LECTURE SERIES ON THE UPDATES OF THE NEW STRUCTURAL CODE OF THE PHILIPPINES, VOL. 1 Buildings, Towers and other Vertical Structures, 7th Edition
PART 1: CHAPTER 4, STRUCTURAL CONCRETE
3
Structural Concrete, Chapter 4 of the National Structural Code of the Philippines, Vol. I, 6 th Edition, Edition, 2010 (NSCP), was based on ACI 318 ‐08. Currently, the latest edition is ACI 318 ‐14. Prior to its publication, experts and stakeholders in the U. S. stated that the reorganization of this standard will be "monumental“, with major changes expected in the forthcoming edition. We have used the ACI 318M ‐14 as the basis for NSCP 2015 Vol. 1, Chapter 4, Structural Concrete. The first printing of NSCP Vol. 1 (C101‐ 15) was launched on Dec. 7, 2016. .
This will make the latest Chapter 4, Structural Concrete of the National Structural Code of the Philippines, Vol. I, 7 th Edition, (NSCP 2015) up to date. Our NSCP 2010 was based on ACI 318M ‐ 08, the current edition at the time of NSCP 2015 Vol. 1 inception was ACI 318M ‐11. However we have decided to use the draft version of ACI 318R ‐14 which was published in May 2014 as our guide. We have subsequently updated our final draft when ACI 318M‐14 was published in March 2015 as the basis for NSCP 2015, Chapter 4. We were able to meet our Dec. 2016 target because we have encoded the changes earlier & encoded the few corrections later.
REORGANIZATION OF NSCP 2015, 7th Edition, in accordance with ACI 318M‐14 NSCP 2015, 7th Edition, Chapter 4 Description
Section
of Provisions
and Title
Part 1: General
Part 3: Members
Remarks
Section and Title
401 – General
401 – General
402 ‐ Notation and Terminology
402 – Definitions
403 ‐ Referenced Standards
403 – Specifications for Tests and Materials
404 ‐ Structural System Requirements Part 2: Loads and Analysis
NSCP 2010, 6th Edition, Chapter 4
New
405 – Loads
410 ‐ Flexure and Axial Loads
406 ‐ Structural Analysis
408 ‐ Analysis and Design Considerations
407 ‐ One‐Way Slabs 408 ‐ Two‐Way Slabs
413 ‐ Two‐Way Slab Systems
409 – Beams 410 – Columns 411 – Walls 412 – Diaphragms 413
Foundations
414 – Walls New 415
Footings
REORGANIZATION OF NSCP 2015, 7th Edition, in accordance with ACI 318M‐14 NSCP 2010, 6th Edition, Chapter 4
NSCP 2015, 7th Edition, Chapter 4 Description of Provisions
Section and Title 414 – Plain Concrete
Part 4: Joints, Connections, Anchors
Remarks
Section and Title
Intact
422 – Structural Plain Concrete
Intact
423 – Anchorage to Concrete
Intact
421 ‐ Earthquake‐Resistant Structures
415 – Beam‐Column and Slab‐Column Joints 416 – Connections Between Members 417 – Anchoring to Concrete
Part 5: Earthquake Resistance
418 – Earthquake‐Resistant Structures
Part 6: Materials and Durability
419 – Concrete: Design and Durability Requirements
408 ‐ Analysis and Design Considerations
420 – Steel Reinforcement Properties, Durability, and Embedments
412 – Development and Splices of Reinforcement
421 – Strength Reduction Factors
426 – Alternative Load and Strength Reduction Factors
Part 7: Strength & Serviceability
422 – Sectional Strength 423 – Strength‐and‐Tie Models 424 – Serviceability Requirements
Intact
427 ‐ Strength‐and‐Tie Models 409 – Strength and Serviceability Requirements
REORGANIZATION OF NSCP 2015, 7th Edition, in accordance with ACI 318M‐14 NSCP 2010, 6th Edition, Chapter 4
NSCP 2015, 7th Edition, Chapter 4 Description of Provisions Part 8: Reinforcement Part 9: Construction
Section and Title 425 – Reinforcement Details
Section and Title 407 – Details of Reinforcements
426– Construction Documents and Inspection 427 – Strength Evaluation of Existing Structures
