied. Contents of chloride ions in concrete must still be tested and kept within strict limits in order to prevent deterioration of the concrete itself due to alkali-aggregate reaction etc.

4.2.3 Tests for CFRM tendons

- 76 -

(1) Quality tests shall be conducted on CFRM tendons prior to use, in order to ensure the required performance. Quality testing shall cover the following items: (a) Tensile strength (or maximum tensile load); tensile modulus of elasticity (or tensile rigidity), and ultimate strain; (b) Fatigue strength; (c) Relaxation rate; (d) Bond strength; (e) Coefficient of thermal expansion; (f) Other The above tests may be dispensed with for materials of proven quality and performance. (2) Quality of tensioning systems using CFRM tendons shall generally be tested for the whole system including anchorages and couplers, with quality testing carried out before use to ascertain performance. Quality testing shall cover the following items: (a) Tensile strength (or tensile load); tensile Young’s modulus (or tensile rigidity); (b) Fatigue strength; (c) Relaxation rate The above tests may be dispensed with for materials of proven quality and performance.

[COMMENTS]: The handling of CFRM is generally very different from that of steel in terms of mechanical properties, durability and handling method, and quality controls must be implemented allowing for these differences. (1) These tests are required to control the performance of CFRM tendons themselves; bond strength testing may be omitted for CFRM tendons to be used unbonded. "Other" tests refers to accelerated deterioration testing in high temperatures, alkaline or acid conditions, creep failure testing etc. Such tests shall be performed if necessary to ascertain quality. Quality control through these tests is extremely important, but it normally requires special, precision testing equipment, extensive expertise in measurement and / or long periods of time. Adoption of manufacturers' guaranteed values has therefore been allowed where performance has been checked by suitable testing prior to shipment, and where the suitability of transportation methods has been confirmed. If there is a possibility of mishandling during shipment or of significant damage due to long periods of storage, however, the materials must not be used without first being tested, even in the absence of any visible damage. This shall also apply to materials during work; materials suspected of having suffered damage shall immediately be replaced and tested. Possible factors affecting CFRM before and during work are given below. -Factors affecting CFRM before start of work: Bending beyond prescribed limits, subjection to shocks, dragging etc. during transportation; temperature, humidity, dampness or direct sunlight

(ultraviolet rays) during storage; welding sparks, chemicals etc. -Factors affecting CFRM during work: Bending or impact force beyond allowed limits during placement; over-tight binding, welding sparks, chemicals, excessively high temperatures during curing

- 77 -

etc. (2) The mechanical properties of CFRM tendons are significantly affected by the anchorages and couplers, and there is a tendency for systems as a whole to give lower performance than either single or multiple tendons alone. When using CFRM tendons, therefore, tests must be carried out on factors likely to be affected when anchorages and couplers are used in a complete system, in order to ascertain performance. These tests may be dispensed with for CFRM tendons of proven quality used in conjunction with anchorages and couplers of guaranteed quality and known performance, which are specified in the Documentation section of this Recommendation as being designed expressly for use with CFRM tendons in question.

4.2.4 Tests for anchorages and couplers Anchorages and couplers for use with CFRM tendons shall be tested for quality before use. Such tests may be dispensed with for materials of proven quality.

[COMMENT]: The geometry, performance, service conditions etc. of anchorages and couplers vary significantly for different types, and also depending on the type of CFRM tendons they are used with. Such anchorages and couplers must therefore be tested following an appropriate method capable of reproducing the service conditions and expected tensile forces. Tests must confirm that the strength and structure of the materials are such that failure or significant deformation do not occur below the guaranteed tensile load, and that the required anchoring or coupling effect is achieved with the proposed CFRM tendons. Standard test methods for anchorages and couplers are given in JSCE-E 537 "Test Method for Performance of Anchorages and Couplers in Prestressed Concrete using Contin uous Fiber Reinforcing Materials", and these test methods may be followed here. Depending on the type of anchorages and couplers, it is also important to check that set loss due to tendon slippage is within allowable limits; furthermore, given that continuous fiber reinforced concrete structures are often located in extreme environments, any steel anchorages and couplers must also be confirmed to be sufficiently durable for the environment. Such tests may be dispensed with for materials of proven quality which are given in the Documentation section of this Recommendation.

4.2.5 Tests for other materials used in continuous fiber prestressed concrete Materials used in anchorages and couplers, sheaths, tendon coating and protection materials, grout etc. shall be quality tested before use to ascertain their performance. Such tests may be dispensed with for materials of proven quality.

[COMMENT]: The materials listed here must be tested according to appropriate methods to ensure they have no adverse physicochemical effect on CFRM tendons, and that they give the required performance.

- 78 -

For sheaths, in addition to testing according to section 27.10.4 of JSCE Standard Specification (Construction), the frictional force arising between sheaths and tendons must also be tested by methods capable of adequately reproducing service conditions, as the surface configurations of CFRM tendons are very varied. Where plastic or other non-conventional, non-steel sheaths are to used, bonding characteristics with concrete and grout, thermal characteristics, durability etc. must also be ascertained by testing prior to use, in order to ensure the required performance is achieved in the structure. Monitoring by tests for grout is covered in section 27.10.6 of JSCE Standard Specification (Construction), and this specification is followed here. Where non-cement grouts are used, further testing of bonding characteristics, thermal characteristics, and durability will also be required, in addition to the tests given in this Standard Specification.

4.2.6 Tests for CFRM reinforcement (1) Quality tests shall be conducted on CFRM reinforcement prior to use, in order to ensure the required performance. Quality tests shall cover the following items: (a) Tensile strength (or maximum tensile load); tensile modulus of elasticity (or tensile rigidity), and ultimate strain; (b) Fatigue strength; (c) Bond strength; (d) Coefficient of thermal expansion; (e) Other The above tests may be dispensed with for materials of proven quality and performance.

[COMMENT]: Tests of CFRM reinforcement is broadly similar to that for CFRM tendons, covered in section 4.2.3 above, with the exception of relaxation test, omitted here as necessary only for tendons. .

4.2.7 Testing for other materials for use with continuous fiber reinforced concrete Steel reinforcement etc. for use with CFRM in concrete shall be tested at the required times following the prescribed methods to confirm performance.

[COMMENT]: Tests for monitoring of reinforcing bars, their joints, prestressing steels, their anchorages and couplers, prestressing steel sheaths, spliced materials, friction-reducing agents etc. used in conjunction with CFRM are covered in chapters 13 and 27 of JSCE Standard Specification (Construction) and this specification is followed here. Testing of epoxy-coated reinforcing bars used in conjunction with CFRM shall follow chapter 2 of JSCE "Recommendations for Design and Construction of Reinforced Concrete Structures using Epoxy-Coated Reinforcing Steel Bars", .

- 79 -

4.3 INSPECTION OF STRUCTURES Inspection of structures shall be conducted after the completion of concrete structures.

[COMMENT]: Continuous fiber reinforced concrete structures are frequently located in harsh environments, and in such cases, more detailed inspection in preparation for future maintenance should be carried out, as outlined in the comments of section 13.9.1 of JSCE Standard Specification (Construction). When the loading test is necessary to confirm the safety of structures, the method should be followed in section 13.9.1 of JSCE Standard Specification (Construction).

4.4 CONSTRUCTION RECORDS The construction program, working conditions, curing methods, meteorological conditions, air temperature, quality controls and inspections, structural inspections etc. shall be recorded during the construction as the circumstances demand. Construction records shall be retained in the long term.

[COMMENT]: CFRM are generally more resistant to chloride ion corrosion than conventional steel, giving continuous fiber reinforced structures superior durability. In the longer term, however, CFRM may undergo complex forms of deterioration in various environments, either independently or through compound interaction with concrete. As stated in the comments of section 14.1 of JSCE Standard Specification (Construction), the keeping and preservation of construction records provides essential information for future maintenance of continuous fiber reinforced concrete structures.

- 80 -

QUALITY SPECIFICATIONS FOR CONTINUOUS FIBER REINFORCING MATERIALS 1. SCOPE These specifications shall apply to continuous fiber reinforcing materials used for reinforcement or prestressing tendons in concrete.

2. REPRESENTATION The following items shall be included in the representation of specifications. Item 14) "Relaxation rate" may be excluded for materials intended for use as reinforcement only. Calculation methods for each category are given in section 8. below. 1) Fiber category and identification 2) Configuration and identification 3) Binding material 4) Strength and modulus of elasticity 5) Volume ratio of axial fiber 6) Nominal cross sectional area 7) Nominal diameter 8) Maximum size 9) Nominal mass density 10) Guaranteed capacity 11) Tensile rigidity 12) Elongation 13) Creep failure capacity 14) Relaxation rate

3. CATEGORY, IDENTIFICATION, DESIGNATION 3.1 Fiber type and identification Five categories of fiber may be used in CFRMs, with identification symbols as given in Table 1.

Table 1: Fiber type and identification Fiber type

Identification

Carbon fiber

C

Aramid fiber

A

Glass fiber

G

Vinylon fiber

V

Composite

*)

*) two letters of two fibers with the first letter indicating a dominant fiber content. eg. GC (glass fiber and carbon fiber composite with a larger volume of glass fiber) - 81 -

3.2 Configuration and identification Configuration of CFRMs is categorized as one of the five types, with identification symbols as given in Table 2.

Table 2: Configuration categories and identification symbols Category Symbol

Rod

Strand

R,D *)

S

Braided B

Lattice

Rectangular

L

P

Configuration

*) D = deformed

3.3 Designations Designations for CFRM fiber / configuration combinations are given in Table 3.

Table 3: Designations Fiber type

Carbon

Aramid

Glass fiber

Vinylon

Composite

Configuration Rod Strand Braided Lattice Rectangular Rod Strand Braided Lattice Rectangular Rod Strand Braided Lattice Rectangular Rod Strand Braided Lattice Rectangular Rod Strand Braided Lattice Rectangular

Designation CR,CD CS CB CL CP AR,AD AS AB AL AP GR,GD GS GB GL GP VR,VD VS VB VL VP *)R,*)D *)S *)B *)L *)P

*) = initial letters of two fiber types, e.g. GC (glass fiber + carbon fiber composite)

- 82 -

4. QUALITY OF FIBER AND BINDING MATERIAL 4.1 Fibers Fibers used in CFRMs shall satisfy the quality specifications given in Table 4.

Table 4: Specifications for fiber Fiber type Carbon fiber

Specification *)

Aramid fiber Glass fiber Vinylon fiber

Definition Carbon content not less than 92%, normally nongraphitic

*)

All aromatic series polyamide fiber

JIS R 3412, JIS R 3413 *)

Fibers satisfying the JIS standards, left Fibers of long chain synthetic polymers containing not less than 65% by weight of vinyl alcohol units(-CH 2-CHOH-)

*) = No Japanese or overseas standard available

4.2 Binding materials Binding materials used in CFRMs shall be either epoxy or vinyl ester types, satisfying the quality specifications given in Table 5.

Table 5: Specifications for binding materials Resin type

Specification

Epoxy

Conforming to standards for epoxide resins given in JIS K 7238

Vinyl ester

Conforming to standards for UP-CEE given in JIS K 6919

5. MECHANICAL PROPERTIES Required mechanical properties for CF RM are given in T able 6.

Table 6: Mechanical properties Identification symbol

Volume ratio Guaranteed of tensile axial fibers strength

Young's Elongation Modulus

2),4)

CR65,CD65 CR50A,CD50A CR50B,CD50B CS65A CS65B CL40

Vf

f 0

(%)

(N/mm )

(kN/mm )

63 - 66 49 49 - 52 64 - 66 64 - 66 43

1240 960* 780 980 790 1200*

99 – 170 200 190 73 – 210 84 – 170 100

2

E

2

- 83 -

ε0 (%)

Creep Relaxation Durability 3) failure rate 2) strength

f r

2

(N/mm ) 1.0 - 1.5 0.5 0.4 - 0.5 0.5 - 1.5 0.5 - 1.4 1.2

γ

(%) 2-3

1.04-1.06

C3D AR65,AD65 AS65A AS65B AB65 AP50 AL40 GR65,GD65 GL40 GCL40A GCL40B Remarks

60 65 60 - 69 60 - 69 66 49 43 65 - 68 40 40 40 Section 8.1

1490* 130 1720 59 – 60 1710 42 – 47 1830* 44 – 45 1400 63 – 78 1330 62 1300* 57 1130 37 - 49 590 30 530 37 530* 37 Section 8.6 Section 7.2

1.1 2.9 - 3.1 3.5 3.5 2.0 2.15 2.2 2.5 - 2.7 2.0 1.4 1.4 Section Section 8.8 7.3, 8.9

7 - 14 8.0 - 8.6 10 11 1.82

Section 7.4, 8.10

1) A or B following identification symbol refers to nominal diameter D: A : D ≤ 20 mm; B : D ≥ 20 mm 2) Strength, such as guaranteed tensile strength and creep failure strength, is obtained by dividing capacity, such as guaranteed capacity and creep failure capacity, by nominal cross sectional area 3) Not official values because test method was not identical 4) Data marked * refer not to average of many products but to average of one product 5) A blank cell indicates insufficient data available at present

6. NOMINAL DIAMETER AND MAXIMUM SIZE Nominal diameter and maximum size are tested according to sections 8.3 and 8.4; the maximum size ranges are given in table 7 and 8. Blank cells indicate data unavailable.

Table 7: Nominal diameters and maximum size ranges (1) Symbol CD(D) (20 types)

D

(mm) 3.0 5.0 9.0 10.0 12.0 8.0 10.0 12.0 5.0 7.9 9.8 12.0 5.0 7.9 9.8 12.0 12.5 20.0 25.0

Dmax

(mm)

9.0 - 9.4 10.2 - 10.6 12.5 - 12.8 9.0 - 9.4 10.9 - 11.3

14.0 - 16.0

- 84 -

Remarks (Designation) CFCC

Hiful CF (SNCP)

Hiful CF (ANCP)

Leadline PC-5 PC-D8 PC-D10 PC-D12 Leadline PC-R5 PC-R8 PC-R10 PC-R12 CFRP rod

CS (23 types)

CL (6 types)

C3D AR(D) (10 types)

AS (8 types)

AB (10 types)

30.0 5.0 7.5 10.5 12.5 15.2 17.8 25.0 40.0 12.5 15.0 21.0 25.0 30.0 35.0 15.0 25.0 30.0 12.5 15.0 21.0 25.0 30.0 35.0 4.7 7.1 9.1 11.3 13.7 15.8 10.0 3.0 4.0 6.0 7.4 8.0 3.0 4.0 6.0 8.0 7.5 12.4 12.7 15.2A 15.2B 17.8 19.3 20.3 21.8 7.3 9.0 10.4

CFCC

12.4 - 13.4 15.0 - 15.8

39.2 - 41.5 CFRP strand (standard)

CFRP strand (high strength) CFRP strand (high elasticity)

3.0 - 5.4 4.7 - 7.9 6.1 - 10.1 8.0 - 12.0 9.8 - 14.6 11.2 - 16.8 3.33 - 3.64 4.40 - 4.89 6.86 - 7.36 8.02 - 8.56 8.88 - 9.87 2.95 - 3.05 3.94 - 4.06 5.82 - 6.01 7.80 - 8.01 7.70 - 8.10 12.5 - 13.56 12.72 - 14.1 15.29 - 16.68 15.31 - 16.72 17.92 - 19.21 19.32 - 20.92 20.51 - 22.3 21.93 - 22.95 8.1 - 8.36 9.3 - 10.2 11.2 - 12.3 - 85 -

Nefmac C6 C10 C13 C16 C19 C22 BE3D Technora rod (deformed)

Technora rod (round)

Arapree Technora strand

FiBRA RA7 RA9 RA11

12.7 14.7 7.3 9.0 10.4 12.7 14.7 5.4 7.6 10.6 4.5 6.8 8.7 10.8 13.2

AP (3 types)

AL (5 types)

13.7 - 14.6 16.1 - 16.6 8.02 - 8.33 9.2 - 10.1 11.1 - 12.2 13.6 - 14.4 15.9 - 16.6

RA13 RA15 FiBRA FA7 FA9 FA11 FA13 FA15 Arapree

2.8 - 5.2 4.5 - 7.5 5.8 - 9.6 7.7 - 11.5 9.4 - 14.0

Nefmac A6 A10 A13 A16 A19

Table 8: Nominal diameters and maximum size ranges (2) Symbol

GR(D)

(6 types)

D

(mm)

Dmax

8.0

8.7 - 9.0

10.0

10.5 - 10.9

12.0

12.6 - 13.1

8.0

GL (8 types)

VR(D) (2 types)

(mm)

8.7 - 9.0

10.0

10.8 - 11.2

12.0

13.0 - 13.4

Remarks (Designation)

Hiful GF(SNGP)

Hiful GF(ANG)

2.4

1.1 - 2.9

3.3

2.0 - 3.8

G3

4.1

2.5 - 4.7

G4

6.7

4.1 - 7.7

G6

10.0

6.7 - 11.1

G10

12.9

8.6 - 14.4

G13

16.0

11.2 - 16.8

G16

19.4

13.8 - 20.6

G19

6.0

Nefmac G2

Claratec rod

10.0 GCL (6 types)

7.1

4.4 - 8.2

Nefmac H6

10.6

7.0 - 11.8

H10

13.7

9.2 - 15.2

H13

16.9

12.0 - 18.0

H16

20.7

15.2 - 21.4

H19

23.8

17.4 - 24.6

H22

7. TEST 7.1 Sampling

- 86 -

Test pieces shall be obtained as shown in Table 9.

