Construction Method I girder

Packege 2: FRF09 Thang Long Construction Company No10

Method Statement for Production of PCI - Girders

CONTENTS 1. 2. 3.

General Locations Construction Schedule

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4.

Site Organization Chart

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5.

Materials

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6. 7.

Equipment Construction Procedure 7.1 Flow Chart 7.2 Description of Work Sequence

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8.

Quality Control

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9.

Safety Control

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10. Environmental Control

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1.


General This is a Method Statement for Production of Pre-cast Pre-stressed Concrete I-Girders (referred as “PCI girders” hereinafter) for Superstructure of Bridge Structures in accordance with Section 10 of the General Specifications. Length of PCI girders shall be fabricated to adapt with each span length in consideration with the effect of horizontal curve and change in width of carriageway. Accurate quantity will be calculated based on approved working drawing. Typical structural drawing of PCI Girders covered on this method statement is attached as.

2.

Locations Detailed and specific locations will be shown on working drawing.

3. Construction Schedule Construction Schedule shall be referred to the approved Overall Schedule. This will be revised when carry out in the site.

4.

Site Organization Chart Organization for production of PCI girders as J.O quality control Organization.

5.

Materials Materials to be used for the production of PCI girders are as follows. No. 1.

Material Reinforcing Steel Bar (Deformed Bars)

2.

Concrete

Description (General Specifications ASTM A615-

Remarks already approved

Grarde 60 S6.4) Class A-3: strength 40Mpa

already approved

(General Specifications S3.2) 3.

4.

Prestressing Steel Wire

ASTM 416-90a Grade 270

9C15

(General Specifications

(PC Tendon, Strand)

S06220_2.2.2)

Anchorage System


Cables Siam ThaiLan

Anchorage System OVM

S06220_2.2.3) 5.

PC Duct


2B80 & 2B60B

S06220_2.2.4) 6.

PC Grout


already approved

S06220_2.2.5)

Materials stocked on site shall be kept off the ground and covered properly to protect from rain and dirty.

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6.


Equipment Equipment for the production of PCI girders are shown below.

Above stated schedule of equipment shall be increased in quantity if required and necessary. Actual equipment mobilized shall be subject to inspection and approval of the Engineer

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7.


Construction Procedure 7.1 Work Flow

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7.2 Description of Work Sequence 7.2(1)

Preparatory Works

Construction of Casting Bed  Site preparation for production yard shall be carried out before mobilization of necessary materials and equipment for production of PCI girders. Location of production yard is shown on drawings. The ground surrounding the working area shall be level adequately and stable for good mobility of equipments. Access to production yard with dewatering system shall be set up adequately.  For foundation of casting bed, existing unsuitable soil such as mud or organic soil shall be replaced to suitable soil (black sand) and compacted adequately to prevent settlement of casting bed. Mobilization  Materials and equipments for the work shall be set up. And required approval such as for material testing and calibration of stressing jack and pump shall be confirmed.  Prior to commencement of works, all equipment and worker shall be inspected according to Guide Form with attendance of the Engineer.  Approval of working drawings for PCI girders shall be confirmed prior to commence production of PCI girders. 7.2(2)

Fabrication of Reinforcing Steel Bar

Details of reinforcing steel bar such as arrangement, location, dimension and shapes shall be shown on working drawings in accordance with Contract Drawings. (Reinforcing steel bar shall be referred as “rebar” hereinafter) 

Rebar shall be fabricated in accordance with the shape and dimension as shown on approved working drawing.  Material test of rebar shall be carried out in accordance with Special Specifications S10.02  Bar cutter equipment or other proper equipment shall be used for cutting rebar. Bar bending equipment or manual bending shall be used for bending rebar to form the shape and dimension as shown on working drawing.  Fabrication of rebar shall be carried out by cold cutting and cold bending. Rebar fabrication by application of heat shall be in accordance with the Engineers instruction.

7.2(3)

Setting Bottom Form

Formworks shall be in accordance with the shape, lines and dimension shown on working drawings. Forms shall be constructed to prevent deformation due to applied load. 

The length of produced girder shall be confirmed on approved working drawings. Bottom form shall be prefabricated metal form. Elevation of bottom form shall be in accordance with the designed pre-camber of PCI girders if any. Confirmation (calculation) of pre-camber will be submitted separately.  Triangular fillets not less than 25mm x 25mm to form a smooth straight chamfers shall be installed to all sharp edges of the exposed surface of bottom of PCI Girder pile cap.  All forms shall be cleaned, free from dust, grease or other foreign matter and shall be treated with 

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approved form release agent before installation.  Gap between the forms joint shall be in-filled by packing to prevent leakage of cement mortar during casting. Bottom forms shall be set in accordance to specified length of PCI girders shown on approve working drawings. Especially, end bottom forms at bearing location shall be installed having a slope to adapt to the designed grade of erected girders at bearing locations.