Part 10: Evaluation
Remarks
428 – Building Code Requirements for Concrete Thin Shells
Design
429 – Alternative Design Method
References and Appendices
Appendix A – Steel Reinforcement Information, WRI Standard Wire Reinforcement (Customary & Metric) Appendix B – Equivalence between Customary U.S. Units, SI Metric, MKS Metric
Intact
420 – Strength Evaluation of Existing Structures
Separate Publication ACI 318.2‐14
419 – Shells and Folded Plate Members
Adopted from previous NSCP Editions
424 ‐ Alternative Design Method
Appendix A
Included in Section 407 Conversion Factors (similar to Appendix B of NSCP 2015, but not yet updated to the latest ACI 318M‐14)
No longer exist as Separate sect. No longer exist as separate section
416 – Precast Concrete 418 ‐ Prestressed Concrete
Discontinued
425 ‐ Alternative Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members
Discontinued
426 – Alternative Load Strength and Reduction Factors
Chapter 4 – STRUCTURAL CONCRETE First Printing, Dec. 2016
Chapter 4 ‐ CONCRETE
401 GENERAL REQUIREMENTS 402 NOTATION AND TERMINOLOGY 403 REFERENCED STANDARDS 404 STRUCTURAL SYSTEM REQUIREMENTS 405 LOADS 406 STRUCTURAL ANALYSIS 407 ONE‐WAY SLABS 408 TWO‐WAY SLABS 409 BEAMS
Chapter 4 ‐ CONCRETE
410 COLUMNS 411 WALLS 412 DIAPHRAGMS 413 FOUNDATIONS 414 PLAIN CONCRETE 415 BEAM‐CONCRETE AND SLAB‐ COLUMN JOINTS 416 CONNECTION BETWEEN MEMBERS 417 ANCHORING T0 CONCRETE 418 EARTHQUAKE‐RESISTANT STRUCTURES
Chapter 4 ‐ CONCRETE
419 CONCRETE DESIGN AND DURABILITY REQUIREMENTS 420 STEEL REINFORCEMENT PROPERTIES, DURABILITY REQUIREMENTS 421 STRENGTH REDUCTION FACTORS 422 423 424 425 426
SECTIONAL STRENGTH STRUT‐AND‐TIE SERVICEABILITY REQUIREMENTS REINFORCEMENT DETAILS CONSTRUCTION DOCUMENTS AND INSPECTION
Chapter 4 ‐ CONCRETE
427
STRENGTH EVALUATION OF EXISTING STRUCTURES 428 BUILDING CODE REQUIREMENTS FOR CONCRETE THIN SHELLS 429 ALTERNATE DESIGN METHOD
Chapter 4 ‐ CONCRETE Although the changes from ACI 318‐08 to ACI 318‐11 are not as extensive or as substantive as those between ACI 318‐11 and ACI 318‐14, some of the changes in the latest cycle are definitely significant. To reflect the reorganization of ACI 318‐14 which contained a number of significant technical changes, the ASEP adopted similar changes in the NSCP 2015 7 th Edition. The latest ACI 318 was reorganized as a member‐based document, i. e., particular member type, such as beam, column, or slab will have separate sub‐sections for all requirements to design that particular member type. This will eliminate the need to flip through several Sections to comply with all the necessary design requirements for a particular structural member, as was necessary with the old organization format.
Chapter 4 ‐ CONCRETE Section 401 — General Requirements General information regarding the scope and applicability of NSCP 2015, Vol. 1 is provided. Additional sub‐section on interpretation is included to help users better understand Chapter 4, Structural Concrete provisions. Section 402: Section Notation and Terminology The definition for hoops has been modified because the use of interlocking headed bars is a concern regarding the possibility that it will not be adequately interlocked and because the heads could become disengaged under complex loadings well into the non‐linear range of response. It is now defined as a closed tie or continuously wound tie, made up of one or several reinforcement elements, each having seismic hooks at both ends. A definition for special seismic systems, a term used in Sections 418 and 419, has been added.