Table 9: Sampling standards Nominal diameter Any nominal diameter

Sampling standard Sample taken from either end of a length or part of length* of CFRM

* Minimum unit : 100 m

7.2 Test for tensile strength (1) Test for tensile strength shall be conducted in accordance with JSCE-E 531 "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials" (2) Tensile strength shall be obtained by dividing the maximum resistant load by the nominal cross sectional area. (3) Young's modulus shall be obtained by dividing the tensile rigidity by the nominal cross sectional area.

7.3 Test for creep failure strength Test for creep failure strength shall be conducted in accordance with JSCE-E 533 "Test Method for Creep Failure of Continuous Fiber Reinforcing Materials".

7.4 Test for relaxation rate Test for relaxation rate shall be conducted in accordance with JSCE-E 534 "Test Long-Term Relaxation of Continuous Fiber Reinforcing Materials".

Method for

8. CALCULATION 8.1 Volume ratio of axial fiber The volume ratio of axial fiber refers to the ratio of the volume of axial fiber to the apparent volume of CFRM, and is obtained from the following equation:

VF = ( vfa / vt )

×

100

(%)

where

VF = volume ratio of axial fiber vfa = volume of axial fiber vt = apparent volume of CFRM 8.2 Nominal cross sectional area (1) Nominal cross sectional area refers to the value in mm2 obtained by dividing the volume of the CFRM by the length, following the method given in 8.2(2) below. The standard method for obtaining test pieces shall be as shown in Table 9, and the total number of test pieces shall be not less than 5. Where the cross section is uniform, as in rod type CFRMs, the nominal cross sectional area may be

- 87 -

calculated from the nominal diameter and π . (2) Calculation method of nominal cross sectional area 1) Measure the length L (mm) of one test piece (1 m approx.) accurately to the nearest 0.1 mm. 2) Fill a glass tube of cross sectional area Ag with water, and record the water level H 0 (mm). 3) Place the test piece gently in the glass tube, and record the water level H 1 (mm). 3

4) Calculate the volume of the test piece V (mm ) based on the difference between water levels H 0 and H1, and the cross sectional area of the glass tube. 5) Calculate the sectional area A according to the following equation 2

A = (H1 - H0) × Ag / L (mm ) 6) The average of the cross sectional areas A of not less than 5 test pieces shall be designated the nominal cross sectional area.

8.3 Nominal diameter "Nominal diameter" is the diameter applied to the CFRM, defined as the average value in mm of twice the square root of the result of dividing the nominal cross sectional area by π . For CFRMs with a rectangular section, the cross sectional area is calculated from the breadth and depth of test pieces, and the nominal diameter is defined as twice the square root of the result of dividing this cross sectional area by π . The method of obtaining test pieces, and the number of test pieces, shall be as for 8.2(2) Calculation method of nominal cross sectional area ".

8.4 Maximum size (1) "Maximum size" refers to the maximum dimension of the CFRM section, following the method given in 8.4(2) below. (2) Calculation method of maximum size 1) Obtain a test piece of length 1 m. 2) For test pieces of not less than 5, measure the maximum diameter in the two orthogonal directions to the nearest 0.1 mm, at both ends and in the center of the test piece. 3) The maximum diameter of not less than 5 test pieces shall be designated as the maximum size.

8.5 Nominal mass density (1) Nominal mass density (g/m) is obtained by dividing the mass of CFRM by the length, following the method given in 8.5(2) below. The standard method for obtaining test pieces shall be as shown in Table 9, and the total number of test pieces shall be not less than 5. (2) Calculation method of nominal mass density 1) Measure the mass of a test piece (length 1 m) to the nearest 0.1 g. 2) Measure the length of the test piece to the nearest 0.1 mm. 3) Calculate mass density by dividing the mass by the length. 4) The average of the mass densities of not less than 5 test pieces shall be designated the nominal mass density.

- 88 -

8.6 Guaranteed capacity (1) Guaranteed capacity is the characteristic value of the tensile capacity of CFRM, following the method given in 8.6(2) below. The standard method for obtaining test pieces shall be as shown in Table 9, and the total number of test pieces shall be not less than 20. (2) Calculation method of guaranteed capacity Guaranteed capacity shall be not more than the value which is obtained by subtracting three times the standard deviation from the average of the test results of not less than 20 test pieces conducted in accordance with JSCE-E 531 "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", and is rounded off to the nearest 100 N. Test pieces failing at the anchorage shall be disregarded.

8.7 Tensile rigidity (1) Tensile rigidity shall be calculated following the method given in 8.7(2) below. The standard method for obtaining test pieces shall be as shown in Table 9, and the total number of test pieces shall be not less than 20. The data for calculation of the tensile rigidity may be obtained during the test for the guaranteed capacity. (2) Calculation method of tensile rigidity Tensile rigidity shall be the average value of the results of not less than 20 test pieces, each result being calculated according to the following equation, using the values from the load - strain curve obtained in accordance with JSCE-E 531 "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials" at 20% and 60% of the guaranteed capacity. EA =

∆F

/∆ ε

where EA = tensile rigidity (kN) ∆ F = load increment from 20% to 60% of guaranteed capacity (kN) ∆ ε = strain increment from 20% to 60% of guaranteed capacity

8.8 Elongation (1) "Elongation" refers to the elongation corresponding to the guaranteed capacity, expressed as a percentage calculated following the method given in 8.8(2) below. The standard method for obtaining test pieces shall be as shown in Table 9, and the total number of test pieces shall be not less than 20. The data for calculation of elongation may be obtained during the tensile test for the guaranteed capacity. (2) Calculation method of elongation 1) Calculate elongation corresponding to the guaranteed capacity of each test piece, from the test results obtained in accordance with JSCE-E 531 "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", for not less than 20 test pieces. 2) Elongation shall be defined as the average elongation of not less than 20 test results.

- 89 -

8.9 Creep failure capacity "Creep failure capacity" is obtained by multiplying the creep failure capacity ratio at 1 million hours, which is obtained by extrapolation of the load ratio - failure time approximation curve in which data are shown up to 1000 hours obtained in accordance with JSCE-E 533 "Test Method for Creep Failure of Continuous Fiber Reinforcing Materials", by the guaranteed capacity.

8.10 Relaxation rate The relaxation rate is defined as the estimated relaxation after 1 million hours, which is obtained by extrapolation of the time - relaxation approximation curve in which data are shown up to 1000 hours obtained in accordance with JSCE-E 534 "Test Method for Long-Term Relaxation of Continuous Fiber Reinforcing Materials".

9. INSPECTION 9.1 Mechanical properties Mechanical properties shall be inspected following 7. TEST and 8 CALCULATION, confirming that the results conform to the mechanical properties listed in 5 MECHANICAL PROPERTIES.

9.2 Dimensions Dimensions shall be measured according to 8 CALCULATION, confirming that the results conform to the values given in 6. NOMINAL DIAMETER AND MAXIMUM SIZE.

- 90 -

TEST METHOD FOR TENSILE PROPERTIES OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 531-1995)

1. SCOPE This specifications specifies mainly the test method for tensile properties of CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specifications for Continuous Fiber Reinforcing Materials": (1) Test section: The part of a test piece subject to testing between the anchoring sections of the test piece (2) Anchoring section: The end part of a test piece where an anchorage is fitted to transmit loads from the testing machine to the test section (3) Gauge length: The distance between two gauge points on the test section providing a reference length for strain measurements (4) Anchorage : Device fitted to the anchoring section of a test piece to transmit loads from the testing machine to the test piece (5) Tensile capacity: The tensile load at the time of failure of the test piece (6) Guaranteed tensile capacity: Guaranteed value for the tensile capacity; if none is specified, the manufacturer's guaranteed tensile capacity shall be adopted (7) Ultimate strain : Strain corresponding to the tensile capacity

3. TEST PIECES 3.1 Preparation of test pieces Test pieces shall as a rule not be subjected to any processing. For mesh-type CFRM, linear test pieces may be prepared by cutting away extraneous parts in such a way as not to affect the performance of the part to be tested. However, processing will be permissible for anchoring sections to be provided in the test piece.

3.2 Handling of test pieces During the sampling and preparation of test pieces, all deformation, heating, outdoor exposure to ultraviolet light etc. causing changes to the material properties of the test section of the test piece must be avoided.

3.3 Length of test pieces The length of the test piece shall be the length of the test section added to the length of the anchoring

- 91 -

section. The length of the test section shall be not less than 100mm, and not less than 40 times the nominal diameter of the CFRM. For CFRM in strand form, as an additional condition, the length shall be more than 2 times the strand pitch.

3.4 Number of test pieces The number of test pieces shall not be less than five. If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

4. TESTING MACHINE AND DEVICES 4.1 Testing machine The testing machine to be used in tensile testing shall conform to JIS B 7721 (Tensile Testing Machines). The testing machine shall have a loading capacity in excess of the tensile capacity of the test piece, and shall be capable of applying loading at the required loading rate.

4.2 Anchorage The anchorage shall be suited to the geometry of the test piece, and shall have the capacity to transmit loads capable to cause the test piece to fail at the test section. The anchorage shall constructed so as to transmit loads reliably from the testing machine to the test section, transmitting axial loads only to the test piece, without transmitting either torsion or flexural force.

4.3 Extensometer and strain gauge The extensometer and strain gauge shall be capable of recording all variations in gauge length or -6 elongation during testing, with an accuracy of not less than 10×10 .

5. TEST TEMPERATURE The specifications test temperature shall generally be within the range 5~35°C. The test temperature for test pieces sensitive to temperature variations shall be 20±2°C.

6. TEST METHOD 6.1 Mounting of test piece When mounting the test piece on the testing machine, care must be taken to ensure that the longer axis of the test piece coincides with the imaginary line joining the two anchorages fitted to the testing machine.

6.2 Mounting of extensometer and strain gauge In order to determine the Young’s modulus and ultimate strain of the test piece, an extensometer or strain gauges shall be mounted in the center of the test section at a distance of at least 8 times the nominal diameter of the CFRM from the anchorages, correctly in the direction of tensioning. The gauge length when using an extensometer shall not be less than 8 times the nominal diameter of the CFRM. The gauge length for stranded CFRM shall not be less than 8 times the nominal diameter of the CFRM,

- 92 -

and not less than the length of the stranding pitch.

6.3 Loading rate 2

The specifications rate of loading the test piece shall be between 100~500 N/mm per minute. If a strain control type of testing machine is used, loading shall be applied to the test piece at a fixed strain rate 2 corresponding to 100~500 N/ mm per minute.

6.4 Scope of test The loading shall be completed until tensile failure, and the measurements shall be recorded until the strain reaches at least 60% of the tensile capacity or the guaranteed tensile capacity.

7. CALCULATION AND EXPRESSION OF TEST RESULTS 7.1 Handling of data The material properties of CFRM shall be assessed on the basis only of test pieces undergoing failure in the test section. In cases where tensile failure or slippage has clearly taken place at the anchoring section, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing in the test section is not less than five.

7.2 Load-displacement curve A load (stress) ~ displacement (strain) curve shall be derived from load or stress and strain measurements recorded.

7.3 Tensile strength Tensile strength shall be calculated according to Eq. (1), rounded off to three significant digits.

f u

Fu / A

=

(1)

where 2

f u = tensile strength (N/mm ) F u = tensile capacity (N) 2 A = nominal cross sectional area of a test piece (mm )

7.4 Tensile rigidity and Young’s modulus Tensile rigidity and Young’s modulus shall be calculated from the load difference between 20% and 60% of tensile capacity according to the load-strain curve obtained from extensometer or strain gauge readings according to Eq. (2) and (3), rounded off to three significant digits. For materials where a guaranteed tensile capacity is set, the values at 20% and 60% of the guaranteed tensile capacity may be used.

EA = E =

∆F / ∆ε ∆F

∆ε ⋅ A

(2) (3)

where

- 93 -

EA = tensile rigidity (N) 2 E = Young’s modulus(N/mm ) ∆ F = difference between loads at 20% and 60% of tensile failure capacity or guaranteed tensile

capacity ∆ε =

strain difference between the above two points

7.5 Ultimate strain Ultimate strain shall be the strain corresponding to the tensile failure capacity when strain gauge measurements of the test piece are available up to failure. If extensometer etc. measurements could not be made until failure, ultimate strain shall be calculated from the tensile capacity and Young’s modulus according to Eq. (4), rounded off to three significant digits.

εu =

F u EA

(4)

where εu =

ultimate strain

8. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, nominal cross sectional area (5) Date of test, test temperature, loading rate (6) Tensile capacity for each test piece, averages and specifications deviations for tensile capacity and tensile strength (7) Tensile rigidity and Young’s modulus for each test piece, and averages (8) Ultimate strain for each test piece, and averages (9) Stress-strain curve for each test piece

- 94 -

TEST METHOD

FOR

FLEXURAL

TENSILE

PROPERTIES

OF

CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 532-1995)

1. SCOPE This specifications specifies mainly the test method for flexural tensile properties of bent CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials", the "Quality Specifications for Continuous Fiber Reinforcing Materials" and the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials": (1) Deflected section: Section of a CFRM which is bent and maintained at the required bending angle and bending diameter ratio (2) Deflector: Device used to maintain the position, alter the bending angle, or alleviate the stress concentrations in the CFRM; sometimes installed in the deflected section (3) Bending angle : Angle formed by the straight sections of a test piece on either side of the deflector (4) Bending diameter ratio : Ratio of the external diameter of the deflector surface in contact with the CFRM, and the nominal diameter of the CFRM (5) Bending tensile capacity: Tensile load at the moment of failure of the test piece

3. TEST PIECES 3.1 Preparation and handling of test pieces Test pieces shall be prepared and handled in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

3.2 Length of test pieces The length of the test piece shall be the length of the test section added to the length of the anchoring section. The length of the test section shall not be less than 100mm from the anchorages to the deflected section, and not less than 40 times the nominal diameter of the CFRM. For CFRM in strand form, as an additional condition, the length shall be not less than 2 times the strand pitch.

3.3 Number of test pieces The number of test pieces shall not be less than three for each test condition (combination of bending diameters and bending angles). If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

- 95 -

4. TESTING MACHINE AND DEVICES 4.1 Testing machine The testing machine must include a loading device, load indicator, anchorages holder and deflector. The testing machine must also have a structure capable of continuing the test up to the tensile failure.

4.2 Loading device The loading device shall have a loading capacity in excess of the tensile capacity of the test piece, and shall be capable of applying loading at the required loading rate.

4.3 Load indicator The load indicator must be capable of displaying loads with an accuracy of not less than 1% of the failure load, up to failure of the test piece.

4.4 Anchorage holder The anchorage holder must be suited to the geometry of the test piece, and must be capable of acc urately transmitting loads from the testing machine to the test piece. It must be structured so as to transmit axial loads only to the test piece, without transmitting either torsion or flexural force.

4.5 Deflector The deflector must be capable of maintaining the required bending angle and bending diameter during the test until failure of the test piece. The surface of the defle ctor in contact with the test piece must be robust and smooth.

5. TEST TEMPERATURE The specifications test temperature shall generally be within the range 5~35°C. The test temperature for test pieces sensitive to temperature variations shall be 20±2°C.

6. TEST METHOD 6.1 Test preparation The bending diameter and bending angle shall be set appropriately for the test. This combination then forms a single test condition. As a specifications configuration, only one deflected s ection shall be set up in the test piece.

6.2 Mounting of test piece Care shall be taken when mounting the test piece on the testing machine to maintain the required bending angle and bending diameter at the deflected section during the test.

6.3 Loading rate 2

The specifications rate of loading the test piece shall be between 100~500 N/mm per minute.

6.4 Scope of test - 96 -

Loading shall be applied until failure of the test piece. Load and failure location shall be measured and recorded at the time of failure.