7.2(4)

Installation of Rebar



Rebar including embedded rebar for diaphragm shall be installed in accordance with approved working drawings.  Concrete blocks with whip shall be used as spacer. Spacer shall be installed at bottom and side of rebar in order to maintain the appropriate concrete covering. Sample of concrete spacer shall be inspected and tested for approved by the Engineer. Concrete to be used for the fabrication of concrete spacer shall be Class A. Typical arrangement of concrete spacers is shown on Figure 7.2.1.

Figure 7.2.1 Typical Arrangement of Concrete Spacers Fixing and splicing of rebar shall be done by iron wire 0.9mm or larger diameter. Splicing length and location shall be in accordance with working drawing. Ties at intersection of rebar shall be installed sufficiently to prevent dislocation during casting. Rebar shall be tied at all intersections. Fixing by welding shall only be carried out if shown on approved working drawing or as instructed by the Engineer. Installed rebar shall be free from rust, dirt, oil or other material that might reduce the bond.  Temporary embedded materials such as insert mechanical coupler for support of deck slab forms shall be installed at proper locations. Details shall be shown on working drawings. Location of temporary embedded materials shall be neatly finished with cement mortar after their role in accordance with Clause S10.01(4).1.(iii). The mortar shall be mixture of cement and fine aggregates in the same proportion as concrete Class A. Typical procedure of finishing works is shown on Figure 7.2.2.  Inspection and approval by the Engineer shall be carried out prior to setting of forms. 

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Figure 7.2.2 Typical Procedure of Finishing Surface of Concrete 7.2(5)

Installations of PC Ducts with End-Anchorage Devices



PC ducts shall be installed in accordance with designed alignment and location shown on approved working. PC duct shall be fixed and supported by temporary rebar racks and tied adequately to prevent dislocation during insertion of prestressing cable and during concrete casting  Connecting PC ducts shall be carried out with coupler and properly wrapped with vinyl tape to prevent inflow of cement past into PC ducts during casting concrete. Procedure of connecting PC ducts is shown on Figure 7.2.3.  Casting of anchorage device for stressing and bursting reinforcement (reinforcing rebar for stressing end) shall be installed in accordance with the location and arrangement shown on approved working drawing. There are 4nos. of thread holes. One is to use grouting PC duct with diameter 3/4”. Others are to use for fixing casting of anchorage device with end form with thread for diameter 8mm bolt. Casing of anchorage device shall be fixed firmly with end form by 3nos. of diameter 8mm bolt as shown on Figure 7.2.4. One hole for grouting shall be protected by plastic cap to prevent inflow obstruction.  Any obstruction shall not be allowed to be in PC duct before, during and after installation of PC ducts.

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Long PC Duct

Long PC Duct

Coupler Joint Long PC Duct

Long PC Duct

Coupler Joint Long PC Duct

Long PC Duct

Long PC Duct

Taping

Long PC Duct

Coupler Joint

Figure 7.2.3 Procedure of Connection of PC Ducts

THÔNG SỐ CHÍNH CỦA NEO CÔNG TÁC ĐẾ TRÒN OVM.M15A 9 Tấm đế neo

Ống ghen

Đầu neo

Lò xo neo

Kích căng

ØAxB

Khoảng cách lỗ định vị

ØD

ØExF

ØG

ØH

I

N

200x190

175

80

Ø146x55

Ø240

Ø14

50

5

YCW250B

Figure 7.2.4 Details at Casing of Anchorage Devices

7.2(6)

Installation of PC Strand into PC Ducts page 9…/…




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Prestressing cable shall be installed manually in accordance with the approved working drawing as shown on Figure 7.2.5. Installed Prestressing cable shall be extended minimum 60cm over both ends of girders in order to install jack for stressing. Strand shall be cut by disk cutter or other proper equipment with case to prevent damage on strand. It shall not be allowed to use fire or other heating cutting method to cut strand. Exposed prestressing cable at end of girder shall be covered by surplus PC ducts or other proper material temporary to prevent damage, dirt and rust. Cap for edge of cable will be used for easy installation and to prevent damage of PC ducts. Illustration of cap for edge of cable is shown on Figure 7.2.6. Installation of prestressing cables into PC ducts shall be taken care to prevent dislocation of alignment and damage on PC ducts. If displacement or damage of PC ducts will be happen, they shall be recovered. During and after installation of strand, it can not be allowed to apply welding work or works using fire such as gas cutting work adjacent to installed strand. They will caused defection on strand and affect to prestressing. PC DUCT PC STRAND

COIL OF PC STRAND

WORKING PLATFORM

BASE SUPPORT

PCI GIRDER

Figure 7.2.5 Installation of Prestressing Cables  Location, alignment and condition of PC ducts and casting of anchorage devices shall be inspected by the Engineer in accordance with approved working drawing at each 1.0m interval of girder length and at the point of changing alignment of prestressing cable. Allowable displacement of Pc ducts and anchorage devices are within +5mm of design for horizontal and vertical.