Chapter 4 ‐ CONCRETE Section 403 — Referenced Standards The following referenced specifications have been added to Section 403.2.4: ASTM A370‐14, Standard Test Methods and Definitions for Mechanical Testing of Steel Products ASTM A1085‐13, Standard Specification for Cold‐Formed Welded Carbon Steel Hollow Structural Sections (HSS) ASTM C173/C173M‐14, Standard Test Method for Air‐ Content of Freshly Mixed Concrete by Volumetric Method ASTM C1582/C1582M‐11, Standard Specification for Admixtures to Inhibit Chloride‐Induced Corrosion of Reinforcing Steel in Concrete A new referenced specification from Australia and New Zealand, Section 403.2.6 is added. These standards were included as the ACI 318 has no provisions related to Qualifications on the use
Chapter 4 ‐ CONCRETE Section 403 — Referenced Standards of Quenched Tempered QT/Thermo‐Mechanically Treated Reinforcement, which are the type manufactured, sold, and commonly used for building construction in the Philippines: 1. AS/NZS 4671: 2001, Steel Reinforcing Materials 2. NZS 3101: 2006, Part 1 and Part 2, Concrete Structures Standard, and Design of Concrete Structures 3. NZS 3109, Amendment 2, Welding of Reinforcing Steel AS/NZS 1554.3: 2008, Part 3, Structural Steel Welding of Reinforcing Steel The following referenced specifications have been deleted: 1. ASTM C109/C109M‐08, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars 2. ASTM C192/C192M‐07, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory
Chapter 4 ‐ CONCRETE Section 403 — Referenced Standards Several referenced standards and specifications have been updated, as in most cases with every edition of the NSCP. Note that the edition of every referenced standard is important. The NSCP does not necessarily adopt new editions of referenced standards unless they are vetted before the publication of each edition of the standard. Section 404 — Structural System Requirements This new Section has been added to Chapter 4 to introduce structural system requirements. This Section contains Sub‐ sections on Materials, Design Loads, Structural System and Load Paths, Structural Analysis, Strength, Serviceability, Durability, Sustainability, Structural Integrity, Fire Resistance, Requirements for Specific Types of Construction, Construction and Inspection, and Strength Evaluation of Existing Structures.
Chapter 4 ‐ CONCRETE Section 404 — Structural System Requirements Most of these Sub‐sections refer to the other Sections in the NSCP. The Sub‐section on construction and inspection, for instance, refers to Section 426. In the areas for Sustainability and Fire Resistance, the NSCP does not have specific requirements. This Sub‐section on Sustainability allows the licensed design professional to specify in the construction documents, sustainability requirements in addition to the strength, serviceability, and durability requirements of the NSCP. The strength, serviceability, and durability requirements are required to take precedence over sustainability considerations, though these requirements are generally in harmony with sustainable structures. In the Sub‐section on Fire Resistance, the NSCP refers to the fire‐protection requirements of the NSCP Chapter 4, Sub‐section 420.6.1. However, if the
Chapter 4 ‐ CONCRETE Section 404 — Structural System Requirements National Building Code of the Philippines requires a greater concrete cover, such greater thickness shall govern. Section 405 — Loads The following modification has been made in the provision for live load reduction because there are still unincorporated areas where there may not be included in the previous editions of the NSCP. The 7th Edition, Sub‐section 405.2.3 – Live load reductions shall be permitted in accordance with the National Building Code of the Philippines, or in its absence, in accordance with ASCE/SEI 7. For many Code revision cycles, ACI 318 retained provisions for service‐level earthquake forces in the design load combinations. In 1993, ASCE/SEI 7 converted earthquake forces to strength‐level forces and reduced the earthquake load factor
Chapter 4 ‐ CONCRETE to 1.0, and the model building codes followed suit. In modern building codes around the world, earthquake loads are now strength‐level forces. Therefore any references to service‐level earthquake forces (as in ACI 318‐11 Sect. 9.2.1(c) have been deleted. A requirement to include secondary moments was properly included in earlier editions of the ACI, as in the NSCP, section on moment redistribution but was not included anywhere else. Because secondary moments are significant considerations when a member is being designed, including when moments are not redistributed, they should be included in the member Sections. Also, the effects of reactions induced by prestressing include more than just secondary moments, so the language is modified to reflect this. Two new sub‐sections should be noted:
Chapter 4 ‐ CONCRETE Section 405 — Loads 405.3.11 – Required strength U shall include internal load effects due to reactions induced by prestressing with a load factor of 1.0. 407.4.1.3 – For prestressed slabs, effects of reactions induced by prestressing shall be considered in accordance with 405.3.11. Sub‐sections 408.4.1.3 and 409.4.1.3 have, similarly, been added to the Sections on Two‐way slabs and beams, respectively. Section 406 — Structural Analysis The following new item has been added in Sub‐section 406.6.2.3: (b) For frames or continuous construction, it shall be permitted to assume the intersecting member regions are rigid.