7. CALCULATION AND EXPRESSION OF TEST RESULTS 7.1 Handling of data The material properties of CFRM shall be assessed on the basis only of test pieces undergoing failure in the test section. In cases where tensile failure or slippage has clearly taken place at the anchoring section, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing in the test section is not less than three.

7.2 Bending tensile capacity The average, maximum, minimum, and specifications deviation of the bending tensile capacity for each set of test conditions shall be calculated.

7.3 Failure patterns The location and mode of failure shall be observed and recorded for each test piece.

8. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of test, test temperature, loading rate (6) Condition of surface of CFRM (material, thickness, configuration etc. of any coating, etc.) (7) Bending angle, external diameter of surface position of deflected section, bending diameter ratio, material and surface configuration (8) Bending tensile capacity for each test piece (9) Location and mode of failure for each test piece (10) Numbers of test pieces for each set of conditions in (7); average, maximum, minimum, and specifications deviation of the bending tensile capacity

- 97 -

TEST METHOD FOR CREEP FAILURE OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 533-1995)

1. SCOPE This specifications specifies mainly the test method for creep failure of CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specifications for Continuous Fiber Reinforcing Materials": (1) Creep: Time-dependent deformation when CFRM is subjected to a sustained constant load at a constant temperature (2) Creep strain: Strain occurring in a test piece due to creep (3) Creep failure : Failure occurring in a test piece due a sustained load (4) Creep failure time : Time between start of a sustained load, and failure of the test piece (5) Creep failure capacity: Load causing failure after a specified period of time from the start of a sustained load. In particular, the load causing failure after 1 million hours is referred to as the million hour creep failure capacity. (6) Creep failure strength: Stress causing failure after a specified period of time from the start of a sustained load. In particular, the stress causing failure after 1 million hours is referred to as the million

hour creep failure strength. (7) Load ratio : Ratio of a constant sustained load applied to a test piece, and the tensile failure load

3. TEST PIECES 3.1 Preparation, handling and dimensions of test pieces Test pieces shall be prepared and handled in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

3.2 Number of test pieces The number of test pieces for each test condition shall not be less than three. If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

4. TESTING MACHINE AND DEVICES 4.1 Testing machine - 98 -

The testing machine must be capable of maintaining constant, sustained loading even during deformation of the test piece.

4.2 Anchorage The anchorage must be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

4.3 Extensometer and strain gauge The extensometer and strain gauge must be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

4.4 Hour meter The hour meter for measuring the passage of time must be accurate to within 1% of the elapsed time .

5. TEST TEMPERATURE The test temperature shall normally be within the range 20±2°C, except in special circumstances.

6. TENSILE CAPACITY The tensile capacity shall be calcula ted in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

7. TEST METHOD 7.1 Mounting of test piece, and gauge distance Mounting of test pieces and gauge length shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

7.2 Loading (1) Care must be taken during loading to prevent the test piece from being subjected to any shock or vibration. (2) Creep test measurement is considered to start at the moment when of the prescribed load to the test piece has been completed.

7.3 Selection of sustained loads to be applied (1) Creep tests must be conducted for not less than five sets of load ratio conditions, selected on the basis of the tensile capacity. (2) One set of load ratio conditions must be such that three test pieces must not fail after 1000 hours of loading.

7.4 Measurement of creep strain Creep strain shall be recorded automatically by a recorder attached to the testing machine. If no recorder

- 99 -

is attached to the testing machine, creep strain shall be measured and recorded after the following times have elapsed: 1, 3, 6, 9, 15, 30, 45 minutes; 1, 1.5, 2, 4, 10, 24, 48, 72, 96, 120 hours; and in general every 24 hours subsequently, with a minimum of one measurement in every 120 hours.

8. CALCULATION AND EXPRESSION OF TEST RESULTS 8.1 Handling of data The material properties of CFRM shall be assessed on the basis only of test pieces undergoing failure in the test section. In cases where tensile failure or slippage has clearly taken place at the anchoring section, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing in the test section is not less than three. Data for test pieces breaking at the start of loading shall be disregarded. In such cases, the applied load and the creep failure time only shall be recorded but excluded from the data, although no additional tests need be performed.

8.2 Load ratio - creep failure time curve For each test piece subjected to creep test, the load ratio - creep failure time curve shall be plotted on a semi-logarithmic graph where the load ratio is represented on an arithmetic scale on the vertical axis, and creep failure time in hours is represented on an logarithmic scale on the horizontal axis.

8.3 Creep failure line chart A creep failure line chart shall be prepared, calculating an approximation line fr om the graph data by the least-squares method according to Eq. (1).

Y

=

a − b log T (1)

where Y = load ratio a,b = empirical constants T = time (h)

8.4 Creep failure capacity and creep failure strength The load ratio at 1 million hours (approximately 114 years) determined from the calculated approximation line shall be the creep failure load ratio; the load and stress corresponding to this creep failure load ratio shall be the million hour creep failure capacity and the million hour creep failure strength respectively. The million hour creep failure strength shall be calculated according to Eq. (2), rounded off to three significant figures

f r

=

Fr / A

(2)

where

- 100 -

2

f r = million hour creep failure strength (N/ mm ) F r = million hour creep failure capacity (N) 2 A = nominal cross sectional area of test piece (mm )

9. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of test, test temperature (6) Type and name of test machine (7) Type and name of anchorage (8) Tensile capacity, and average tensile capacity and tensile strength for each test piece (9) Load ratios and creep failure time curve for each test piece (10) Formula for derivation of approximation line (11) Creep failure load ratio, million hour creep failure capacity and million hour creep failure strength

- 101 -

TEST METHOD FOR LONG-TERM RELAXATION OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 534-1995)

1. SCOPE This specifications specifies mainly the test method for evaluating the relaxation ratio for long-term relaxation under a given constant temperature and strain, for CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specific ations for Continuous Fiber Reinforcing Materials": (1) Relaxation: Refers to stress relaxation: the time-dependent decrease in load in a CFRM held at a given constant temperature with a prescribed initial load applied and held at a given constant strain . (2) Relaxation rate : Percentage reduction of loading relative to the initial load after a given period of time when an initial load is applied and the strain fixed. In particular, the relaxation value after 1 million hours (approximately 114 years) is referred to as the million year relaxation rate. (3) Tensile capacity: The average of the tensile failure loads determined based on tests conducted in according with the "Test Method for Tensile Testing of Continuous Fiber Reinforcing Materials". The test temperature shall normally be within the range 20±2°C, except in special circumstances.

3. TEST PIECES 3.1 Preparation, handling and dimensions of test pieces Test pieces shall be prepared and handled in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

3.2 Number of test pieces The number of test pieces for each test condition shall not be less than three. If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

4. TESTING MACHINE AND DEVICES 4.1 Testing machine The testing machine must be capable of applying a sustained load while maintaining a constant length. 2 The machine must be capable of loading at a rate of 200±50 N/mm per minute.

- 102 -

4.2 Anchorage The anchorage must be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

4.3 Accuracy of initial load The accuracy of the initial load applied to the test piece shall be as follows: Test machines with loading capacity of equal to or less than 1 kN: ±1.0% of set load Test machines with loading capacity of more than 1 kN: ±2.0% of set load

4.4 Accuracy of load measurements The accuracy of readings or automatic recording of loads applied to the test piece shall be within 0.1% of the initial load.

4.5 Strain fluctuations -6

The test machine shall control strain fluctuations no greater than ±25×10 in the test piece throughout the test period, once the strain in the test piece has been fixed. If the CFRM slips from the anchoring section, the distance of slippage shall be compensated so as not to affect the test results.

4.6 Extensometer and strain gauge If an extensometer or strain gauge is to be fitted to the test piece, the extensometer or strain gauge shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

4.7 Hour meter The hour meter for measuring the passage of time must be accurate to within 1% of the elapsed time.

5. TEST TEMPERATURE The test temperature shall normally be within the range 20±2°C, except in special circumstances. Where the test results are heavily dependent on temperature, additional tests shall be performed at 0°C and at 60°C. In either case, temperature fluctuation over the test period shall be not more than ±2°C.

6. TEST METHOD 6.1 Mounting of test piece and gauge length Mounting of test pieces and gauge length shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

6.2 Prestretching If a strain gauge is to be set to the test piece, the test piece shall first be stretched taut by applying a load of 10~40% of the prescribed initial load, thereafter the strain gauge shall be attached and correctly calibrated.

6.3 Initial load - 103 -

The initial load shall be either 70% of the guaranteed tensile capacity, or 80% of the million hour creep failure capacity, whichever is the smaller.

6.4 Application of initial load (1) The initial load must be applied without subjecting the test piece to any shock or vibration. 2 (2) The specifications rate of loading the test piece shall be between 200±50 N/ mm per minute. (3) The strain on the test piece shall be fixed after the initial load has been applied to the test piece, and maintained for 120±2 seconds. This time shall be deemed to be the test start time.

6.5 Measurement of load reduction Load reduction shall generally be measured over a period of at least 1000 hours. Load reduction shall be recorded automatically by a recorder attached to the testing machine. If no recorder is attached to the testing machine, load reduction shall be measured and recorded after the following times have elapsed: 1, 3, 6, 9, 15, 30, 45 minutes; 1, 1.5, 2, 4, 10, 24, 48, 72, 96, 120 hours; and in general every 24 hours subsequently, at a minimum of one measurement every 120 hours.

7. CALCULATION AND EXPRESSION OF TEST RESULTS 7.1 Relaxation value The relaxation value shall be calculated by dividing the load measured in the relaxation test by the initial load.

7.2 Relaxation curve The relaxation curve shall be plotted on a semi-logarithmic graph where the relaxation value (%) is represented on an arithmetic scale on the vertical axis, and test time in hours is represented on an logarithmic scale on the horizontal axis. An approximation line for Eq. (1) shall be derived from the graph data using the least-square method.

Y

=

a − b log T

where Y = relaxation rate (%) a,b = empirical constants T = time (h)

7.4 Million hour relaxation rate The relaxation rate after 1 million hours (approximately 114 years) shall be evaluated from the approximation line; this value represents the million hour relaxation rate. Where the service life of the structure in which the CFRM is to be used is determined in advance, the relaxation rate for the number of years of service life ("service life relaxation rate") shall also be determined.

8. TEST REPORT The test report shall include the following items: (1) Name of CFRM

- 104 -

(2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, nominal cross sectional area (5) Date of test, test temperature and temperature fluctuations (6) Type of test machine (7) Initial load and loading rate of initial load (8) Guaranteed tensile capacity, and ratio of initial load to guaranteed tensile capacity (9) Relaxation curve for each test piece (10) Average relaxation rates at 10, 120 and 1000 hours (11) Formula for derivation of an approximation line (12) Million hour relaxation rate (13) Relaxation rate corresponding to design service life allowed for in design ("service life relaxation rate"), where applicable

- 105 -

TEST METHOD FOR TENSILE FATIGUE OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 535-1995)

1. SCOPE This specifications specifies mainly the test method for tensile fatigue under constant tensile loading for CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials", the "Quality Specifications for Continuous Fiber Reinforcing Materials", and the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials": (1) Repeated load (stress): Load (stress) alternating simply and cyclically between fixed maximum and minimum values (2) Maximum repeated load (stress): Maximum load (stress) during repeated loading (stressing) (3) Minimum repeated load (stress): Minimum load (stress) during repeated loading (stressing) (4) Load (stress) range : Difference between maximum and minimum repeated load (stress) (5) Load (stress) amplitude : One-half of the load (stress) range (6) Average load (stress): Average of the maximum and minimum repeated load (stress) (7) Number of cycles : Number of times the repeated load (stress) is applied to the test piece (8) S-N curve : Curve plotted in a graph with repeated stress on the vertical axis and the number of cycles to fatigue failure on the horizontal axis (9) Fatigue strength : Maximum repeated stress at which the test piece does not fail at the prescribed number of cycles (10) Frequency: Number of loading (stressing) cycles in one second during the test

3. TEST PIECES 3.1 Preparation, handling and dimensions of test pieces Preparation, handling and dimensions of test pieces shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

3.2 Number of test pieces The number of test pieces should be at least three, for each of at least three levels of loading (stress). If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

4. TESTING MACHINE AND DEVICES - 106 -

4.1 Testing machine The testing machine shall be capable of maintaining a constant load (stress) amplitude, maximum and minimum repeated load (stress), and frequency. The testing machine shall be fitted with a counter capable of recording the number of cycles to failure of the test piece. The accuracy of the load shall be within 1% of the load range.

4.2 Anchorage The anchorage must be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". Ideally the same type of anchorage should be used for all in a given series of tests.

4.3 Strain measurements If strain measurements are required as part of the fatigue tests, an extensometer and strain gauge capable of maintaining an accuracy of ±1% of the indicated value during the test shall be used.

5. TEST TEMPERATURE The test temperature shall generally be within the range 5~35°C. The specifications test temperature for test pieces sensitive to temperature variations shall be 20±2°C.

6. TEST METHOD 6.1 Mounting of test pieces Mounting of test pieces shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

6.2 Load setting Load may be set in two ways: either fixing the average load and varying the load amplitude, or fixing the minimum repeated load by partial pulsation and varying the maximum repeated load. The method adopted shall be determined according to the purpose of the test. In either case, at least three load levels 3

6

shall be set within the range of number of cycles to failure 10 to 2×10 .

6.3 Frequency The frequency shall normally be within the range 1~10 Hz.

6.4 Start of test After static loading up to the average load, repeated loading shall be commenced. The prescribed load shall be introduced rapidly and without any shock. The maximum and minimum repeated loads shall remain constant for the duration of the test. Counting of the number of cycles shall normally commence when the load on the test piece has reached the prescribed load.

6.5 End of test - 107 -

Complete separation (breaking) of the test piece shall be deemed to constitute failure, and the number of 6 cycles to failure shall be recorded. If the test piece doesn’t fail after 2×10 cycles, the test may be discontinued. Test pieces that did not fail must not be reused.

6.6 Interruption of test Tests shall normally be conducted without interruption for each test piece from the start of the test to the end of the test. When a test is interrupted, the number of cycles up to the time of interruption, and the period of the interruption shall be recorded.

7. CALCULATION AND EXPRESSION OF TEST RESULTS 7.1 Handing of data Data for test pieces that slipped from the anchoring section shall be disregarded in assessing the material properties of the CFRM. In cases where tensile failure or slippage has clearly taken place at the anchoring section, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing in the test section is not less than three.

7.2 S -N curve The S-N curve shall be plotted with the maximum repeated stress, stress range or stress amplitude represented on an arithmetic scale on the vertical axis, and the number of cycles represented on a logarithmic scale on the horizontal axis. Where measurement points coincide, the number of coinciding points shall be noted. Right-facing arrows shall be added to indicate points representing test results for test pieces remaining that did not fail.

7.3 Fatigue strength 6

The fatigue strength after 2×10 cycles shall be derived from the S-N curve. The fatigue strength shall be rounded off to three significant digits.

8. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of test, test temperature and humidity (from start to end of test) (6) Maximum load (stress), minimum load (stress), load (stress range), number of cycles to failure, and frequency rate for each test piece (7) Record of observed failure mode for each test piece (8) S-N curve

- 108 -

TEST METHOD FOR COEFFICIENT OF THERMAL EXPANSION OF CONTINUOUS

FIBER

REINFORCING

MATERIALS

BY

THERMO-MECHANICAL ANALYSIS (JSCE-E 536-1995)

1. SCOPE This specifications specifies mainly the test method for measuring the coefficient of thermal expansion of CFRM used in place of steel reinforcement or prestressing tendon in concrete by thermomechanical analysis.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specifications for Continuous Fiber Reinforcing Materials": (1) Thermomechanical analysis (TMA): Method for measuring deformation of a material as a function of either temperature or time, by varying the temperature of the material according to a calibrated program, under a non-vibrating load (2) TMA curve : In the context of TMA, a graph with temperature or time represented on the horizontal axis, and deformation on the vertical axis (3) Coefficient of thermal expansion : the average coefficient of linear thermal expansion between given temperatures. The average of the given temperatures is taken as the representative temperature.

3. TEST PIECES 3.1 Pre-test curing of test pieces Prior to testing, test pieces shall normally be kept for a minimum of 24 hours at a temperature of 20±2°C and relative humidity of 65±5%, under Specifications Temperature Conditions Class II and Specifications Humidity Conditions Class II, in accordance with JIS K 7100. The test pieces shall then normally be kept for 48 hours at the maximum test temperature, in order to eliminate strain resulting from bending, and for dehumidification and deaeration.

3.2 Dimensions of test piece The specifications test piece cut from the CFRM shall be 20mm in length, with a round or square cross-section of diameter or breadth of not more than 5mm.