Figure 7.2.6 Cap for Edge of Cable for Installation

7.2(7)    

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Installation of Side Form Pre-fabricated metal form panels shall be used for side forms. Layout of forms shall be installed in accordance with design of forms cased on approved working drawings. Temporary support shall be installed properly in accordance with design of form. All forms shall be cleaned, free from dust, grease or other foreign matter and shall be treated with the approved form-release-agent before installation Triangular fillets not less than 25mm x 25mm to form smooth straight chamfers shall be applied to page 10…/


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PCI - Girders

all sharp edges of the exposed surface of PCI Girder. Holes on side form for embedded rebar for diaphragm shall be made at proper location with proper dimension. Clearance around embedded rebar on forms shall be closed by cotton waste or other proper material to prevent leakage of cement past during casting concrete as far as possible. Block out of lifting holes (2nos. of dia.60mm) at end of girder shall be set before closure of forms with reinforcement for lifting holes. Typical drawing of lifting holes is shown on Figure 7.2.7. Details shall be shown on working drawings for the approval of the Engineer. The location of lifting holes is within end diaphragm. And they will be filled concrete with casting concrete of diaphragm. Gap at joints of forms shall be in-filled by packing to prevent leakage of cement past of casting concrete. The gap between metal form and supporting beam shall be also in-filled by suitable material such as cleat to prevent displacement of forms. Before closure of forms, inside of forms shall be cleaned properly. If cleaning inside form is unsatisfactory for acceptance under inspection of the Engineer after closure of forms and before casting of concrete, some of form will be opened and cleaning shall be carried out again for acceptance. After completion of installation of forms, inspection shall be held in attendance with the Engineer for approval to cast concrete.

7.2(8) 

Method Statement for Production of

Casting Concrete

Crane and concrete bucket will be used for casting concrete of PCI girders. Water shall be sprayed on form, rebar and surface of bottom form prior to concrete casting. Casting shall be carried out layer by layer of approximately 50cm and casting concrete shall be proceeded from one end going to the opposite end. The vibrators shall be of type with proper frequency and shall be capable of visibly affecting a properly designed concrete with a 2cm slump over a circular area of 45cm radius. The number of vibrators shall be sufficient to consolidate the concrete properly within 10 minutes after it is deposited in the forms. At least 3 spare vibrators shall be available on standby at site to maintain immediate continuity in case of breakdown. Static vibrator (external vibrator) will be set on outside forms Vibrator shall be penetrated into the previously cast layer through the new casting layer. Operation of vibrator shall be taken care not to damage PC ducts. And especially anchorage location at end of girder shall be taken care to compact concrete strictly to prevent any defect of concrete because this portion will not be allowed to apply any remedial and repair of concrete. The top of 1st layer shall be on top of hunch of bottom flange of girder. And compaction shall be taken care strictly to prevent air void on surface of concrete of hunch. Firstly, flexible vibrators shall be used to compact concrete for each layer. And secondary, static vibrators on side forms shall be operated proper duration for 1st ~ 3rd layer. The top of 2nd layer will be on middle of web of girder. Static vibrator will be operated to compact concrete after compaction by flexible vibrators same as for 1st layer. Concrete vibrators will not be used to transport concrete inside the formwork during casting. Concrete condition shall be closely monitored to avoid concrete to harden before casting the next layer. The new concrete shall be placed within maximum 2 hours after placing the previous below contact layer. Splattered and loose concrete on surface of form shall be removed before placing concrete. Tightness of the formworks shall be inspected and monitored regularly during casting to prevent deformation or displacement of forms and leaks at the formworks. In case displacement occurs, they shall be immediate adjusted to before concrete placing continues. page 11…/

Packege 2: FRF09 Thang Long Construction Company No10  

 

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Installed rebar shall be taken with care to prevent dislocation during casting concrete. In case dislocation occurs, they shall be immediate adjusted to before concrete placing continues. Installed PC ducts with PC cable shall be taken with care to prevent dislocation during casting concrete. In case dislocation and damage occurs, they shall be immediate adjusted to before concrete placing continues. Casting speed shall be monitored not to exceed the designed pressure considered on the design of formwork. After placing concrete, splattered concrete on rebar shear connectors shall be cleaned. Concrete surface shall be hand finished using steel trowel at least 2 times including the final finishing. Tolerance in casting height shall be ±20mm. In-situ testing for concrete shall be carried out per each delivery truck in accordance with approved Inspection and Test Plan. Sample of concrete shall be taken to make specimen for compressive testing in accordance with approved Inspection and Test Plan (ITP) in accordance with General Specifications S10.01. In order to confirm concrete strength at the time of prestressing, specimen shall be made additionally minimum 3sets for compressive testing (9 specimens). These specimens for confirmation of strength for prestressing shall be cured at site under same condition of concrete of casting PCI girders.