Chapter 4 ‐ CONCRETE Section 406 — Structural Analysis Previous NSCP 6th Edition has been silent on the use of finite element analysis (FEA), though it is now frequently used. Section 406 has added 406.9 with provisions that are intended to explicitly allow the use of FEA and to provide a framework for the future expansion of FEA provisions, but not as a guide toward the selection and use of FEA software. The new Sub‐ section on diaphragms and collectors makes an explicit reference to the use of FEA, which makes it imperative that NSCP 7th Edition recognize the acceptability of its use. Section 408 — Two‐Way Slabs Sub‐section 418.10.1 (corresponding to ACI 318M‐11, Section 18.9.1), says that a minimum area of bonded reinforcement shall be provided in all flexural members with unbonded prestressing tendons. The purpose of the minimum unbonded
Chapter 4 ‐ CONCRETE Section 408 — Two‐Way Slabs reinforcement over the tops of columns is to distribute cracking caused by high local flexural tensile stresses in areas of peak negative moments. However, the high local flexural tensile stresses are not unique to slabs with unbonded tendons. The new reorganized Sub‐section 408.6.2.3 (corresponding to ACI 318M‐14 Section 8.6.2.3) requires the same minimum reinforcement in slabs with unbonded or bonded tendons, except that the area of bonded tendons is considered effective in controlling cracking. It was also decided by the ACI 318 Committee, that if the same bonded reinforcement were required for both bonded and unbonded post‐tensioned two‐way systems, the structural integrity requirements for both systems should also be the same. The structural integrity requirements in ACI 318M‐11,
Chapter 4 ‐ CONCRETE Section 408 — Two‐Way Slabs Section 18.12.6 applied to two‐way post‐tensioned slab systems with unbonded tendons only. The structural integrity requirements in ACI 318M‐14 Section 8.7.5.6 (corresponding to the NSCP 2015, Sub‐section 408.7.5.6) now apply to two‐way post‐tensioned slab systems with bonded as well as unbonded tendons.
END OF PART 1: CHAPTER 4, STRUCTURAL CONCRETE
Chapter 4 ‐ CONCRETE
PART 2: CHAPTER 4, STRUCTURAL CONCRETE Section 409 — Beams The use of open web reinforcement for torsion and shear in slender spandrel beams by the precast concrete industry as an alternative to the closed stirrups traditionally mandated by this Code. Eliminating closed stirrups is desirable because they cause reinforcement congestion; production costs also increase significantly because pre‐tensioning strand must be threaded through the closed stirrups.
Chapter 4 ‐ CONCRETE Section 409 — Beams An extensive PCI‐sponsored experimental and analytical research program was conducted at North Carolina State University (NCSU). The objective was to develop a rational design procedure for slender precast concrete spandrel beams. Specifically, the research was aimed at simplifying the detailing requirements for the end regions of such beams. The end regions are often congested with heavy reinforcement cages when designed using current procedures. In addition to the experimental program, finite element models were developed (Fig. 2) and calibrated to experimental data. These models were used in conjunction with conventional analysis to corroborate the experimental results and to further investigate the behavior of slender precast concrete spandrel beams.
Chapter 4 ‐ CONCRETE Section 409 — Beams
Figure 2. Finite element model of a precast concrete spandrel beam. Image from Lucier et al., “Development of a Rational Design Methodology for Precast Concrete Slender Spandrel Beams: Part 2, Analysis and Design Guidelines” (2011).
Chapter 4 ‐ CONCRETE Section 409 — Beams A new relevant Sub‐section 409.5.4.7 for solid precast sections is added to the NSCP 2015. Section 412 — Diaphragms NSCP 2015 Sub‐section 418.12 contained design and detailing requirements, for diaphragms in structures assigned in areas of high seismicity (Zone 4). For the first time, a new Section 412, added design provisions for diaphragms in buildings assigned in areas of low seismicity (Zone 2) The new Section applies “to the design of non‐prestressed and prestressed diaphragms, including (a) through (d): (a). Diaphragms that are cast‐in‐place slabs (b). Diaphragms that comprise a cast‐in‐place topping slab on precast elements.