3.3 Number of test pieces The number of test pieces shall be not less than three.

- 109 -

4. TESTING DEVICE 4.1 Testing device The TMA apparatus used for testing shall be capable of measuring in compression mode, of maintaining a constant atmosphere around the test piece, and of raising the temperature of the test piece at a constant rate.

4.2 Calibration of testing device (1) Sensitivity calibration of the displacement gauge shall be carried out periodically using either an external micrometer as defined in JIS B 7502, or a micrometer attached to the testing machine. (2) Calibration of the temperature gauge shall be carried out using a pure substance of known melting point.

4.3 Installation of testing device The TMA apparatus must be installed in a location not subject to vibration during testing.

5. TEST METHOD 5.1 Mounting of test piece The test piece, gauge rod and test platform shall be cleaned, and the test piece placed upright and if possible bonded to the platform. 5.2 The gauge rod shall be placed in the center of the test piece, with no pressure applied. 5.3 The atmosphere around the test piece shall consist of dry air (water content not more than 0.1% w/w) or nitrogen (water content not more than 0.001% w/w, oxygen content not more than 0.001% w/w), maintained at a flow rate in the range of 50~100 ml /min. 5.4 The load shall be applied gently to the tip of the gauge rod at room temperature, and in general the temperature shall first be lowered to 0°C then raised to 60°C, and the full process of displacement of the test piece shall be recorded. 5.5 The rate of temperature increase shall not be more than 5°C per minute. 2

5.6 The compressive stress acting on the test piece shall be around 4 mN/ mm .

6. CALCULATION AND EXPRESSION OF TEST RESULTS 6.1 The coefficient of thermal expansion of the test piece within the measured temperature range ( T 1~ T 2 ) shall be calculated according to Eq. (1). α sp = ( ∆ Lspm − ∆Lrefm )

/ {L0 × (T2 − T 1 )} + α set

- 110 -

(1)

where a sp = coefficient of thermal expansion (/°C) ∆ L spm =

difference in length of test piece between temperatures T 1 and T 2 (µm) ∆ Lrefm = difference in length of specifications test piece for length calibration between temperatures T 1 and T 2 (µm) L0 = length of test piece at room temperature (µm) T 2 = maximum temperature for calculation of coefficient of thermal expansion (normally 60°C) T 1 = minimum temperature for calculation of coefficient of thermal expansion (normally 0°C) a set = coefficient of thermal expansion calculated for specifications test piece for length calibration between temperatures T 1 and T 2 (/°C) For apparatus in which the test piece and specifications test piece for length calibration are measured simultaneously, ∆ Lrefm shall be = 0 in the above equation.

6.2 Rounding off of numerical values -7 Each of the coefficients of thermal expansion shall be calculated to six decimal places (10 ), and the -6 average value rounded off to five decimal places (10 ). If the average value is less than 1, it shall be -7 expressed accurate to six decimal places (10 ).

7. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, nominal cross sectional area (5) Date of test (6) Dimensions of test pieces (7) Pre-test curing method (8) Type of testing machine (9) Type of ambient atmosphere during test, and flow rate (10) Name of substance used for temperature calibration, and measurements taken (11) Type of specifications test piece for length calibration (12) Temperature range for which the coefficient of thermal expansion was measured, and representative temperature (13) TMA curve for each test piece (14) Coefficient of thermal expansion for each test piece, and average coefficient of thermal expansion

- 111 -

TEST METHOD FOR PERFORMANCE OF ANCHORAGES AND COUPLERS IN PRESTRESSED CONCRETE USING CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 537-1995)

1. SCOPE This specifications specifies mainly the test method for performance of anchorages and couplers used with CFRM used in place of steel reinforcement or prestressing tendon in concrete.

2. DEFINITIONS The following terms are defined for general use in this Specifications, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specifications for Continuous Fiber Reinforcing Materials": (1) CFRM tendon: CFRM used as tendons in prestressed concrete (2) Anchorage : Device anchoring a CFRM tendon to the concrete, transmitting prestressing force to the members (3) Anchorage reinforcement: Latticed or spiral reinforcing steel or CFRM connected with the anchorage and arranged behind it (4) Anchoring section: The section around the anchorage and the anchorage reinforcement, including the surrounding concrete (5) Coupler: Device coupling tendons

3. TEST METHOD FOR PERFORMANCE OF ANCHORAGES 3.1 Purpose of test To determine the tensile capacity when anchorage are used in conjunction with CFRM tendons

3.2 Test pieces 3.2.1 Preparation of test pieces Test pieces shall be prepared by attaching an anchorage to one or both ends of a CFRM tendon.

3.2.2 Dimensions of test piece The specifications length of test pieces shall be 3 meters.

3.2.3 Number of test pieces The number of test pieces shall be no less than three.

3.3 Test temperature

- 112 -

The test temperature shall generally be within the range 5~35°C. Testing of test pieces which are sensitive to temperature or are to be used at high temperatures shall if necessary be tested at the service temperature.

3.4 Test method 3.4.1 Mounting of test piece Test pieces shall be mounted supported by a tensile loading testing machine. The area and geometry of the surface supporting the anchorage, the tension in the CFRM tendons, and the manner of application of forces shall approximate the actual conditions within the prestressed concrete structure as close as possible.

3.4.2 Loading rate 2

CFRM tendons shall in general be loaded at a rate of 100~500 N/ mm .

3.4.3 Scope of test Loading shall be continued up to the tensile failure , as determined by either failure of the CFRM t endon or excessive deformation of the anchoring device.

3.5 Calculation and Expression of test results The tensile capacity for each test piece and the average tensile capacity shall be calculated. Modes of failure shall also be recorded. In the expression of the loading test, any deformation, damage, caving in etc. of the anchorage shall be recorded.

4. TEST METHOD FOR PERFORMANCE OF COUPLERS 4.1 Purpose of test To determine the tensile capacity when couplers are used in conjunction with CFRM or other tendons

4.2 Test pieces 4.2.1 Preparation of test pieces Test pieces shall be prepared by attaching CFRM or other tendons to either end or both ends of a coupler. Any other tendons and their couplers must have adequate strength as compared to the CFRM tendons being tested.

4.2.2 Dimensions of test piece The specifications length of test pieces shall be 3 meters.

4.2.3 Number of test pieces The number of test pieces shall be no less than three.

4.3 Test temperature The test temperature shall generally be within the range 5~35°C. Testing of test pieces which are sensitive to temperature or are to be used at high temperatures shall if necessary be tested at the service

- 113 -

temperature.

4.4 Test method In accordance with 3.4, Test method for performance of anchorages

4.5 Calculation and expression of test results The tensile capacity for each test piece and the average tensile capacity shall be calculated. Modes of failure shall also be recorded. In the expression of the loading test, any deformation, damage, caving in etc. of the couplers shall be recorded.

5. TEST METHOD FOR PERFORMANCE OF ANCHORING SECTIONS 5.1 Purpose of test To determine the performance of the anchoring section, including the concrete in the vicinity of the anchorage and the anchorage reinforcement.

5.2 Test pieces 5.2.1 Preparation and dimensions of test pieces The distance from the center of the anchorage to the edge of the concrete shall be the minimum allowable distance determined according to the design. The length of one side of the cross section of a concrete test piece shall be 2 times the minimum allowable distance, and the height of the section below the anchorage shall not be less than 2 times the length of the longer side.

5.2.2 Reinforcement of concrete The section around the anchorage shall be uniformly reinforced using the anchorage reinforcement and additional bars prescribed for the anchorage. Sections other than that around the anchorage shall be reinforced with additional bars to prevent failure during the test. The material quality of the anchorage reinforcement and additional bars shall be determined according to the purpose of reinforcement.

5.2.3 Concrete quality The concrete shall be made with normal aggregates, with coarse aggregates having a maximum dimension of 20 or 25 mm. The specifications concrete shall have a slump of 10±2 cm, and the 2

compressive strength at 28 days shall be 30±3 N/ mm .

5.3 Test method 5.3.1 Loading test Loading shall be continued up to the failure. The specifications loading method shall be application of compressive force to the anchorage, but methods applying tension to combinations of tendons may also be adopted.

5.3.2 Timing of test Tests shall normally be performed when the compressive strength of the concrete has reached 24±3 N/ 2

mm .

- 114 -

5.4 Calculation and Expression of test results In the expression of the loading test, any deformation, damage, caving in etc. of the anchorage shall be recorded.

6. TEST REPORT The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of test, test temperature, loading rate (6) Dimensions of test pieces (7) Concrete mix, slump, and compressive strength at time of testing (8) (For anchorage and coupler performance tests:) tensile failure capacity for each test piece, average tensile failure capacity, and failure modes (9) (For anchoring section performance test:) failure capacity (10) Records of any deformation, damage, caving in etc. of anchorages, couplers, anchoring sections

- 115 -

TEST METHOD FOR ALKALI RESISTANCE OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 538-1995)

1. SCOPE This specif ications specifies mainly the test method for evaluating alkali resistance of CFRM used in place of steel reinforcement or prestressing tendon in concrete by immersion in an aqueous alkaline solution.

2. TEST PIECES 2.1 Preparation of test pieces Test pieces shall as a rule not be subjected to any processing. For mesh-type CFRM, linear test pieces may be prepared by cutting away extraneous parts in such a way as not to affect the performance of the part to be tested.

2.2 Handling of test pieces During sampling and preparation of test pieces, all deformation, heating, outdoor exposure to ultraviolet light etc. causing changes to the material properties of the test section of the test piece must be avoided.

2.3 Length of test pieces The length of the test section shall not be less than 100mm, and not less than 40 times the nominal diameter of the CFRM. For CFRM in strand form, as an additional condition, the length shall not be less than 2 times the strand pitch.

2.4 Number of test pieces The number of test pieces for pre- and post-immersion tensile testing shall not be less than five. If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

3. IMMERSION IN ALKALINE SOLUTION 3.1 Preparation of alkaline solution The alkaline solution used for immersion shall have the same composition as the pore solution found in the concrete.

3.2 Prevention of infiltration of solution into test piece In order to prevent infiltration of the solution via the ends of the test pieces during immersion, both ends of the test pieces shall be covered with epoxy resin.

3.3 Immersion temperature The specifications temperature for immersion shall be 60°C.

- 116 -

3.4 Mounting of test piece The test piece shall be mounted on the immersion apparatus. If necessary a tensioning load shall be applied to the test piece. The alkaline solution must be prevented from absorbing CO 2 from the air and from the evaporation of water during immersion.

3.5 Period of immersion The specifications immersion period shall be one month.

3.6 Post-immersion treatment The test piece shall be washed in water after immersion.

4. EXTERNAL APPEARANCE AND MASS CHANGE 4.1 Inspection of alkaline solution The pH value of the alkaline solution shall be measured before and after the alkali resistance test.

4.2 External appearance The external appearance of the test piece shall be examined before and after the alkali resistance test, for comparison of color, surface condition, and change of shape. If necessary the test piece may be sectioned and polished, and the condition of the cross-section examined using a microscope, etc.

4.3 Measurement of mass change After immersion, the hardened epoxy resin shall be removed from the ends of the test piece, which shall then be dried and the mass measured until the mass is constant. The rate of mass loss shall be calculated according to Eq. (1). Rate of mass loss (%) = {(W 0/ L0 - W 1/ L1)/(W 0 / L0)}×100 (1) where W 0 = mass before immersion (g) L0 = length before immersion (mm) W 1 = mass after immersion (g) L1 = length after immersion (mm)

5. TENSILE TEST 5.1 Testing machine and devices Testing machine and devices shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

5.2 Test temperature and test method Test temperature and test method shall be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

- 117 -

6. CALCULATION AND EXPRESSION OF TEST RESULTS 6.1 Handling of data The material properties of CFRM shall be assessed on the basis only of test pieces undergoing failure in the test section. In cases where tensile failure or slippage has clearly taken place at the anchoring section, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing in the test section is not less than five.

6.2 Tensile capacity retention rate The tensile capacity retention rate shall be calculated according to Eq. (2), and rounded off to 2 significant places.

Re t

=

( Fu1 / F u 0 ) × 100

(2)

where Ret = tensile capacity retention rate (%) F u 1 = tensile capacity before immersion (N) F u 0 = tensile capacity after immersion (N)

7. TEST REPORT The test report shall include the following items:

7.1 Common items (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of start and end of immersion

7.2 Items related to alkaline solution immersion (1) Composition of alkaline solution, pH, temperature, immersion period and time (2) Tensioning load and ratio of tensioning load to nominal tensile capacity (if tensioning is not carried out, this fact should be noted) (3) Record of observation of external appearance, and rate of mass loss

7.3 Items related to tensile testing (1) Test temperature and loading rate (2) Tensile capacities for immersed and non-immersed test pieces, with averages and specifications deviations of tensile capacities and tensile strength (3) Tensile rigidity, Young’s modulus and the averages of these for all immersed and non-immersed test pieces

- 118 -

(4) Ultimate strain for all immersed and non-immersed test pieces, and average ultimate strain (5) Tensile capacity retention rate (6) Stress-strain curve for all immersed and non-immersed test pieces

- 119 -

TEST METHOD FOR BOND STRENGTH OF CONTINUOUS FIBER REINFORCING MATERIALS BY PULL-OUT TESTING (JSCE-E 539-1995)

1. SCOPE This standard specifies mainly the test method of determining the bond strength of CFRM used in place of steel reinforcement or prestressing tendon in concrete by pull-out testing.

2. DEFINITIONS The following terms are defined for general use in this Standard, in addition to the terms used in the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Specifications for Continuous Fiber Reinforcing Materials": Nominal peripheral length: The peripheral length of the CFRM which forms the basis for calculation of bond strength; determined separately for each CFRM

3. TEST PIECES 3.1 Fabrication of test pieces Test pieces shall normally be cube-shaped, fabricated by pouring concrete around a central CFRM. The bonded length of the CFRM shall be a typical section of the surface of the CFRM set up in the free end side. The length shall normally be 4 times the diameter of the CFRM. If the bonded length as defined above is thought not to represent the bonding characteristics of the CFRM, the bonded length may be extended as appropriate. In order to equalize the stress from the loading plate on the loaded end side, sections other than the bonded section shall be sheathed with PVC etc. to prevent bonding.

3.2 Dimensions of test piece The dimensions of the test piece shall be determined according to the dimensions of the CFRM, as shown in table 1:

Table 1: Dimensions of test pieces CFRM nominal diameter

Length of one face of test piece (cm)

Bonded length

External diameter of spiral hoop reinforcement (cm)

Less than 17 mm 17 ~ 30 mm

10×10×10 15×15×15

4×nominal diameter 4×nominal diameter

8 ~ 10 12 ~ 15

- 120 -

3.3 Dimensions of CFRM tendon The CFRM tendon shall be allowed to protrude by around 10 mm at the free end side, and the end face must be structured so as to allow access for a dial gauge etc., used to measure the length of pull-out. The loading end side of the CFRM tendon must be long enough to allow the performance of the pull-out test, and must be fitted with an anchoring section, gripping device or similar apparatus to allow transmission of loads.

3.4 Arrangement of CFRM tendons CFRM tendons shall be arranged horizontally in the center of the test piece.

3.5 Reinforcement of test pieces Test pieces shall be reinforced with spiral hoops centered at the test piece to prevent splitting failure while the test is in progress. Spiral reinforcement hoops shall be 6 mm in diameter, with a spiral pitch of 4 cm. The ends of the spiral hoops shall be welded, or 1.5 times extra turns shall be provided.

3.6 Number of test pieces The number of test pieces shall not be less than three. If the test piece is found clearly to have failed at the anchoring section, or to have slipped out of the anchoring section, an additional test shall be performed on a separate test piece taken from the same lot.

4. FORMS Forms shall conform to the JSCE "Test method for bond strength of concrete by pull-out testing" (JSCE-G 503-1988).

5. CONCRETE QUALITY The concrete shall be made with normal aggregates, with coarse aggregates having a maximum dimension of 20 or 25 mm. The standard concrete shall have slump of 10±2 cm, and the compressive 2

strength at 28 days shall be 30±3 N/mm .

6. PLACING OF CONCRETE 6.1 The bonding section of the CFRM tendon shall be cleaned and rendered free from any grease, dirt etc. 6.2 Suitable measures shall be taken before placing to prevent bonding of the non-bonding sections of the tendon, and the CFRM tendon shall be placed horizontally in the form, perpendicular to the loading face. 6.3 The opening in the form through which the CFRM tendon is inserted must be sealed to prevent ingress of water etc. using oil putty or similar. 6.4 The form must be kept horizontal from the time of placing the concrete until the form is removed. - 121 -

6.5 After placing, the test piece shall be smoothed off by scraping any excess concrete off the top, repeating this process again after around 2 hours to ensure that a test piece of the proper dimensions is obtained.