In case of emergency and it is necessary to stop placing concrete before a section is completed, following measure shall be taken. In case of rainfall, pooling water shall be removed on the surface of concrete before making the surface level. And plastic vinyl sheet shall be installed covering all areas of concreting. In emergency case due to crane or bucket breakdown, broken crane or bucket shall be replaced with standby one. However, it is subject to rejection of girder which has such construction joint with inspection and evaluation by the Engineer. Detailed report on nonconformance shall be made if such emergency case will be occurred.

7.2(9)     



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Curing and Removal of Side Forms

Exposed surface of girder (top surface of girder) shall be covered by wet burlaps or other suitable fabric material immediately after final finishing of concrete surface. After one day of casting concrete, side forms shall be dismantled. And girders shall be covered by wet burlaps or other suitable material immediately For winter season, steam curing method will be applied in accordance with General Specifications S10.03(3)(d) in order to reduce time to obtain required strength of concrete for prestressing Removal of forms shall be taken care not to damage or injure concrete surface and embedded rebar of girder. In case that the girders will be stocked for a long time after casting, surface of embedded exposed rebar such as for diaphragm and deck slab shall be covered by cement paste to prevent corrosion and rust. After removal of forms, surface of concrete where diaphragm will be constructed shall be treated with chipping as construction joint.

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Figure 7.2.9(1) Curing of PCI Girders-1

Figure 7.2.9(2) Curing of PCI Girders-2

7.2(10)

Stressing PC Tendon

General sequence of prestressing work is shown on Figure 7.2.10.

Figure 7.2.10 General Sequence of Prestressing Work

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I.


Preparatory Work 

Prior to commencement of works, all equipment and worker shall be inspected according to Guide Form approval with attendance of the Engineer. 

Calibration of prestressing jack and pump shall be carried out by approved authorized laboratory (IBST) with attendance of the Engineer. 

Certificate of above calibration shall be reported to the Engineer for approval, which shall show the relation of reading manometer and actual applied force by jack. Combination of jack and pump shall be clarified.

II.

Test Prestressing Stressing will be controlled with friction coefficient of PC strand. Necessary parameters for control stressing are friction coefficient (μ’) and apparent Young's modulus (E’p) of strand. In order to obtain friction coefficient and apparent Young's modulus of strand, test prestressing will be carried out on 1st produced girder. And test pressing will be applied to all (5nos.) cables on girder. Sequence of test prestressing is shown as below. (1)

Setting End-Anchor Blocks and Jacks End-anchorage shall be set without wedges. And jacks shall be set at both end of girder. One side of jack (Jack A) is operated for prestressing. Another side of jack (Jack B) is not operated and fixed, which hydraulic valve shall be closed. Before prestressing, some stroke of Jack B shall be provided to remove jack easily after prestressing. Name of jack is referred to Figure 7.2.11.

(2)

Initial Prestressing Prestressing force is provided up to 5MPa (50Bar) of pressure on Jack A. Marking to measure elongation shall be given on prestressing cable at end of Jack A. And marking to measure pull-in shall be given on prestressing cable at end of Jack B.

Figure 7.2.11 Setting Jacks for Test Prestressing (3)

Prestressing Prestressing is continued step by step with interval 5MPa (50Bar) of pressure on Jack A up to final pressure During each step of prestressing up to final, reading manometer on Jack A and Jack B and elongation at Jack A and pull-in at Jack B shall be recorded After final pressure is applied, Jack A shall be released pressure. (4) Reverse Prestressing On the same strand, prestressing shall be applied with condition that Jack A is fixed and Jack B is jacking. Sequence of prestressing is same as shown above (1) ~ (3).

(5)

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Continue Sequence (1) ~ (4) on Other Cables After prestressing on 1st cable, test prestressing shall be applied other cables with same sequence page 14…/



of (1) ~ (4) Friction coefficient (μ’) and apparent Young's modulus (E’ p) of strand will be calculated based on the record of test prestressing on 1st girder. Report shall be submitted with calculation result of friction coefficient and Young’s modulus of strand which shall be used for control of permanent prestressing. The materials and girder which is applied to test prestressing shall be used for permanent prestressing.

III. Provision of Prestressing Control Chart Prestressing Control Chart shall be provided with friction coefficient (μ’) and apparent Young’s modulus (E’p) which are determined by test prestressing. Prestressing Control Chart shall be submitted to the Engineer for the approval before commencement of prestressing.