Chapter 4 – CONCRETE Section 412 — Diaphragms Figure 3
(c). Diaphragms that comprise precast elements with end strips formed by either a cast‐in‐place concrete topping slab or edge beams (d). Diaphragms of interconnected precast elements without cast‐in‐place concrete topping. (Fig. 3)
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures There are a number of significant and substantive changes to this Section. Column confinement ‐ The ability of the concrete core of a concrete reinforced column to sustain compressive strains tends to increase with confinement pressure. Compressive strains caused by axial load. It follows that confinement reinforcement should be increased with axial load to ensure consistent lateral deformation capacity. The dependence of the amount of required confinement on the magnitude of axial load imposed on a column has been recognized by some codes from other countries (such as CSA A23.3‐1419 and NZS 3101‐ 0620,21) but was not reflected in ACI 318 through its 2011 edition. The ability of confining steel to maintain core concrete integrity and increase deformation capacity is also related to the layout
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures of the transverse and longitudinal reinforcement. Longitudinal reinforcement that is well distributed and laterally supported around the perimeter of a column core provides more effective confinement than a cage with larger, widely spaced longitudinal bars. Confinement effectiveness is a key parameter determining the behavior of confined concrete (Mander, et al) and has been incorporated into the CSA A23.3‐14 equation for column confinement. ACI 318, through its 2011 edition, did not explicitly account for confinement effectiveness in determining the required amount of confinement. It instead assumed constant confinement effectiveness independent of how the reinforcement is distributed. In view of this, confinement requirements for columns of special moment frames (Sub‐section 418.7.5) Fig. 4) with high
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures axial load (P u > 0.3 A f c ', where P u is the factored axial force, Ag is the gross area of the concrete section; and f c ‘ is the special compressive strength of concrete) or high concrete compressive strength ( f c ' > 10,000 psi [6895 MPa]) are significantly different in ACI 318M‐14. One important new requirement for special moment frame columns is as follows: 418.7.5.2 — Transverse reinforcement shall be in accordance with (a) through (f): (f) Where P u > 0.3 A f c ‘ or f c ' > 6895 MPa in columns with rectilinear hoops, every longitudinal bar or bundle of bars around the perimeter of the column core shall have lateral support provided by the corner of a hoop or by a seismic hook, and the value of h x shall not exceed 200 mm. (Fig. 5). P u shall
Chapter 4 ‐ CONCRETE
Section 418 — Earthquake‐Resistant Structures
Figure 4. Confinement of rectangular column of special moment frame. Note: h1 = plan dimension of column in one of two orthogonal directions; h2 = plan dimension of column in other orthogonal direction; ℓo = length, measured from joint face along axis of member, over which special transverse reinforcement must be provided; s = center‐to‐ center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors. 1 in. = 25.4 mm
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures
Figure 5. Confinement of high‐strength or highly axially loaded rectangular column of special moment frame. Note: d b = nominal diameter of bar, wire, or prestressing strand; h x = maximum value of x i on all column faces greater than 200 mm.; x i = dimension from centerline to centerline of laterally supported longitudinal bars. 1 in. = 25.4 mm.
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures be the largest value in compression consistent with factored load combinations including E . where: h x = maximum center‐to‐center spacing of longitudinal bars laterally supported by corners of crossties or hoop legs around the perimeter of the column. The change from prior practice is that instead of every other longitudinal bar having to be supported by a corner of a tie or a crosstie, every longitudinal bar will have to be supported when either the axial load on a column is high or the compressive strength of the column concrete is high. The other new requirement for special moment frame columns is in the following section: 418.7.5.4 — Amount of transverse reinforcement shall be in accordance with Table 418.7.5.4 .
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures Table 418.7.5.4 Transverse Reinforcement
Conditions
Applicable Expressions
0.30g and Greater of (a) and (b)
0.3
70 MPa
g
1
(a)
0.09
for rectilinear hoop
(b)
0.30g or 70 MPa
Greatest of (a), (b), and (c)
0.2 (c)
0.30g and
Greater of (d) and (e)
0.45
g 1
70 MPa
(d)
0.12
for spiral or circular hoop
(e)
0.30g or
70 MPa
Greatest of (d), (e), and (f)
0.35 (f)
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures Table 418.7.5.4 Note: Ach = cross‐sectional area of a member measured to the outside edges of transverse reinforcement; Ag = gross area of concrete section; for a hollow section, Ag is the area of the concrete only and does not include the area of the void(s); Asb = area of longitudinal reinforcement in shear wall boundary element; bc = cross‐sectional dimension of member core measured to the outside edges of the transverse reinforcement composing area Ash ; f c ' = specified compressive strength of concrete; f yt = specified yield strength of transverse reinforcement; k f = concrete strength factor; k n = confinement effectiveness factor; P u = factored axial force, to be taken as positive for compression and negative for tension; s = center‐to‐center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors.