7. REMOVAL OF FORMS AND CURING Forms shall be removed after 2 days, and the test pieces cured thereafter in water at a temperature of 20±3°C until the time of testing.

8. TESTING MACHINE AND DEVICES 8.1 Testing machine The testing machine for pull-out tests must be capable of applying the prescribed load accurately.

8.2 Loading plate The loading plate shall have a hole through which the CFRM tendon shall pass. The diameter of the hole in the loading plate shall be around 2~3 times the diameter of the continuous fiber tendon.

8.3 Anchorage The loading end side of the CFRM tendon shall be fitted with an anchorage capable of transmitting loads accurately until the tendon pulls out due to bond failure, or because of splitting or cracking of the concrete. The load transmission device shall transmit axial loads only to the CFRM tendon, without transmitting either torsion or flexural force.

8.4 Dial gauge The displacement meter fitted to the free end of the CFRM tendon shall be a dial gauge or similar apparatus, giving readings accurate to around 1/1000 mm.

9. TEST METHOD 9.1 Mounting of test piece The test piece shall be placed correctly on the loading plate, with a spherical plate underneath to prevent eccentric loads from acting on the test piece.

9.2 Loading rate The standard loading rate shall be such that the average tensile stress of the CFRM tendon increases at a 2 rate of 10~20 N/mm per minute. The loading rate must be kept as constant as possible, not subjecting the test piece to shock.

9.3 Scope of test The slippage of the free end and the load applied shall be recorded in the increments shown in table 2, until either the continuous fiber tendon pulls out of the concrete, or the load decreases significantly due to splitting or cracking of the concrete.

- 122 -

Table 2: Measurement increments Slippage of free end

Measurement increment

~0.1 mm

every 0.01 mm

0.1 mm ~ 0.2 mm

every 0.02 mm

0.2 mm ~ 0.5 mm

every 0.05 mm

0.5 mm ~

every 0.1 mm

9.4 Age of test piece The age of the test piece at the time of testing shall be 28 days.

10. CALCULATION AND EXPRESSION OF TEST RESULTS 10.1 Handling of data In cases where a test piece is judged to have undergone tensile failure at the anchoring section, or to have slipped out of the anchoring section before the CFRM has slipped from the concrete or the load is significantly reduced due to splitting or cracking of the concrete, the data shall be disregarded and additional tests shall be performed until the number of test pieces slipping from the concrete or where the load is significantly reduced due to splitting or cracking of the concrete is not less than three.

10.2 The bond strength shall be calculated according to Eq. (1) and rounded off to 3 significant digits and the curve for the pull-out load or bond stress versus slippage displacement for each test piece shall be plotted.

τ =

P ul

(1)

where τ =

2

bond stress (N/mm ) P = tensile load (N) u = nominal peripheral length of CFRM (mm) l = bonded length (mm)

10.3 The average bond stress causing slippage at the free end of 0.05 mm, 0.10 mm and 0.25 mm, and the maximum bond stress at the failure load shall be calculated.

11. TEST REPORT

- 123 -

The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber, type of surface treatment of fibers (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, nominal cross sectional area (5) Date of test, test temperature, loading rate (6) Dimensions of test pieces, bonded length of CFRM (7) Concrete mix, slump, and compressive strength at time of testing (8) Average bond stress causing slippage at the free e nd of 0.05 mm, 0.10 mm and 0.25 mm for each test piece (9) Maximum bond stress, failure mode and averages for each test piece (10) Bond stress - slippage displacement curve for each test piece

- 124 -

TEST METHOD FOR SHEAR PROPERTIES OF CONTINUOUS FIBER REINFORCING MATERIALS BY DOUBLE PLANE SHEAR (JSCE-E 540-1995)

1. SCOPE This specifications specifies mainly the test method for shear properties of CFRM used in place of steel reinforcement or prestressing tendon in concrete, by direct application of double shear.

2. TEST PIECES 2.1 Preparation of test pieces Test pieces shall as a rule not be subjected to any processing. For mesh-type CFRM, linear test pieces may be prepared by cutting away extraneous parts in such a way as not to affect the performance of the part to be tested. Test pieces should be as straight as possible; severely bent pieces should not be used.

2.2 Handling of test pieces During the obtaining and preparation of test pieces, all deformation, heating, outdoor exposure to ultraviolet light etc. causing changes to the material properties of the test section of the test piece must be avoided.

2.3 Length of test pieces Test pieces shall be of constant length regardless of the nominal diameter of the CFRM. Length shall not be less than 5 times the shear plane interval, and not more than 30 cm.

2.4 Number of test pieces The number of test pieces shall not be less than three. If the test piece shows significant pull-out of fibers, indicating that failure is not due to shear, an additional test shall be performed on a separate test piece taken from the same lot.

3. TESTING MACHINE AND DEVICES 3.1 Testing machine The testing machine to be used in load testing shall conform to JIS B 7733 (Compression Testing Machines). The testing machine shall have a loading capacity in excess of the tensile capacity of the test piece, and shall be capable of applying loading at the required loading rate. The testing machine must also be capable of giving readings of loading accurate to within 1% during the test.

3.2 Shear testing apparatus The shear testing apparatus shall be constructed so that a rod-shaped test piece is sheared on two planes more or less simultaneously by two blades (edges) converging along the faces perpendicular to the axial

- 125 -

direction of the test piece. The discrepancy in the axial direction between the upper and lower blades shall be of the order of 0~0.5 mm, and shall be made as small as possible. The specifications distance between shear planes shall be 50 mm.

4. TEST TEMPERATURE The test temperature shall generally be within the range 5~35°C. The specifications test temperature for test pieces sensitive to temperature shall be 20±2°C.

5. TEST METHOD 5.1 Mounting of test piece The test piece shall be mounted in the center of the shear apparatus, touching the upper loading device. No gap should be visible between the contact surface of the loading device and the test piece.

5.2 Loading rate 2

The specifications loading rate shall be such that the shearing stress increases at a rate of 30~60 N/mm per minute. Loading shall be applied uniformly without subjecting the test piece to shock.

5.3 Scope of test Loading shall be continued until the test piece fails, and the failure load recorded to three significant digits. It should be noted that loading may decrease temporarily, owing to the presence of two rupture faces.

6. CALCULATION AND EXPRESSION OF TEST RESULTS 6.1 Handling of data Whether the rupture surface is due to shear or not shall be determined by visual inspection. If pull-out of fibers etc. is obvious, the data shall be disregarded and additional tests shall be performed until the number of test pieces failing due to shear is not less than three.

6.2 Shear strength Shear strength shall be calculated according to Eq. (1), and rounded off to 3 significant digits.

τ =

P

2 A

(1)

where τ =

2

shear strength (N/mm ) P = shear failure load (N) 2 A = nominal cross sectional area of test piece (mm )

7. TEST REPORT - 126 -

The test report shall include the following items: (1) Name of CFRM (2) Type of fiber and fiber binding material, volume ratio of fiber (3) Numbers or identification marks of test pieces (4) Designation, nominal diameter, maximum cross sectional area (5) Date of test, test temperature, loading rate (6) Intervals between double shear faces (7) Shear failure load for each test piece, average shear failure load and shear strength (8) Failure mode of each test piece

- 127 -

COMMENTARY ON THE TEST METHOD FOR TENSILE PROPERTIES OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 531-1995) INTRODUCTION A test method for tensile properties of CFRM was first set out in a proposal by the JSCE ("The application of continuous fiber reinforcement materials to concrete structures", Concrete Library No. 72), followed by another proposal from the Architectural Institute of Japan ("Research on long fiber reinforced concrete (Report No. 3)"). These documents lie behind the test method proposed here. The test method given here focuses on the CFRM itself, excluding the performance of the anchorage. For this reason, test data clearly showing failure or pull-out at the anchoring section is to be disregarded, and test findings based solely on test pieces failing in the test section.

1. SCOPE Test pieces shall be linear or meshed CFRM formed from continuous fibers, matrices etc. as defined elsewhere and acting mechanically as a monolithic body.

2. DEFINITIONS Of the terms used here, nominal diameter and nominal cross sectional area are used as defined in the "Quality Standard for Continuous Fiber Reinforcing Materials". Guaranteed tensile capacity has been added to provide a basic standard for testing at some future date when a guaranteed tensile capacity has been determined.

3. TEST PIECES Tensile test conducted by various organizations has found that tensile strength ceases to vary in test pieces longer than 30 times their nominal diameter ( Fig.C 1). At lengths of 30 times the nominal diameter, however, the anchoring section is apt to fail, resulting in variations in strain readings. It was therefore decided to specify lengths of not less than 100 mm, and not less than 40 times the nominal diameter, with the additional condition for CFRM in strand form that the length should be not less than 2 times the strand pitch. This requirement corresponds to the requirements in JIS G 3536 (Uncoated Stress-relieved Steel Wires and Strands for Prestressed Concrete), JSCE "Standard Specification for Design and Construction of Concrete Structures" and AIJ "Prestressed Concrete Design and Construction Standards", all of which call for test pieces "not less than 100 mm for wire; not less than 200 mm for 2-core strands and deformed 3-core strands; not less than 600 mm for 7-core strands and 19-core strands; not less than 2 times the strand pitch for other types of strands; not less than 40 times

- 128 -

the basic diameter for multiple strands". The requirement also corresponds to the AIJ "Proposal for Tensile Breaking Strength Test for Long Fiber Reinforcing Materials" requirement for test pieces to be "not shorter than 300 mm", etc.

Fig. C 1

Effects of test length on tensile strength

The required numbers of test pieces were determined with reference to the statistical equation below:

N

=

(T

× CV / µ )

2

where N = number of test pieces T = statistical value (T = 1.96 when confidence level = 95%) µ =

accuracy (%) CV = coefficient of variation (%)

That is, when the data from the test pieces that failed in the test section in tests conducted by the various organizations, for test pieces with a test length of not less than 38 times the nominal diameter, when N = 5~15 the coefficient of variation CV for the breaking load was less than 5.8%, with an average value of 3.0%. Applying accuracy µ = 5% with a confidence level of 95% to these results, the maximum value of N is found to be 5.2, and the average value 1.4. Based on this, the number of test pieces was set to not less than 5.

4. TEST TEMPERATURE The standard test temperature for temperature-sensitive test pieces (i.e. test pieces showing a variation of more than 5% for failure tensile capacity, Young’s modulus or ultimate strain over a temperature range of 5~35°C) was set at 20±2°C.

- 129 -

5. TEST METHOD The gauge distance when using an extensometer was set at not less than 8 times the nominal diameter of the CFRM for linear materials, with an additional requirement for stranded materials that the gauge distance must be not less than the strand pitch. This sometimes results in a shorter gauge distance than that required in JIS G 3536 (Uncoated Stress-relieved Steel Wires and Strands for Prestressed Concrete), JSCE "Standard Specification for Design and Construction of Concrete Structures" and AIJ "Proposal for Tensile Breaking Strength Test for Long Fiber Reinforcing Materials", all of which call for a gauge distance of "not less than 100 mm", but the present requirement agrees with the gauge distance requirement in JIS G 3109 (Steel Bars for Prestressed Concrete) calling for a gauge distance "8 times the basic diameter of round bars, and 8 times the nominal diameter of deformed bars", and with the requirement in JIS Z 2201 (Test Pieces for Tensile Test for Metallic Materials; based on JIS G 3109) for a gauge distance of "3~8 times the diameter" of all types of rod-shaped test pieces. When a strain gauge is used, this shall be fitted correctly in the direction of tension, without damaging the test piece. If fitting the gauge in the direction of tension is not feasible, as with stranded materials, it should be fitted in accordance with some other appropriate method. The loading rate has been set at 100~500 N/mm2/min, or equivalent fixed strain loading. This falls within the loading rate prescribed in the AIJ "Proposal for Tensile Breaking Strength Test for Long Fiber Reinforcing Materials" ("300~3,000 N/mm2/min or 1%/min, whichever is the lesser"), and also falls within the ISO prescription of ("1~10 N/mm2/sec (60~600 N/mm2/min) for materials having a Young’s modulus not greater than 1.5×103 N/mm2") in the ISO standards for test methods for metallic materials. In AFRP rods, the range of loading rates corresponding to the above (0.2~0.9%/min), the variation in tensile strength is less than 1%, therefore these loading rates are deemed appropriate (Fig.C 2).

Fig. C 2

Effects of loading rate on tensile strength

6. CALCULATION AND EXPRESSION OF TEST RESULTS (1) CFRM show elastic behavior in all zones leading to failure in many cases the Young’s modulus varies depending on the load; in carbon and Aramid fiber reinforcement materials, significant variation in the Young’s modulus is found in the region under 20% of the tensile capacity (Fig. C 3). Since the load range in actual service is below 60% of the tensile capacity, it was decided to derive the Young’s

- 130 -

modulus from the secant gradient of the str ain-load curve at 20% and 60% of the tensile capacity. If a guaranteed tensile capacity is set for the CFRM in question, or if the manufacturer can guarantee a specified tensile capacity, calculations can be based on the secant gradient at 20% and 60% of the guaranteed tensile capacity, rather than the tensile capacity. in Aramid CFRM, the Young’s modulus under repeated loading is greater than that on virgin loading, although in the present test method, only the virgin loading is taken into account (Fig. C 4)

Fig. C 3

Fig. C 4

Effects of load on Young’s modulus

Effects of repeated loading on Young’s modulus

(2) Where strain can be accurately measured up to failure using a strain gauge or similar apparatus, it was decided to identify ultimate strain with the strain corresponding to the tensile capacity. This ultimate strain corresponds to the ultimate strain used in design. Conversely, if strain cannot be accurately measured up to failure using a strain gauge or similar apparatus, ultimate strain is extrapolated based on the Young’s of elasticity and the tensile capacity. This method results in errors for materials (Aramid etc.) where the Young’s modulus varies with the load, and the value obtained is

- 131 -

around 5% greater than the measured ultimate strain. Extrapolated ultimate strain, strictly speaking, is not identical with the failure strain, but the variation is minor and the value can safely be substituted for failure strain for design purposes.

REFERENCES 1) Section III, "DOCUMENTATION" of the present volume 2) Kakibara, Kamiyoshi and Kawasaki: Dynamic Characteristics of AFRP Rods, Proceedings of Symposium on Application of CFRM to Concrete Structures, pp. 79~82, 1992 3) Uomoto and Nishimura: Static Strength and Elastic Modulus of FRP Rods, JSCE Papers, No. 472/V-20, pp.77~86, 1993

- 132 -

COMMENTARY ON THE TEST METHOD FOR FLEXURAL TENSILE PROPERTIES OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 532-1995) INTRODUCTION When CFRM manufactured as straight rod is tensioned after being bent, the bending stress, added lateral pressure etc. may cause reduction of strength. When uni- directionally strengthened CFRM is bent for use as tendon in prestressed concrete, it is important to be aware of the relationship between the bending conditions and the strength characteristics. However, no standard tests of this type have been established even for steel or plastic materials. The present test method was developed for CFRM bent up as external cables, or arranged in a curved layout as internal cables. The following standards were referred to in relation to the development of this test method: -Architectural Institute of Japan: "Annotated Design Guidelines for Cable Structures" -New Prestressed Concrete Bridge Structures Survey & Research Committee, Expressway Survey Commission: "Report on Research into New Prestressed Concrete Bridge Structures (Findings of Study of Utility and Applicability of External Cables)", March 1993

1. SCOPE The present test is a materials performance test designed to determine the effects of bending on CFRM manufactured as straight rod etc., as compared to the tensile capacity when the material is straight. Stirrups, spiral bars and other CFRM bent from the time of manufacture fall outside the scope of this test.

2. DEFINITIONS The bent section is also often known as a deviator. Likewise, the deflector is also known as a saddle, or a sheave if disk-shaped.

3. TEST PIECES (Comment on 3.1) Since the loading test on sections of the CFRM other than the bent sections is

identical to the tensile test, it was decided to require simply that "Test pieces shall be prepared and handled in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". If sheaths, protective tubes etc. form an integrated part of the CFRM, the integrated unit shall be regarded as a single CFRM, and ideally tests shall be carried out in conditions approximating service conditions. In such cases, though, the material, thickness and geometry of the sheath or protective tubing must be clearly stated in the report.

- 133 -

(Comment on 3.2) In the "Test Method for Tensile Properties of Continuous Fiber Reinforcing

Materials", the test section length deemed unaffected by the anchoring section is specified as "... not less than 100mm, and not less than 40 times the nominal diameter of the CFRM. For CFRM in strand form, as an additional condition, the length shall not be less than 2 times the strand pitch.". For the purposes of flexural tensile test, this is the minimum distance required between the anchoring section and the bent section, therefore the specification is altered to read "The length of the test section shall not be less than 100mm from the anchorage to the bent section, and not less than 40 times the nominal diameter of the CFRM. For CFRM in strand form, as an additional condition, the length shall not be less than 2 times the strand pitch.". If the bent section is located in the center of the test section, then, the test section shall be more than twice as long as in tensile test. The length of test sections for multi-cables consisting of multiple strands of CFRM, the test length required is around 3 m, following the "Test Method for Performance of Anchorages and Couplers in Prestressed Concrete using Continuous Fiber Reinforcing Materials".