IV. Permanent Prestressing on PCI Girders Sequence of permanent prestressing work is shown on Figure 7.2.12.

Figure 7.2.12 Sequence of Prestressing Work Prior to commencement prestressing, concrete strength shall be confirmed more than 90% of designed strength of average of three compressive testing results with testing specimen cured on site under same condition of girders. …

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Description of each sequence of prestressing work is as follows. (1) Removal of Bottom Forms at Bearing Bottom forms at bearing location of girders shall be removed and replace to rubber pat in order to follow suit for deflection (camber) of girder during prestressing.

Figure 7.2.13 Setting Rubber Pat at Bearing Location

(2)

Setting End-Anchor Blocks with Wedges Surface of casting of anchorage shall be clean from laitance of concrete to prevent the occurrence of gap between the casting and end-anchor block prior setting End-Anchor Block.  End-anchor block shall be installed with wedges as shown Figure 7.2.14. Prior to install anchor blocks and wedges, lubricating grease will be applied on external face of wedges or surface of wedging hole on anchor blocks in order to ensure to draw in wedges properly during prestressing. 

Figure 7.2.14 Setting End-Anchor Block

(3)  

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Setting Jack and Pumps for Prestressing Approved combination of stressing pump and jack shall only be used in carrying out prestressing. Prestressing Jack shall be installed at both end of anchor location of girder. Jacks shall be installed properly without decentering on axis of prestressing cables in order to prevent non-uniform stressing on one tendon. page 16…/





Installation of jack shall be carried out using crane or chain block attached to a frame. Jacks shall keep proper location with hanging prior to commencement of prestressing.  After setting jacks, hydraulic pump shall be connected to jacks with confirmation of approved combination.  Required actual reading manometer for each step of prestressing in accordance with calibration result of jack and pump shall be summarized on table and shown at site.  Persons who in charge prestressing works shall be arranged as shown on Figure 7.2.15. N

Person

Description of Role

Nos. of person

o. 1. 2.

Chief Site Engineer (Contractor)

Control Prestressing

Site Engineer (Contractor)

1 person

Making Control Chart

1 person

3.

Operator (Subcontractor)

Operation Pump

2 persons

4.

Skilled Worker (Subcontractor)

Checking Elongation

2 persons

5.

Skilled Worker (Subcontractor)

for General work

2 persons

1 2 PC STRANDS

1

PC STRANDS J ACK

J ACK

3 CONTROL PUMP

1 2

2

3 PCI GIRDER

PCI GIRDER

CONTROL PUMP

Figure 7.2.15 Arrangement of persons in charge 

Protection board shall be set behind jack for safety. And notice to keep off behind jack during prestressing shall be got across all relative persons working on site. (4) Applying Prestressing on Each PC Cable Sequence of prestressing on each type of girder is shown on Figure 7.2.16.

C1

C2

C3

Figure 7.2.16 Sequence of Prestressing

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Work sequence of each prestressing is described as follows. (4-i)

Initial Prestressing



Prestressing shall be applied by both jacks. 

Initial prestressing shall be applied up to 5MPa (50Bar) on reading manometer to remove fudge factor of tendon as far as possible. And release pressure to 0 again. 

Marking by splay color shall be provided on PC cables at end of anchor block in order check visually slipping strand in jack during prestressing or slipping wedging strand after prestressing. 

And prestressing shall be applied up to 5MPa (50Bar) again and marking on strands shall be provided in order to measure elongation during prestressing as shown Figure 7.2.17. 

Contacting condition between anchor block and casting surface and between surface of jack and anchor block shall be checked. 

If there are some gaps for the above checking or decentering of jack on axis of PC cables visually, pressure on jack shall be released to 0 again and initial prestressing shall be applied again with 5MPa pressure of jack on manometer.

(4-ii)

Figure 7.2.17 Marking on strand to measure elongation Prestressing up to Final



Prestressing shall be carried out step by step with interval 5MPa (50Bar) on reading manometer as shown Figure 7.2.18. 

Elongation shall be measured at each step and plotted on Prestressing Control Chart as shown on Figure 7.2.19. 

When prestressing force is achieved to approximately 75% of final prestressing force, make line (measuring line) on plotting point on Prestressing Control Chart and this line is moved …

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in parallel through original point (control line). Intersection of control line and stop line for prestressing is the point to stop prestressing as shown on Figure 7.2.19. 

After making control line, it shall be confirmed whether the line is within control limit on Prestressing Control Chart. 

Prestressing shall be proceeded up to final prestressing force. 

Actual friction coefficient shall be read on Prestressing Control Chart and recorded. It shall be taken on intersection of E’p-line and control line.

Mesure Elongation

. .L C L.

Stop Line

Absolute Upper Limit

.C

.L

.

Final Prestressing Force

U

U

.C

.L

.

Absolute Upper Limit

Reading Manometer (Bar)

Reading Manometer (Bar)

Figure 7.2.18 Jacking and Measuring Elongation

. .L C L.