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures Confinement requirements for columns of special moment frames, and for columns not designated as part of the seismic‐ force‐resisting system in structures assigned to seismic zone 4 (similar to ASCE 7‐10 Seismic Design Categories D, E, and F), with high axial load or high concrete compressive strength are significantly different. Transverse reinforcement ‐ One important new requirement for special moment frame columns are included in Sub‐sections 418.7.5.2 and 418.7.5.4. There are new restrictions on the use of headed reinforcement to make up hoops. Special moment frame beam‐column joints – For beam‐column joints of special moment frames, clarification of the development length of the beam longitudinal reinforcement that is hooked, requirements for joints with headed longitudinal
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures reinforcement, and restrictions on joint aspect ratio are new. For beam‐column joints of special moment frames, clarification of development length of beam longitudinal reinforcement that is hooked, requirements for joints with headed longitudinal reinforcement, and restrictions on joint aspect ratio are new. Special shear walls – Subsection 418.10 (equivalent to ACI 318‐ 14M‐14 Section 18.10, previously ACI 318M‐11 Section 21.9), has been extensively revised in view of the performance of buildings in the Chile earthquake of 2010 and the Christchurch, New Zealand, earthquakes of 2011, as wells as full‐scale reinforced concrete building tests. In these earthquakes and laboratory tests, concrete spalling and vertical reinforcement buckling were at times observed at wall boundaries. For ASTM A615 Grade 420 bars used as longitudinal
Chapter 4 ‐ CONCRETE Section 418 — Earthquake‐Resistant Structures reinforcement in special moment frames and special shear walls, the NSCP 7 th Edition now requires the same minimum elongation as ASTM A706 reinforcement. Section 419: Concrete: Design and Durability Requirements Quite a few changes have been made in concrete durability requirements, which are now located in this Section. In previous editions (ACI 318‐11), section 5.1.5, says, “Splitting tensile strength tests shall not be used as a basis for field acceptance of concrete,” and commentary section R5.1.5 have been deleted because in the latest edition (ACI 318M‐14 section 19.2.1.2) clearly says, “The specified compressive strength shall be used for mixture proportioning in 26.4.3 (NSCP 426.4.3) and for testing and acceptance of concrete in 26.12.3 (NSCP 426.12.3).”
Chapter 4 ‐ CONCRETE Section 420: Steel Reinforcement Properties, Durability and Embedments The definition of yield strength of high‐strength reinforcement for Grade 420 (Grade 60) in this Section is now, for the first time, the same as that in ASTM specifications, except for bars with less than 420 MPa, the yield strength shall be taken as the stress corresponding to a strain of 0.35 percent. Deformed and plain stainless steel wire and welded wire conforming to ASTM A1022 is now permitted to be used as concrete reinforcement. Sub‐section 420.2.2.5 requires “Deformed non‐prestressed longitudinal reinforcement resisting earthquake moment, axial force, or both, in special moment frames, special structural walls, and all the components of special structural walls including coupling beams and wall piers” to be ASTM A706
Chapter 4 ‐ CONCRETE Section 420: Steel Reinforcement Properties, Durability and Embedments Grade 420 (Grade 60), ASTM 615 Grade 275 (Grade 40) or Grade 420 (Grade 60) reinforcement is permitted if two supplementary requirements are met, which are already part of the ASTM A706 specification. A third supplementary requirement is now added for ASTM A615 (Grade 60) reinforcement to be permitted for use in special moment frames, special structural walls. The minimum elongation in 200 mm (8”) must now be the same as that ASTM A615 (Grade 60) reinforcement. One aspect of the Code compliance that the Association of Structural Engineers of the Philippines is cautioning Designers and Constructors alike, is the introduction of ASTM 615 Grade 520 (Grade 75) in the Philippine market. Since this was not
Chapter 4 ‐ CONCRETE Section 420: Steel Reinforcement Properties, Durability and Embedments covered by previous editions of the NSCP Vol. 1, it creates an impression of an unregulated use of a new high‐strength reinforcement grade. To put it clearly, Sub‐section 420.2.2.5, corresponding to ACI 318M‐14 Section 20.2.2.5, specifies the use of deformed non‐ prestressed longitudinal reinforcement resisting earthquake‐ induced moment, axial force, or both, in special moment frames, special structural walls, and all components of special structural walls, including coupling beams, and wall piers which shall be in accordance with (a) or (b): (a). ASTM A706M, Grade 420 (b). ASTM A615M, Grade 280 There was no mention that ASTM A615M, Grade 520, was
Chapter 4 ‐ CONCRETE Section 420: Steel Reinforcement Properties, Durability and Embedments allowed, although the use of micro‐alloyed high‐strength reinforcement may be allowed in the future through the issuance of a new ASTM or updated standard, and with proper validation by the Department of Trade and Industry’s Bureau of Standards. It will be premature to allow its use for special moment frames, special structural, and all components of special structural walls, including coupling beams, and wall piers for Buildings located in areas of high seismicity (zone 4). The same restrictions indicated in Sub‐section 420.7.6, on the use of quenched‐tempered thermo‐mechanically treated (QT/TMT) reinforcing bars in structures located in seismic zone 4 for Grade 420 reinforcement, shall also be applied to Grade 520, unless proven in subsequent studies and tests.