4. TESTING MACHINE AND DEVICES (Comment on 4.5) The surface of the bent section in direct contact with the test piece must be robust

and smooth, with no grooves. If the geometry and material of the deflector to be used in actual service has been decided, however, or if the present test is to be conducted for the purpose of determining the service geometry and material, the proposed deflector should be used in test. The geometry and material of the deflector must also be clearly noted in the report together with the test results. No specifications are given for the bending diameter ratio, as this should be decided according to the intended use. As a guide, the bending diameter ratios of deflectors currently in service are normally in the order of 100~150.

5. TEST TEMPERATURE For CFRM incorporating sheathing or other protective treatment, or for deflectors with treated surfaces, the temperature effects of the protective material must be considered in the test.

6. TEST METHOD A typical test procedure is illustrated in Fig. C 1.1)~3). (Comment on 6.1) The dominant parameters in this test are the bending diameter, the bending angle

and the nature of the contact between the CFRM and the deflector. The test conditions must therefore be determined with these parameters clearly spelled out. In addition to tests involving 1-point bending, i.e. using a single deflector, tests using multiple deflectors to bend the test piece at two, three or more points could also be considered but the standard test presented here is a 1-point bending test where the effects of a single bending diameter and bending angle are easier to determine. Three-point tests etc. may also be conducted if the results can be made consistent with those for the 1-point test.

- 134 -

Fig. C 1

Typical bending tensile test set-ups (for reference) 1)~3)

REFERENCES 1) Kobayashi, Kato and Enomoto: Research on sheaths for FRP Tendons, Summary of AIJ annual meeting, C Structures II, pp. 45~46, Oct. 1990 2) Enomoto and Santo: Experimental Research on Bending Tensile Capacity of CFRP Strands, Proceedings of the 46th JSCE Annual Conference, Vol. 5., pp. 232~233, Sep. 1991 3) Tokumitsu, Hino, Maruyama and Mutsuyoshi: Anchoring Systems and Tensile Properties in Flexure of Multi-type CFRM used as External Cables, Concrete Engineering Annual Papers, Vol. 15, No.2, pp. 813~816, Jun. 1993 Doc. 1: Architectural Institute of Japan: "Annotated Design Guidelines for Cable Structures", Chap. 7 "Detailing" 7.3 "Curved Sections of Cables", pp. 100~105, Jun. 1994 Doc. 2: Akimoto, Yamagata and Arakawa: Development of Practical New Techniques for Prestressed Concrete, External Cable Methods, Prestressed Concrete Structure Design & Construction Guidelines, Prestressed Concrete Technology Association, 22nd Prestressed Concrete Technology Lecture Series (Feb. 1994)

- 135 -

COMMENTARY ON THE TEST METHOD FOR CREEP FAILURE OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 533-1995) INTRODUCTION Unlike reinforcement or prestressing tendon, CFRM may fail (creep failure) at strengths below the maximum static strength when subjected to a significant sustained stress for long periods. This creep failure strength varies according to the type of CFRM, therefore the creep failure strength must be evaluated when determining the level of tension in CFRM used as tendons. This is the reason for the inclusion of the present test method. The following standards were referred to in relation to the development of this test: -JSCE standard "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials" -JSCE standard "Test Method for Long-term Relaxation of Continuous Fiber Reinforcing Materials" JIS K 7115-1986 "Testing Method for Tensile Creep of Plastics" JIS K 7108-1987 "Testing Methods for Chemical Resistance of Plastics under Constant Tensile Load"" As with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", the object of this test is the CFRM itself, excluding the performance of the anchorage. For this reason, test data clearly showing failure or pull-out at the anchoring section is to be disregarded.

1. SCOPE Test pieces shall be linear or meshed CFRM formed from fiber materials and matrices as defined elsewhere and acting mechanically as a monolithic body.

2. DEFINITIONS The creep failure capacity and creep failure strength for the design of concrete structures using CFRM are defined.

3. TEST PIECES (Comment on 3.1) Except for the fact that the load applied to the test piece is a constant, sustained

load, the loading state is similar to that in tensile test, therefore the test pieces for this test are to be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". (Comment on 3.2) Given the long periods of time required for creep test, it has been decided to

- 136 -

specify 3 test pieces per test condition.

4. TESTING MACHINE AND DEVICES (Comment on 4.1) Various types of testing machine may be used, such as hydraulic servo load testers,

dead-weight load testers etc. It should be noted, however, that in multiple creep testing machines the load applied to one test piece and the deformation, vibration etc. of the testing machine frame due to the load at the time of failure of one test piece are easily transmitted to other test pieces; the testing machine used should be designed and manufactured to eliminate this kind of interference.

5. TEST TEMPERATURE Creep behavior is easily affected by temperature, therefore a test temperature of 20±2°C is required, in accordance with the specification for temperature-sensitive materials in "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

6. TENSILE FAILURE CAPACITY This is the standard load from which the constant load to be applied continuously to the test pieces is determined; derived from the values for 5 test pieces.

7. TEST METHOD 7.3 Loads applied (Comment on (1) & (2)) The aim of this test is to extrapolate the creep failure capacity ratio at 1

million hours from the approximation line plotted according to 8.3 on the basis of test results up to 1000 hours. This requirement is included to increase the accuracy of the approximation line.

Tensile creep failure curves for various types of FRP (fiber reinforced plastic) are shown in Fig. C 1. Creep failure strength is given as a stress ratio, based on the tensile strength. CFRP using carbon fibers show high creep failure strengths of around 90% at 1000 hours, while GFRP made from glass fiber show values of 65~70%. While these FRP are not used directly for reinforcement of concrete as CFRM, the values shown here are given for reference in setting the load ratio or sustained loads in creep failure test.

(Comment on 7.4) This section specifies the measurement intervals for creep strain if automatic

recording is not available. The intervals specified are the same as those in the "Test Method for Long-Term Relaxation of Continuous Fiber Reinforcing Materials".

- 137 -

Fig. C 1

Tension creep failure curves for various FRP

8. CALCUALTION AND EXPRESSION OF TEST RESULTS (Comment on 8.1) This provision is included to improve the accuracy of the approximation curve

given in 8.3. (Comment on 8.2 & 8.3) A semi-logarithmic graph such as that shown in Fig. C 2 is plotted, with a

horizontal axis showing elapsed time in hours on a logarithmic scale, and a vertical axis showing stress ratio on an arithmetic scale.

Fig. C 2

Creep failure curve

(Comment on 8.4) Creep failure capacity and creep failure strength normally refer to the values after

1 million hours (approximately 114 years), but if the service life of the proposed structure using

- 138 -

CFRM is determined in advance, the values correspond to this service life (i.e. the service life creep failure capacity and the service life creep failure strength).

REFERENCE 1) Introduction to FRP (revised), Reinforced Plastics Association, p.110, 1989

- 139 -

COMMENTARY ON THE TEST METHOD FOR LONG-TERM RELAXATION OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 534-1995) INTRODUCTION Tendon relaxation in prestressed concrete structures is an important factor that has to be considered in the design. relaxation measurements in keeping with the intended purpose therefore must be made for CFRM, according to the method given here. In Japan, currently the only prescriptions for relaxation test of prestressing tendon are the 10-hour tests given in JIS G 3536 (Uncoated Stress-relieved Steel Wires and Strands for Prestressed Concrete), and in JIS G 3109 (Steel Bars for Prestressed Concrete). These deal only with mechanical properties as quality standards, and do not give meaningful data for design purposes, which can only be obtained from long-term test conducted at a constant, normal temperature and with constant strain. To meet this need, the JSCE and the AIJ have conferred to produce the “Relaxation Test Method for Prestressing Steels” (AIJ/JSCE, JSEC-E 502-1990), correlated with the JIS test methods. A provisional long-term relaxation test method for CFRM based on the JSCE standard referred to above is proposed in Vol. 72 of the Concrete Library. The method presented here incorporates subsequent amendments made to ensure consistency with other test methods for CFRM.

1. SCOPE These provisions relate to a test method for determining levels of long-term relaxation of CFRM under a given temperature and strain, in order to give design-relevant data relating to prestressed concrete structures. Relaxation testing outside of the normal temperature range, and relaxation under variable strain, are therefore outside the scope of this test method, the purpose of which is also different from the existing 10-hour relaxation tests conducted for quality control of prestressing tendon. "Normal temperature" is defined here as a range of 20±15°C, following the Standard Temperature Class 4 given in JIS Z 8703. The test described here may be conducted at any temperature within this range, provided the temperature variation for the duration of the test is not more than ±2°C.

2. DEFINITIONS A definition is given here for the failure capacity, since this is required as the basis for determining the initial load applied to the test piece for the purposes of relaxation test.

3. TEST PIECES

- 140 -

(Comment on 3.1) Except for the requirement to maintain constant strain, the dynamic conditions for

test pieces are identical to those for tensile test, therefore the test pieces for this test are to be as for the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". (Comment on 3.2) Given the long periods of time required for relaxation test, it has been decided to

specify 3 test pieces per test condition.

4. TESTING MACHINE AND DEVICES (Comment on 4.1) The types of testing machine that may be used for this test include relaxation

testing machines, hydraulically controlled loading machines etc.

5. TEST TEMPERATURE Relaxation behavior is easily affected by temperature, therefore a test temperature of 20±2°C is required, in accordance with the specification for temperature-sensitive materials in "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". As some of the constituent materials of CFRM are highly temperature-sensitive, however, provision has been made for additional tests to be carried out at 0°C and 60°C if necessary.

6. TEST METHOD (Comment on 6.2) Prestretching is carried out prior to relaxation tests in order to attune the test piece

to the testing machine and / or the strain gauge. It has been noted, however, that in Aramid fibers the relaxation rate is affected by the method of loading employed. In such cases, prestretching levels and times must be kept to a minimum. (Comment on 6.3) The purpose of this test is to determine the relaxation rates required for design

purposes, and the initial load must therefore be set to the rate in actual service conditions. This conditions may in some cases result in a load that falls within a range where creep failure occurs but not failure due to relaxation; in such cases, it must be confirmed under actual loading conditions that the load does not result in creep failure of the CFRM, increasing the initial load as necessary. (Comment on 6.4) Application of initial load

The previous version of this proposed method gave the loading rate as a function of the fiber content by volume, but this has now been brought in line with the tensile test method.

7. CALCULATION AND EXPRESSION OF TEST RESULTS A semi-logarithmic graph such as that shown in Fig. C 1 is plotted, with the horizontal axis showing elapsed time in hours on a logarithmic scale, and the vertical axis showing relaxation rates on an arithmetic scale.

- 141 -

Fig. C 1

Typical relaxation test results

8. TEST REPORT In normal testing, prestretching should not influence the results of the test, but if such influence is suspected, the report should include details of the level, time and method of prestretching.

- 142 -

COMMENTARY ON THE TEST METHOD FOR TENSILE FATIGUE OF CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 535-1995) INTRODUCTION The test method presented here is based on the JSCE "Test Method for Fatigue of Continuous Fiber Reinforcing Material (Tentative Proposal)", published in Vol. 72 of the Concrete Library, April 1992. Given the need to confirm the fatigue characteristics of CFRM used in concrete structures subject to prevailing repeated loads due to traffic, wave action etc., the April 1992 proposal is presented as a fatigue test method for isolated CFRM, with reference to JIS K 7118 "General Rules for Testing Fatigue of Rigid Plastics", JIS K 7119 "Testing Method of Flexural Fatigue of Rigid Plastics by Plane Bending, JIS Z 2273 "General Rules for Fatigue Testing of Metals", and the JSCE standard "Proposed Method for Fatigue Testing of Reinforcement Joints”. The method given here is a revised version of the April 1992 proposal, narrowed down to tensile fatigue test as this is the most fundamental test, with reference to JIS K 7083 "Testing Method for Constant-Load Amplitude Tension - Tension Fatigue of Carbon Fiber Reinforced Plastics". Ideally the fatigue characteristics of CFRM in concrete structures should be tested on concrete members incorporating the CFRM, but as such tests would have to be done on a large scale and are unsuitable for accumulation of data, it was decided to set up a fatigue test method for isolated CFRM. Once a certain quantity of data has been accumulated, tests using concrete members to confirm fatigue characteristics will also be necessary.

1. SCOPE Test pieces shall be linear or meshed CFRM formed from continuous fibers, matrices etc. as defined elsewhere and acting mechanically as a monolithic body. Various forms of fatigue test are possible, such as tension-tension, tension-compression, compression-compression testing etc., and various methods of loading are also possible, but it has been decided to define the present test as a tensile and tensile fatigue test under constant cycle load, this being considered the most basic method for evaluating material characteristics.

2. DEFINITIONS Definitions of terms for this test shall follow those given in the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", with reference also to JIS K 7083 " Testing Method for Constant-Load Amplitude Tension - Tension Fatigue of Carbon Fiber Reinforced Plastics ". (Comment on (1)~(6)) As testing machines are load-controlled, the term load is used in the

description of the test, although the term stress is more usual in reporting of results. In the context of

- 143 -

this test, therefore, both terms are used interchangeably (see Fig. C 1).

Fig. C 1

Repeated load (/repeated stress) 1)

(Comment on 8) The number of cycles is represented by N or n, where N is the number of cycles to

fatigue failure, and n is the number of cycles carried out during fatigue testing. (Comment on 9) If the test piece has not failed by the end of the test, this fact is to be indicated by the

addition of an arrow at the right-hand end of the curve (see Fig. C 2). The vertical axis of the S-N plot may represent repeated maximum stress ( σmax), stress range (∆σ), stress amplitude (σa) etc., depending on the purpose of the test. "Stress" may be replaced by "load" depending on the purpose of the test.

Fig. C 2

Typical S-N plot

(Comment on 10) Fatigue strength is generally taken to be a generic term for fatigue limit and fatigue

strength at N cycles, where the fatigue limit specifically refers to the point at which the S-N curve becomes parallel to the horizontal axis (representing number of cycles). Fatigue strength at N cycles is the upper limit for the repeated stress that can be borne by the test piece over a specified number of cycles (N). While fatigue limits are recognized for steel materials, for plastics and FRPs the S-N curve continues to slope downwards even after 108 cycles. So-called fatigue limits are therefore considered not to exist for these materials, and the maximum stress at which the material does not fail after N cycles is substituted for the fatigue limit. That is, this fatigue limit is equivalent to fatigue strength at N cycles, and for CFRM also, the maximum stress at which the material does not fail after N cycles is substituted for the fatigue limit. Fatigue strength i s indicated with the number of cycles N appended in parentheses, e.g. σm (2×106). - 144 -

(Comment on 11) The unit normally used is Hz.

3. TEST PIECES (Comment on 3.1) Except for the fact that the load acting on the test piece is a constant load applied

repeatedly, the loading conditions for test pieces are similar to those for tensile test, therefore the test pieces for this test are to be in accordance with the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials". (Comment on 3.2) The requirement for at least three (3), for each of at least three (3) levels of loading

/ stress is imposed to ensure proper plotting of the downward-sloping S-N curve, but if the S-N curve cannot be properly plotted because of unsuitable stress level settings or wide variations in data, additional test must be performed as necessary. The static tensile strength on which the loading levels for this test are based should be calculated on the basis of not less than five tests conducted according to the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials", using identical test pieces to those used in the fatigue test.

4. TESTING MACHINE AND DEVICES (Comment on 4.1) The testing machine should preferably be fitted with an automatic load

maintenance mechanism. If a test machine with electrohydraulic control is to be used, steps must be taken to ensure the knobs on the excitation side are fixed, i.e. cannot rotate during the test (see Fig. C 3).

Fig. C 3

Typical testing machine

(Comment on 4.2) Some reports indicate that the type of anchorage device used has a greater effect

on the test results in fatigue test than in tensile test, and this issue remains to be studied. Provisionally,

- 145 -

therefore, the anchorage used should be identical in all tests.

5. TEST TEMPERATURE As the effects of temperature and humidity on fatigue tests remains to be clarified, the provision given here is based on the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials".

6. TEST METHOD (Comment on 6.1) If any slight horizontal movement or rotation of the knob on the excitation side of

the test machine is noted, fitting of a guide to prevent such movement before the test is performed may minimize or eliminate any variations in data.