Control Line (move in parallel mesuring line)

Measuring Line 0

Stop Line

Measuring Line 0

Elongation (mm) 1. Measure and Plotting Elongation at each step

Elongation (mm) 2. Making Control Line and Determination of Final Prestressing Force

Figure 7.2.19 Prestressing Control 

If the control line is not within control limit on Prestressing Control Chart, prestressing shall be stopped. And condition of jack and strand shall be checked. Finally, nonconformance report will be made. And countermeasure to recover shall be proposed. 

Prestressing can not be allowed to apply more than absolute upper limit of prestressing.

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(4-iii)


Release Pressure and Removal of Jack



After measure elongation at final prestressing force, pressure on jacks shall be released up to 5MPa (50Bar). And pull-in shall be measured and calculated in consideration of residual elongation of PC cable in jacks under pressure of 5MPa on manometer. 

It shall be confirmed that actual pull-in is less than allowable pull-in. 

After measuring pull-in, pressure on jacks shall be release all. And jacks shall be removed. (5)

Shift to Next Prestressing Cable Jack shall be set on next PC cable and continue same sequence of prestressing as above mentioned.

(6)

Group Control After completion of prestressing on each girder, data on each prestressing control chart shall be summarized on group control graph with parameter μ’. One group will be made per girder. Limit of group control will be set as follows.

Upper Limit of Control: μ’+ a Lower Limit of Control: μ’- a where, tolerance “a” will be taken from Table 7.2.2. Table 7.2.2 Tolerance for group control

Group control is to evaluate condition of prestressing with parameter μ’, which is based on standard deviation (σ) of μ’ - (2σ method) to prevent defect on each prestressing. It shall not be considered as defect on each girder of prestressing even though over limit is occurred on group control. Therefore, Evaluation of prestressing on group control is provided as follows. 

It is normal in case that all points on graph are within limit adequately. 

It is not determined as defect if over limit is occurred at the rate of less than 1/20 because probability of over control limit on group control is considered 1/20 on 2σ method. 

If over limit is occurred at the rate of more than 1/20, it is necessary to investigate causes on operation of prestressing, procedure of prestressing, equipments or others. 

If more than 5 points are plotted at one side continuously (lower or upper side of center line) on graph, it is necessary to investigate causes and take countermeasure to recover condition. 

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If more than 7 plotting points on graph are continuously rising or coming down, it is necessary to investigate causes and take countermeasure to recover condition. The control limit of prestressing for each prestressing and group will be reviewed and revised in consideration of standard variation of actual measured friction coefficient μ’ after approximately 20 nos. of prestressing, if result of test prestressing is considered as not representative data for actual prestressing. Prestressing Control Chart and Group Control shall be submitted to the Engineer as soon as possible after prestressing each girder for approval. (7) Measure the camber of girder 

Preparation 

Using tapes applied at 5 locations: 0; 1/4L; 1/2L. 

Using theodolite with accuracy 2mm/1000m for measuring the camber. Following the transversal deplacement of center line along girder

(8) 

For preparation stage, determine the longitudinal centerline of girder and mark 3 locations:two leght and right side, and centerline. Fix the theodolite for examination. 

Through the tensioning process, after finish each tendon, examine the transversal deplacement at 3 locations. (9)

Cutting Strand at End of Anchorage



Strand shall be cut after approval of prestressing result by the Engineer. Strand after cutting shall be at least 3cm from the face of Anchor head as shown on Figure 7.2.20. 

Cutting of strand shall be carried out by disk cutter.

Anchor Block

approx. 3cm

PC Cable

Figure 7.2.20 Cutting Strand after Prestressing

7.2(11) Side Shifting Girder to Stock After prestressing is completed, PCI girders shall be shifted to stock from casting bed. The sequence of shifting is as follows. …

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Step1: Installation of Lifting Box at lifting hole of PCI girder Set up two hydraulic Jacks at both sides at first one end of girder for jacking up Details of Lifting Box are shown on Appendix-8

Step2: Lift up PCI girder approx. 200mm above concrete base by two jacks at one end. Jack up shall be carried one by one end of PCI girder to set trolley cart.

Step3: Place trolley cart under girder Release jacking slowly down to set bottom of girder on trolley cart Remove hydraulic jacks Install diagonal support on trolley cart for supporting PCI girder Above procedure shall be proceeded at one by one end of PCI girder Setting channel bar (C-200×50) for rail of trolley cart

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Step4: Installation of pulling cable to trolley cart Start shifting PCI girder up to the location to be stocked slowly with pulling trolley cart by mechanical winch or other equipments

Step5: Stop shifting at the location to stock

Step6: Set up two Hydraulic Jacks at both sides of PCI girder at one end first Installation of movable sleeper support at bottom of PCI girder

Step7:

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Lift up Pci girder to just enough height in order to remove trolley cart