Chapter 4 ‐ CONCRETE Section 422: Sectional Strength The following are the changes in Section 422: For prestressed members, a new equation for the nominal axial strength at zero eccentricity has been introduced in Sub‐section 422.4.2.3. New Sub‐section 422.4.3.1, which requires that the nominal axial tensile strength of a non‐prestressed, composite, or prestressed member, not to be taken greater than the maximum nominal axial tensile strength of member.
Chapter 4 ‐ CONCRETE Section 425: Reinforcement Details Two changes shown in Table 7 (part of Table 425. 3.2) are made to eliminate the differences between the required tail extension of a 90‐degree or 135‐ degree standard hook, subject to a minimum of 75 mm (3”). Mechanical or welded splices with strengths below 125% of the yield strength of the spliced reinforcing bars are no longer permitted. The associated stagger requirements have been deleted. Thus there is no longer a need to specify “full” mechanical or “full” welded splices.
Chapter 4 ‐ CONCRETE Section 426: Construction Documents and Inspection In this section, the user will probably require some time to get used to, it starts with the following: 426.1.1 This Sub‐section addresses (a) through (c): (a) Design information that the licensed design professional shall specify in the construction documents, (b) Compliance requirements that the licensed design professional shall specify in the construction documents, (c) Inspection requirements that the licensed design professional shall specify in the construction documents, Thus, construction and inspection requirements have been consolidated, and they are now related to construction documents. The construction requirements are designated either as “design information” or “compliance requirements.” These are largely existing material that has been rearranged.
Chapter 4 ‐ CONCRETE The inspection requirements in Sub‐section 426.13 are taken from Chapter 17 of the 2015 International Building Code (IBC) and were previously not part of ACI 318. Provisions in ACI 318‐11 and earlier editions, which explained basic statistical considerations in mixture proportioning, are no longer found in ACI 318‐14. Instead, ACI 301‐10, Specifications for Structural Concrete, is referenced.
Chapter 4 ‐ CONCRETE These are some other changes in the makeup of NSCP 2015 7 th Edition that should be noted: 1. There are two new Sections: Section 404, Structural System Requirements and Section 412, Diaphragms. 2. Section 422, Structural Plain Concrete, now Section 414. 3. Section 423, Anchoring to Concrete, is now Section 417, with no significant changes. 4. Section 421, Earthquake‐Resistant Structures, now Section 418. 5. Section 427, Strut‐and‐Tie Models is now Section 423, with no significant changes. 6. Section 420, Strength Evaluation of Existing Structures, is now Section 427. 7. Section 419, Shells and Folded Plates, is now Section 428. 8. 8. Section 424, Alternative Design Method, now Section 429, is adapted from earlier editions of the NSCP.
Chapter 4 ‐ CONCRETE 9. Section 425, Alternative Provisions for Reinforced and Prestressed Concrete Flexural and Compression Members, and Section 426, Alternative Load and Strength Reduction Factors, have been discontinued. 10. On the other hand, Section 416, Precast Concrete, and Section 418, Prestressed Concrete, no longer exist as separate entities. The provisions of these Sections are now spread over several of the new Sections. Sub‐section 418.18, Requirements for post‐tensioning ducts and grouting have also been removed as being outdated. The Commentary now provides specification guidance.
END OF PART 1: CHAPTER 4, STRUCTURAL CONCRETE