(Comment on 6.2) If the effects of creep failure strength on the tensile fatigue strength are known in

advance, this should be taken into account in the setting of the test load and the frequency. Typical S-N curves for FRP using various types of fibers are shown in Fig. C 4, where the maximum-minimum stress ratio R is fixed at 0.1. As the fatigue life (i.e. number of cycles to fatigue failure) is generally affected not only by the maximum stress ratio, but also by the stress amplitude, different results may be obtained is the maximum and minimum stress ratios vary. In actual concrete structures subject to variable loads, permanent loads such as dead weight etc. can be considered as the minimum load, and the design load can be considered as the maximum load. In almost all cases, the maximum-minimum stress ratio R is greater than the value adopted in Fig. C 4, therefore the S-N curve obtained in such a case can be taken to be more conservative than that shown in Fig. C 4.

Fig. C 4

Typical S-N curves for various FRP

The following procedure may be employed where the maximum stress level for the initial test is difficult to determine: (1) Select an appropriate stress level in the range 20~60% of the static tensile strength, and commence

- 146 -

fatigue test with this value as the repeated maximum stress. (2) If the test piece is still did not fail after 104 cycles at this repeated maximum stress, add 5% of the static tensile strength to the repeated maximum stress, and perform the test using the same test piece. In this case, if possible the test should be carried on uninterruptedly, with the repeated maximum stress incorporating 5% of the static tensile strength. (3) If the test piece still did not fail after a further 104 cycles following step (2), a further 5% of the static tensile strength should be added to the repeated maximum stress. (4) Repeat step (3) until the test piece fails. (5) The initial tensile-tensile fatigue repeated maximum stress should be set at the repeated maximum stress level where the test piece fails, minus 5% of the static tensile strength. (Comment on 6.3) The frequency is set to eliminate the effects of inertia of the moving parts of the

test machine, with an upper limit placed at the frequency to prevent excessive heating of the test piece. The entire series of tests should preferably be performed with the same frequency. If the frequency is too low the test will be prolonged accordingly, while if the frequency is too high, the effects of heating will accelerate fatigue damage of the test piece, thus reducing the number of cycles to failure. Further limitations are imposed by the capacity of standard testing machines etc. For these reasons, the frequency has been set at 1~10 Hz, based on previously conducted tensile fatigue tests on CFRM. Depending on the type of CFRM and the stress level, heating may occur even in this range. If heating is suspected, the frequency should be kept below 5 Hz, and the temperature of the test piece should be monitored. (Comment on 6.4) It should be noted that load variation may occur during a test due to variations in

the rigidity of the test piece. If the test machine is not equipped with an automatic load maintenance mechanism, the load must be checked and corrected as necessary during the test. n

5

(Comment on 6.5) The number of cycles is expressed as a multiple of 10 , e.g. 2.34×10 , rounded off

to three significant digits. The maximum value for the number of cycles to failure (i.e. the number of cycles at which the test may be halted) i s 2×106.

7. CALCULATION AND EXPRESSION OF TEST RESULTS (Comment on 7.2) In the case of repeated loading, the stresses corresponding to the maximum and

minimum loads respectively are the maximum repeated stress ( σmax) and the minimum repeated stress (σmin). Which of the terms load and stress is used will depend on the purpose of the test. In fatigue test with constant average load or constant minimum repeated load, the relationship generally sought is that between maximum repeated stress or stress amplitude, and the number of cycles to failure (the S-N curve). For some test purposes, though, fatigue strength after a given number of cycles may be plotted with stress amplitude on t he vertical axis and average stress on the horizontal axis, or with maximum stress on the vertical axis and minimum stress on the horizontal axis. In the present test, it is hard to draw a distinction between tensile fatigue strength and creep failure strength; this issue awaits further study. In the calculation and expression of test results, therefore, the number of cycles and the repetition rate, i.e. the length of time the repeated load is applied, must be

- 147 -

made clear. Where the creep failure strength is known, this may be plotted in a fatigue strength graph etc.

8. TEST REPORT (Comment on 6) If the test piece did not fail or the test is halted after the specified number of cycles,

this fact should be noted in the test report. For cases of failure other than normal failure, the condition of the test piece during the test, and the mode of failure, should also be noted.

REFERENCE 1) JIS K 7083 " Testing Method for Constant-Load Amplitude Tension - Tension Fatigue of Carbon Fiber Reinforced Plastics "

- 148 -

COMMNETARY ON THE TEST METHOD FOR COEFFICIENT OF THERMAL EXPANSION OF CONTINUOUS FIBER REINFORCING MATERIALS BY THERMOMECHANICAL ANALYSIS (JSCE-E 536-1995) INTRODUCTION The test method presented here is based on the JSCE "Test Method for Thermal Expansion Coefficient Testing of Continuous Fiber Reinforcing Material (Tentative Proposal)", published in Vol. 72 of the Concrete Library, April 1992, which was based on JIS C 2141 "Testing Methods of Ceramic Insulators for Electrical and Electronic Applications", as the coefficients of thermal expansion of CFRM are relatively close to those of ceramics. Subsequent investigations with commercially available testing machines for measuring thermal expansion coefficients revealed that the TMA machine is the most widely available machine, and furthermore requires no particular expertise in handling. JIS standards have already been established for thermal expansion coefficient test of plastics using the TMA and the technique has been confirmed to be sufficiently accurate. These facts have been borne in mind in drawing up the present test method. The following standards are referenced: JIS R 3102-1993 "Test Method for Average Linear Thermal Expansion of Glass" JIS K 7197-1991 "Testing Method for Linear Thermal Expansion Coefficient of Plastics by Thermomechanical Analysis" JIS K 7100-1981 "Standard Atmospheres for Conditioning and Testing of Plastics" JIS B 7502-1979 "Micrometer Calipers"

1. SCOPE This test using the TMA device is to be applied to linear or meshed CFRM test pieces formed from continuous fibers, matrices etc. as defined elsewhere and acting dynamically as a monolithic body.

2. DEFINITIONS (Comment on 1) A non-vibrating load refers to a load applied slowly enough to prevent the load

changes over time from being affected by the viscoelasticity of the material. (Comment on 3) Coefficient of thermal expansion is generally defined as a value obtained by dividing the differential of the ratio between the length change and temperature change at a given temperature (dL/dT ) by the length of the test piece as measured at room temperature. Strictly speaking, however, the length of the test piece ∆ L in relation to a finite temperature difference ∆T is a measured variable rather than a differential value, hence the term average coefficient of linear thermal expansion at representative temperatures.

- 149 -

3. TEST PIECES (Comment on 3.1) Unlike metals, inorganic materials etc., in plastics the dimension changes due to

adsorption and desorption of moisture, or to the release of residual strain during molding, processing etc. are not negligible in comparison to the linear thermal expansion. In order to ensure the reliability of measurements, provision has therefore been made for curing of CFRM based on JIS K 7100 "Standard Atmospheres for Conditioning and Testing of Plastics ", with the aim of eliminating moisture and strain resulting from molding and processing. Clearly, if pre-test curing is inadequate, the test piece will shrink due to desorption of moisture as the temperature rises, resulting in an exaggerated value being obtained for the coefficient of t hermal expansion. (Comment on 3.2) The length of the test piece is based on JIS R 3102 "Test Method for Average Linear Thermal Expansion of Glass", where out of consideration for the capacity of the testing machine the standard length is set at no more than 20±0.025 mm, and the diameter or length of one side is set at no more than 5 mm. If a test piece of such dimensions is difficult to obtain from the CFRM in question, test pieces of different dimensions may be used.

4. TESTING MACHINE (Comment on 4.1) A standard TMA apparatus allows measurements in various modes - expansion,

compression, penetration, tension etc. - depending on the choice of loading method and the geometry of the detector rod, but the test described here will normally be conducted in compression mode. A typical TMA apparatus is illustrated in Fig. C 1.

Fig. C 1

Configuration of a typical TMA apparatus

(Comment on 4.2) As the accuracy of measurements of the coefficient of thermal expansion is

intimately connected with the accuracy of temperature measurements, temperature calibration is

- 150 -

particularly important. Temperature calibration materials feasible for this test would include ice water (0°C) for low temperature calibration, and indium (melting point 156.4°C) for high temperature calibration. (Comment on 4.3) The TMA apparatus should preferably be mounted on a vibration-proofing base

during the test, to eliminate the effects of vibration.

5. TEST METHOD (Comment on 5.1) As measurement accuracy in the order of µ m is required to ascertain dimensional changes, care must be taken to remove extraneous materials such as grease, and to mount the test piece

stably. (Comment on 5.4) The service temperature range for CFRM in actual service is assumed to be

0~60°C. If service temperatures are expected to fall outside this range, the test temperature range must be extended accordingly. (Comment on 5.5) A limit has been imposed on the rate of temperature increase to minimize

temperature measurement errors resulting from the temperature increasing too rapidly. (Comment on 5.6) According to JIS K 7197 "Testing Method for Linear Thermal Expansion

Coefficient of Plastics by Thermomechanical Analysis", the compressive stress acting on the tip of the detector rod is to be in the order of 3±0.1 mN/mm2, and this standard has been referenced in setting the compressive stress acting on the test piece at around 3 mN/mm 2. This requirement need not apply if the effects on measurements within the test temperature range of softening of the matrix are minimal.

6. CALCULATION AND EXPRESSION OF TEST RESULTS The coefficient of thermal expansion of unidirectional fiber-reinforced plastics along the fiber axis is approximated by the following equation according to compounding:

α F =

( E f α f V f

+

E mα mVm ) / ( E fV f

+

E mV m )

( Eq. C 1)

where α F =

coefficient of thermal expansion of unidirectional fiber-reinforced plastics along the

fiber axis α f =

coefficient of thermal expansion of fiber material αm = coefficient of thermal expansion of matrix E f = modulus of elasticity of fiber material E m = modulus of elasticity of matrix V f = fiber material content by volume V m = matrix content by volume As the Young’s modulus of the fiber binding material is generally very small compared to the Young’s modulus of the fiber material, the coefficient of thermal expansion of unidirectional fiber-reinforced plastics along the fiber axis will be close to the coefficient of thermal expansion of fiber material.

- 151 -

Similarly, the coefficient of thermal expansion perpendicular to the fiber axis is approximated by the following equation: α Fr =

(1 + Vm )α mVm + (1 + V f )α f V f

−

F

(v f V f

+ v mVm )

( Eq. C 2)

where = coefficient of thermal expansion of unidirectional fiber-reinforced plastics perpendicular to the fiber axis v f = Poisson's ratio of fiber material V m = Poisson's ratio of matrix α Fr

Approximate values obtained for various fiber materials and CFRM using them are listed in Table C 1. It can be seen from the table that, since the coefficient of thermal expansion of unidirectional fiber-reinforced plastics along the fiber axis is approximately equivalent to that of the fiber material, the coefficient of thermal expansion of the fiber material may be substituted for that of the unidirectional fiber-reinforced plastic along the fiber axis. As few measurements have been made of the coefficient of thermal expansion of CFRM perpendicular to the fiber axis, an example for one type of unidirectional fiber-reinforced plastic is also given in the table (1). The coefficient of thermal expansion perpendicular to the fiber axis is extremely high in relation to that in the axial direction, and tends to approach the order of magnitude of the coefficient of thermal expansion of the fiber binding material. Table C 1: Approximate values for coefficient of thermal expansion

Material Carbon Aramid Glass Epoxy Unsaturated Polyester Steel Concrete

Fiber -2 ~ 8 -8 ~ -3 8 ~ 10

Coefficient of Thernal Expansion ( × 10-6/°C) CFRM or Other Materials Longitudinal Direction Transverse Direction 0.6 ~ 1 25 -6 ~ -2 30 8 ~ 10 23 55 ~ 60 80 ~ 100 12 7 ~ 12

REFERENCE 1) H. Miyairi et al. (ed.) Dictionary of Composite Materials, Asakura Shoten publishers, pp.278~279, 1991

- 152 -

COMMENTARY ON THE TEST METHOD FOR PERFORMANCE OF ANCHORAGES AND COUPLERS IN PRESTRESSED CONCRETE USING CONTINUOUS FIBER REINFORCING MATERIALS (JSCE-E 537-1995) INTRODUCTION Some studies have been made on test methods for anchorages for use with CFRM tendons in prestressed concrete as part of the Joint Research on New Materials for Use as Tendons in Prestressed Concrete Bridges, which in turn is a part of the Ministry of Construction Comprehensive Technology Development Project for Construction-related New Materials Utilization. The present test method references the following standards, among others: JSCE "Standard Specification for Design and Construction of Concrete Structures" (1991 edition) JSCE "Prestressed Concrete Design and Construction Guidelines" (Concrete Library No. 66)

1. SCOPE The present test proposal is to be applied to anchorages and couplers for CFRM in prestressed concrete structures or members constructed by pre- or post-tensioning. Detailing of tests for special structures subject to unusual loads, located in unusual environments etc. must therefore be determined as appropriate for the structure in question, based on the test method given here. The anchoring methods currently in use include anchoring of diagonals in cable-stayed bridges, ground anchors etc., but these are not covered in the present test. Anchorage and coupler performance after long periods of use, fatigue performance etc. are also not covered by this test, as these are expected to be influenced by relaxation of the CFRM etc.

2. DEFINITIONS Terminology for this test is based on the "Recommendation for Design and Construction for Concrete Structures using Continuous Fiber Reinforcing Materials" and the "Quality Standard for Continuous Fiber Reinforcing Materials", with certain additions relating to CFRM used as tendons etc. CFRM used as tendons in prestressed concrete are referred to here as CFRM tendons.

3. TEST METHOD FOR PERFORMANCE OF ANCHORAGES 4. TEST METHOD FOR PERFORMANCE OF COUPLERS 5. TEST METHOD FOR PERFORMANCE OF ANCHORING SECTIONS

- 153 -

The test methods given are based on the JSCE "Proposed Performance Test Methods for Anchorages and Couplers used in Prestressed Concrete Construction", with extra provision being made in sections 3 and 4 for testing of anchorage and coupler performance, expressed in terms of tensile capacity. The "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials" is referenced with regard to the loading rate, test temperature, and number of test pieces. Tests 3 and 4 are intended for newly developed devices and devices with a minimal performance record in testing the performance (capacity) of anchorages and couplers. Test 5 is intended to check the performance of an anchoring section comprising and anchorage, anchorage reinforcement etc., focusing in particular on the performance of the surrounding concrete. Test 5 is thus to be used in checking the performance of an anchoring section designed using anchorages checked according to tests 3 and 4. The standard length of CFRM has been set at 3 meters. This is because CFRM anchorages and couplers are commonly used in so-called multi-types, where multiple CFRM are anchored or connected, and if the individual CFRM are of diverse lengths or incorrectly set at the time of tensioning, the tension will be concentrated on a small number of them which will consequently rupture (fail) before the others, giving inaccurate test results. This is best avoided by making the CFRM as long as possible, but as the test results should be on the conservative side, giving a low tensile capacity, and as the members actually used in prestressed concrete will be longer than 3 meters, this was selected as the standard length for the test. If the test does not involve multiple CFRM, the CFRM length may be shorter than 3 meters, but the minimum length given in the "Test Method for Tensile Properties of Continuous Fiber Reinforcing Materials" must be adhered to. (Comment on 3.4, 4.4) If one end of the CFRM or other tendon is fitted with an anchorage or coupler

other than the type to be tested, the performance of the other anchorage or coupler must first be confirmed to be equivalent or superior to that of the anchorage or coupler to be tested. (Comment on 3.5, 4.5) Mode of failure here refers to the condition of the test piece at which the

tensile capacity is reached, e.g. "failure of CFRM (giving location of rupture)", "pull-out of CFRM from anchorage", etc.

Fig. C 1

Test piece & loading method

- 154 -

(Comment on 5.2.1) The minimum allowable distance in determining the length of one side of the

concrete test piece can be obtained by reference to "Duyvidag Method Design and Construction Guidelines", Chapter 4 "Structural Detailing", 4.1 " Minimum Layout Distances", in JSCE "Prestressed Concrete Design and Construction Guidelines". (Comment on 5.2.2) As the proportion of steel and CFRM arranged in the anchorage reinforcement

will vary depending on the design, test conditions should approximate the actual design as closely as possible. Further, as the quantities of anchorage reinforcement reinforcement and additional bars installed relative to the proposed anchorage will also depend on the actual design, the quantities in the test piece should follow the actual design. (Comment on 5.2.3, 5.3.2) JSCE "Proposed Performance Test Methods for Anchorages nad Couplers

used in Prestressed Concrete Construction" requires that concrete strength strength at the time ti me of test should be "... sufficient to bear the prestressing level prescribed for the anchorage. Concrete strength at time of testing must not exceed the design strength." The present test requires compressive compressive strength at 28 days 2 of 30±3 N/mm , with the test being performed when the concrete has reached a compressive strength of 24±3 N/mm2. The reason for this is that the performance performance test proposed proposed here here is considered as a means of checking the performance of the anchorage, i.e. a separate test. The requirement for loading when the concrete has reached a compressive compressive strength of 24±3 N/mm2 is based on the general practice of prestressing at compressive strengths of 21~24 N/mm2. Concrete quality and the timing of loading may vary depending on the technique used, and in such a case, test conditions should be determined based on the proposed technique. (Comment on 5.3.1) Adequate safety measures should be in place when conducting tests involving

tensioning of tendons, owing to the inherent dangers of the technique.