Step8: Remove trolley cart from bottom of girder Confirm the setting location of movable sleeper Release jacking slowly so that PCI girder set on sleeper support

Step9: Remove Hydraulic Jacks and Lifting Box Install temporary diagonal support (above sequence Step6 to Step10 shall be proceeded one by one end of girder)

High attention shall be paid during jacking to check equal stroke at both side of PCI girder and to check stability of lifting box and PCI girder. Any person shall not allow to stay side of PCI girder. Pulling trolley shall be slowly with same speed at both end of girder. After shifting is completed, stability of PCI girder and condition of temporary support shall be checked strictly. 7.2(12) Treatment of End of PCI Girders

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Packege 2: FRF09 Thang Long Construction Company No10    




Packing of block out for anchorage location of prestressing shall be carried out by casting concrete prior to grouting PC ducts. The surface of end of PCI girder to be contacted with casting concrete shall be treated with chipping as construction joint. Condition of anchorage such as anchor brocks, strand and wedges shall be checked finally. If dirty or rust is found, they shall be cleaned. Prior setting form at end of PCI girder, grout hose with adapter socket of PVC pipe shall be installed properly as shown on Figure 7.2.21. PVC adapter socket with screw shall be inserted to thread hole (dia.3/4”) on casting of anchorage devise. And 90 o elbow of PVC pipe shall be connected with adapter socket to make vertical to install grout hose. Grout hose shall be connected with PVC pipe firmly with iron wire. Grout hose shall be fixed with embedded rebar at top of PCI girder to keep straight and to prevent stuck due to bending.

THREADED HOLE ON CASTING (3/4") g r o u t in g h o s e (d ia.25mm)

PVC Pipe (adapt e s o c ket +El bo w ) Cas t ing o f An c ho r ag e

pc d uc t

Figure 7.2.21 Connection of Grout Hose with Anchorage Device   

Form at end of girder shall be set properly as shown on Figure 7.2.22. Concrete to be cast shall be same proportion of PCI girder (Class A-3). Concrete shall be cast with concrete bucket and chute. Concrete shall be compacted with mechanical vibrator adequately with care to prevent damage on grout hose and bending grout hose.

Figure 7.2.22 Connection of Grout Hose with Anchorage Device  

…

Before concrete, make the girder-end rugged. Its geometric dimensions should be assured in accordance with design



Don’t weld reinforcement for concealing girder end to anchor and high strength cable



Curing is carried out as curing girder concrete page 25…/


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7.2(13)


Grouting PC Ducts

Sequence of grouting PC ducts is shown on Figure 7.2.23.

Figure 7.2.23 Sequence of Grouting PC Ducts The description of each sequence of work is as follows. 1. Preparation Work  Prior to commencement of grouting works, inspection of mobilization of equipment and labor shall be taken for the approval of the Engineer.  Grouting PC ducts (PC grout) shall be in accordance with Clause S10.03. Materials and proportion of grout is proposed separately  Equipments such as grout mixer and pump shall be set as shown on Figure 7.2.23.  Grout hose shall be set (connected) with pre-installed hose in girders firmly. 2. Check Ventilation and Cleaning PC Ducts  Air hose from air compressor will be connected with one side of grout hose. And air will be provided into PC ducts. Ventilation of PC ducts shall be checked by air at another side of grout hose.  At same time, excess water or other foreign material shall be blown out.  If ventilation can not be confirmed, duct has stuck. In such case, location and condition of stuck shall be investigated and countermeasure to recover shall be proposed.

3. Mixing Grout  Actual mixing per batch shall conform to the approved mix proportion.  Mixing procedure shall be as follows. 1. Water + Sikament R4 → 2. Cement → 3. Intraplast Z → (mixing 4minutes) …

page 27…/

Packege 2: FRF09 Thang Long Construction Company No10  


After mixing is completed, grout shall pass through a screen with 1.2mm maximum clear openings prior to being introduced into the grout pump. After mixing soon, in-situ testing shown on Table 7.2.3 shall be carried out. Table 7.2.3 In-situ Testing for PC grout No

Item

Uni

Criteria

Test Method

t 1.

Flow time

sec

> 13.0

2.

Temperature

o

less than 35oC

3.

Compressive Strength

MP

more than 32MPa at

ASTM C939

< 25.0

(making specimen)

C

a

28days

TCN247-98 *

Minimum 6nos. of specimens (70×70×70mm) per PCI girder shall be produced. (3nos. of specimens per testing for 7days and 28days compressive strength)

 

All grout shall pass through a screen with 1.20mm maximum clear opening prior to being introduced into the grout pump. Grout shall be used within 30minutes after mixing of each batch to ensure flowability and expansion of grout.

4. Injection of Grout  All grout vents shall be opened.  Grout hose of pump shall be connected with one side of grout vent of PCI girder.  Arrange person in charge of grouting as shown on Figure 7.2.23 shall be confirmed.  Grout shall be pumped through the duct and flow continuously at first outlet after inlet, until no visible slugs of water or air are ejected and the consistency of grout is equivalent to that of grout injected, at which time the outlet shall be closed.  Pumping pressure at inlet shall not exceed 1.0 MPa.  After closure of outlet, pressure 0.5 MPa shall be maintained for one minute.  After one minute with pressure, inlet pumping pressure will be released and condition of grout at inlet hose shall be confirmed whether grout has back flow or reducing.  After above, pressure shall be provided up to 0.5 MPa again. And inlet shall be closed. (pressure 0.5MPa → release → pressure 0.5MPa → closure of inlet)  Closure of outlet and inlet will be carried out by the measure of clinch and binding of grout hose.  After completion of injection, grout hose shall be maintained vertical as shown on Figure 7.2.24. The excess length of grout hose exposed above concrete shall be more than 1m for one day.  In case that injection is interrupted due to machinery trouble or other reasons before completion, all grout injected in duct shall be flushed out of duct with water by water pump or other proper equipment immediately. Figure 7.2.23 PC Grouting Work

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page 28…/


Outlet Grouting Hose


Inlet Grouting Hose

Grouting Mixer and Pump Operator Valve

Figure 7.2.24 Treatment Grout Hose after Grouting 5. Cutting Grout Hose  After one day of grouting, breathing shall be checked visually in exposed grout hoses.  If breathing is found in grout hoses, it shall be within exposed grout hoses (above concrete of PCI girder) for acceptance of PC grouting.  After confirmation of breathing, excess grout hoses shall be cut on surface of concrete of PCI girder.  Girder shall not be moved within 48hours after grouting.

8.

Quality Control The whole procedure shall be thoroughly checked by the engineer in charge for operation. Quality control shall be carried out in accordance with this Method Statement and other applicable Specifications.

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page 29…/



Inspection Checklists are subject to revision in accordance with the Engineer’s instruction. Each PCI girder shall be uniquely and permanently marked so as to show name of girder (no. of girder) and casting date. Tolerance for Concrete Structures In general, Tolerance for Concrete Structures shall be in accordance to Clause SS.10 of the Special Specifications. However, it is subject to change following the Instruction by the Engineer. The following tolerance of concrete structures after completion of the work shall not be exceeded. 1) Dimensions of section of girders 2) Concrete Cover and Space for Reinforcing Steel a. Concrete Cover for Superstructure b. Space for Reinforcing Steel 3) Position for Pre-stressing Tendons a. Horizontal and Vertical

±8mm ±5mm ±10mm ±5mm

The product length and pre-camber of girder shall be proposed separately.

9.

Safety Control Method Statementand shall be part of this Method Statement. Prior to starting of substructure works, the following particular matters are to be through to all members working in the construction site in order to complete the substructure work efficiently without any accident or casualty. 9.1 Joint Meeting Prior to start any activity, a joint meeting with relevant staffs shall be held for the purpose of general explanation on the whole contents of works as well as the method for the implementation of efficient work. 9.2 Basic Instruction All workers shall wear Personal Protective Equipment (PPE) at all times, such as hardhat (helmet), safety shoes, hand gloves and working uniform. 9.3 Prevention accident during Stressing Workers shall not be allowed to stay at the backside of stressing jack during stressing and measuring. 9.4 Prevention accident during Grouting Coordination shall be carried out especially when closing grout hose to prevent bursting due to applied pressure. 9.5 Prevention of Accident by Heavy Machine

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Only skilled operator shall be allowed to operate equipment on site. In case of new operators, a test of skill shall be conducted first prior to his acceptance to the job. Preventive maintenance check shall be done regularly at equipment working at site prior to full operation. Stability of working area and foundation of equipment shall be checked particularly at locations of outrigger and track pad of cranes. 9.6 Prevention of Accident of Electrocution Electric generating equipment shall be properly protected and properly installed with earth connection. Electric wires shall be connected with electrical tapes to prevent electric leakage. Only skilled operator shall be allowed to operate equipment on site. 9.7 Prevention of Accident in Night Shift Works Sufficient quantity of lighting system shall be provided for night shift works especially installed at working platforms. If necessary all of the surrounding working area shall be lighted up. 9.8 Existing Facilities Existing facilities especially existing overhead electric line, water line, telecommunication line and other important facilities at surrounding area shall be taken with care not to damage.

10. Environmental Control Responsibility for surrounding environment during Substructure work and shall comply with the Condition of Contract and Vietnam’s National Law on Protection of Environment and other relevant legislation such as: Government Decree No.175/CP, Government Decree on providing Guidance for the Implementation of the Law on Environmental Protection, 1994. If any other problems occurred in the site, applicable counter measures or prevention action shall be considered immediately and executed as soon as possible.

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Construction Method I girder

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