6. TEST REPORT Mode of failure here refers to the condition of the test piece at which the tensile failure capacity is reached, e.g. "failure of CFRM (giving location of failure)", "pull-out of CFRM from anchorage", etc.

- 155 -

COMMENTARY ON THE TEST METHOD FOR ALKALI RESISTANCE OF CONTINUOUS FIBER REINFORCING MATERIALS MATERIALS (JSCE-E 538-1995) INTRODUCTION The need for the test for alkali resistance as a durability test for CFRM is referred to in Concrete Library No. 72 "Application of CFRM to Concrete Structures". The alkali resistance of CFRM is determined by immersing test pieces in an aqueous alkaline solution, noting any changes in external appearance, weight and tensile failure capacity before and after immersion, if necessary also conducting microscopic examination examination of the sides and sections of t he test piece, as well as physical and chemical analyses of the fiber bond. The present t est method references the following standards: -JIS K 7107 "Testing Methods for Chemical Resistance of Plastics under Constant Tensile Deformation" -JIS K 7108 "Testing Methods for Chemical Resistance of Plastics under Constant Tensile Load" -JIS K 7114 "Testing Method for Evaluation of the Resistance of Plastics to Chemical Substances" -JIS K 7209 "Testing Methods for Water and Boiling Water Absorption of Plastics"

1. SCOPE The purpose of this test is to evaluate the alkali resistance of CFRM.

2. TEST PIECES (Comment on 2.1) The length of the test section of test pieces is based on the proposed tensile test

method. Test pieces which have clearly failed at or slipped out from the anchoring section are to be ignored, and test continued until the number of test pieces failing in the test section is not less than three. As there is a possibility of alkaline fluid infiltrating via the ends of the test t est piece, causing loss of strength in the CFRM, both ends are to be completely sealed with a strong alkali-resistant resin such as epoxy. (Comment on 2.2) The epoxy sealed ends of a test piece that has undergone immersion are to be cut

off, giving a test piece for measurement of mass change. Following measurement of mass change, the test piece is to undergo tensile test.

3. IMMERSION IN ALKALINE ALKALINE SOLUTION (Comment on 3.1) The alkaline solution should be at around pH 13, e.g. Ca(OH)2 = 2 g/l g/l , NaOH = 10

g/l g/l , KOH = 14 g/l g/l . During long-term testing, there is a possibility of water in the alkaline solution

- 156 -

evaporating or absorbing CO2 from the air, resulting in changes of composition and pH levels, as well as sedimentation. Immersion has therefore to be carried out in a sealed container. Any elution or reaction with the alkali on the part of the CFRM may be ignored, as the high pH level renders negligible the effects of elution or reaction on the pH level. (Comment on 3.2) A high hi gh temperature is desirable as this is an acceleration test, but an upper limit of

60°C has to be imposed owing to the alkali-resistance properties of the fiber bond. 60°C is given as the standard immersion temperature, although any temperature in the range 20~60°C may be selected, depending on the expected application conditions and the properties of the CFRM. Temperature variation should be kept within ±2°C. (Comment on 3.3) The test piece will normally be immersed untensioned, although immersion under

tension is desirable if the material is intended for use as prestressing tendons. (Comment on 3.4) The standard immersion period shall be 1 month, variable within the range 7 days

~ 1 year. For long periods of immersion, sampling test should be carried out during the test period.

4. EXTERNAL INSPECTION Elution of the fiber bond into i nto the alkaline solution may result in changes in the surface condition, color and geometry of the CFRM, therefore a visual comparison of immersed and non-immersed specimens is required. If more detailed inspection is necessary, the polished surface or section of the test piece is to be examined under an optical or electron microscope. A physical and/or chemical analysis of the matrix may also be required.

5. MASS CHANGE The test piece is to be thoroughly washed after immersion to remove any alkali solution adhering to the surface or interior, and the hardened epoxy resin at the ends removed. The test piece is then dried to constant mass. Drying should preferably be carried out in a short time while avoiding thermal degradation, by drying in vacuum at a temperature of not more than 60°C. After leaving the test piece at normal temperature and humidity for 24 hours, the mass is to be measured to an accuracy of 0.1 g and the length to 1 mm. The mass and length of the t he test piece must of course also be measured prior to immersion.

- 157 -

COMMENTARY ON THE TEST METHOD FOR BOND STRENGTH OF CONTINUOUS FIBER REINFORCING MATERIALS BY PULL-OUT TESTING (JSCE-E 539-1995) INTRODUCTION The test method presented here is based on the JSCE "Proposed Method for Bond Testing of Continuous Fiber Reinforcing Material", published in Vol. 72 of the Concrete Library, April 1992, which was based on the draft "Pull-Out Bond Strength Testing Method" (Concrete Handbook, Japan Concrete Institute, February 1976), referencing also JSCE-G 503-1988 “Bond Strength Testing of Reinforcement and Concrete by Pull-Out (Standard Specification for Design and Construction of Concrete Structures (Standards), August 1991)” and the proposed JIS standard “Bond Strength Testing of Reinforcement and Concrete by Pull-Out”. As the standards quoted above refer to steel reinforcement, adaptations have been made to allow for the difference in materials. Revisions have also been made with reference to the draft “Long Fiber Reinforcing Material Bond Test Method” in the Long Fiber Reinforced Materials Concrete Research Report(Vol.3), March 1993”.

1. SCOPE The present test is intended for CFRM transmitting loads solely by surface bonding, and therefore excludes grid and mesh materials etc. which have different stress transmission mechanisms. In view of the outstanding processability of CFRM, however, CFRM with no fiber binding material and slab form CFRM with rectangular sections are covered by this test. There is currently no standardized test for bond performance, and in addition to the pull-out tests quoted above, other forms of test available include push-out testing, double sliding testing, beam testing etc. Each of these has merits and demerits, and so have not been established as standard test methods. The pull-out test given here has been claimed to be incapable of measuring bond strength accurately owing to the differences in the stress conditions in actual members, but it does have the advantages of being simple, executable with existing test equipment, and using test pieces of convenient size. It should be borne in mind, therefore, that the evaluation of bond performance obtained from this test is a relative evaluation.

2. DEFINITION The surfaces of CFRM are deformed in various ways to ensure bonding. Implementation of the test involves standard concepts of diameter and circumference of the CFRM, and these are therefore defined here.

- 158 -

Nominal peripheral length refers to the circumferential length when calculated from the nominal diameter, to the circumscribed peripheral length when calculated from the circumscribed circle diameter, and to the sum of the lengths of the sides where the section is rectangular.

3. TEST PIECES (Comment on 3.1) CFRM may have either circular or rectangular sections, and the surface of the

material is frequently subjected to various forms of deformation in order to improve the bonding characteristics. Section diameter therefore refers to the diameter of the equivalent circular section, and to the nominal diameter. (Comments on 3.2) The standard length of one side of the test piece shall be approximately 6 times

the diameter of the CFRM, with a bonded length 3 times the diameter and an unbonded length 2 times the diameter. This provision is to prevent yielding or rupture from occurring before pull-out when the concrete is not reinforced. The outline of the test specimen is shown in Fig. C 1.

Fig. C 1

Fig. C 2

Outline of Test Piece

Relationship between bond length & pull-out load

- 159 -

Fig. C 3

Bond characteristics for different anchored lengths

Fig. C 4

Fig. C 5

Effects of rod diameter on bond strength

Bond behavior characteristics of rod due to differences in deformation treatment

- 160 -

As the length of CFRM anchored in concrete increases, the pull-out load also increases as shown in Fig. C 2 where a more or less linear relationship is evident, but bond strength conversely tends to fall off as the anchored length increases (Fig. C 3). This can be taken to be a general phenomenon whereby the calculated apparent bond strength decreases as the anchored area increases, and this is the case also when the diameter of the CFRM increases ( Fig. C 4). Consideration has to be made here for the effects of the surface treatment of the CFRM on bond strength. It has been reported, though, as shown in Fig. C 5, that especially for stranded materials, the bond strength may be significantly affected if the anchored length is less than one pitch of the strand. In such cases, previous tests have adopted an anchored length of 30~50 cm (10 D~40 D). It has been claimed that bond strength can vary greatly due to stress disturbance within the concrete if the point of introduction of bonding into t he concrete is at the end of the test piece. For this reason, the point of introduction of bonding should preferably be inside the test piece, with an unbonded section at the loading end. (Comment on 3.3) The relationship between slippage displacement and pull-out load (bonding stress)

of the CFRM is sometimes required in connection with the bonding characteristics. For this reason, a part of the CFRM has to be left protruding from the concrete, to allow measurement of slippage displacement at the free end. In pull-out tests of steel reinforcement, the steel can be loaded mechanically by grip Cping. With CFRM, however, the use of a mechanical chuck such as that used on steel would cause a concentration of stress at that point, and could also result in rupture of the CFRM at loads far below the material strength as CFRM are generally weaker in the transverse direction than in the longitudinal direction. A gripping device to transmit loading to the CFRM at the loading end is therefore required. In practice, loading is usually carried out by connecting tie rods to the gripping device, which thus doubles as a coupler for the tie rods. (Comment on 3.4) The surface bonding strength of an undeformed circular CFRM is considerably

lower than that of steel, so the effects of concrete bleeding on bond strength are expected to be correspondingly large. In an admittedly small number of tests where CFRM cast vertically and horizontally in concrete were compared for pull-out strength, the bond strength of the horizontally cast test pieces, which are more subject to bleeding, was found to be slightly lower. In fact, however, CFRM are almost always given deformed surfaces to improve the bonding characteristics, and as Fig. C 6 shows, bond strength test results are little different from those for deformed steel bars. As the JSCE-G 503-1988 standard also specifies the horizontal position, this has been adopted here also as it gives a conservative evaluation. (Comment on 3.5) If the concrete undergoes splitting failure during a pull-out test, the bonding is lost

instantaneously and a proper evaluation of bonding characteristics cannot be made. It is therefore necessary to reinforce the concrete to prevent splitting failure before pull-out. On the other hand, this reinforcement has to be kept to a minimum, otherwise a constraining effect will appear in the concrete. Some tests of CFRM have been performed with the pitch of the reinforcing bars reduced, or with increased reinforcement, but studies of the constraining effect in these cases are still inadequate, so the original proposal has been retained here. The arrangement of reinforcement also should be gauged accurately, as it has a significant effect on the bond strength.

- 161 -

Fig. C 6

Pull-out test results for various reinforcement types

(Comment on 3.6) Three test pieces is an adequate number as the purpose of the test is to make a

relative comparison of the bonding characteristics of a CFRM.

4. FORMS The conventional type of form already in use is adopted here.

5. CONCRETE QUALITY The effects of the maximum aggregate size, slump and concrete strength on bond strength are not clear (Figs. C 7,8). The concrete quality provisions of JSCE-G 503-1988 have been retained as there is no obvious reason to change them for testing of CFRM. As CFRM are used almost exclusively in prestressed concrete, if necessary the bond strength with high strength concrete should also be tested.

Fig. C 7

Relationship of concrete strength and bond strength

- 162 -

Fig. C 8

Effects of maximum aggregate size on bond strength

6. PLACING OF CONCRETE (Comment on 6.2) The seal can consist of soft plastic tubing with an internal diameter more or less

equivalent to the maximum diameter of the CFRM, in conjunction with oil putty. The external diameter of the covered section should be in the range of 1.2~1.5 times the diameter of the CFRM.

7. REMOVAL OF FORMS AND CURING Care should be taken not to subject the CFRM to any shock.

8. TESTING MACHINE AND DEVICES The testing machine and gauge are illustrated in Fig. C 9.

Fig. C 9

Outline of testing machine

- 163 -

(Comment on 8.2) Provision is made for a hole in the loading plate to allow for the diversity of

CFRM likely to be tested. (Comment on 8.3) The gripping device also serves to anchor the CFRM. A common practice is to

place a sheath over the CFRM, filling the gap between the two with resin or expansive mortar. This is equivalent to the gripping device used in tensile test, and the test piece must not pull out before undergoing bond failure. The conditions for bond testing need not be as strict as those for tensile testing, and a gripping device similar to that used in tensile test is sufficient.

9. TEST METHOD (Comment on 9.1) The spherical plate is necessary to minimize the effects of bending and torsion on

the CFRM and the concrete.

10. CALCULATION AND EXPRESSION OF TEST RESULTS JSCE-G 503-1988 stipulates adjustment of the bond stress using the concrete strength derived by dividing the pull-out load by the bonded area. While the bond strength in cases of bond splitting are governed by the concrete strength, for other cases a good correlation with the compressive strength of the concrete has not yet been established. For this reason no corrections based on concrete strength are specified here, and the compressive strength has only to be noted in the report.

- 164 -

COMMENTARY ON THE TEST METHOD FOR SHEAR PROPERTIES OF CONTINUOUS FIBER REINFORCING MATERIAL BY DOUBLE PLANE SHEAR (JSCE-E 540-1995) INTRODUCTION Shear in CFRM is investigated in relation to lifting wire rods, or to the reinforcement effect of shear reinforcement. The former case concerns shipping or transportation, storage and stages in construction and is regarded as a construction condition. The latter case concerns shear in members, and needs to be studied in order to establish design standards. With the above in mind, the present test method is proposed as a method for determining the shear strength of materials. The test method given is simple but involves the possibility of compressive and shear deformation of test pieces. Unless test pieces are infinitely thin, the stresses causing failure are complex and do not correspond to shear in the strictest sense, but the present test is proposed nevertheless, given the current lack of a suitable alternative. “JSCE standard JSCE-G 553 1983: Shear Strength Test Method for Steel Fiber Reinforced Concrete” was referenced in drawing up this test.

1. SCOPE The test method given here is for an average shear strength of CFRM materials by shear cutting. There is currently no standard method for evaluating shear strength of wires such as CFRM, and so no standard have been set, but a method involving shear cutting of bar-shaped test pieces have been described [1,2]. The test method for shear given here, as stated in the Introduction above, cannot be said to evaluate shear strength in the strict sense owing to the complex stress situation, but the method has the advantage of simplicity and of usi ng existing test apparatus. It should therefore be noted that the test method given here evaluates average shear strength when cutting CFRM.

2. TEST PIECES Test pieces should be longer than the shear testing apparatus, not less than 5 times the distance between shear planes and not more than 30 cm. Use of bent test pieces may result in splitting of the resin or damage to the fibers themselves when the test piece is set i n the metal holders, thus test pieces must have good parallelism.

3. TESTING MACHINE AND DEVICES

- 165 -

The testing machine for shear test, illustrated in Fig. C 1, consists of a push-in cutting device and a test piece holder. The gap between the two parts must be as small as possible to enable cutting of test pieces. The surfaces contacting the test piece, illustrated in Fig. C 2, may be ( a) push-in semi-circular cutter with circular holder; (b) flat cutter with circular holder; or (c) both cutter and holder flat. A comparison using rod-shaped test pieces found that cutting strength for (b) and (c) was slightly greater than for (a). This is thought to be due to the smaller contact area between a rod-shaped test piece and a flat device, thus the test piece is cut while subject to compression. Type ( a) is thus preferred for rods, and type (c) for strips.

Fig. C 1

Fig. C 2

Double shear test machine

Combinations of test pieces and test machine contact surfaces

If the distance between the shear faces t is too large, flexing action takes place, which in some CFRM types was found to result in pull-out of fibers. Relatively uniform results for shear strength were obtained at shear face distances of 2~3 times nominal diameter although the value t = 50 mm that has been adopted here as the variation coefficient is small for different nominal diameters.

4. CALCULATION AND EXPRESSION OF TEST RESULTS The ideal test apparatus for this test would have no gap between the push-in cutter and the holder, but as this is impossible for practical purposes, the test piece is subjected not only to shear stress, but also to flexural stress and the fracture face may exhibit pull-out of fibers due to flexure as well as shear. The fracture face should be examined after testing, and if significant fiber pull-out is found, the test should be treated as invalid, and repeated after adjustment of the testing machine.

- 166 -

JSCE 1997(b)

Recommend Documents