07 3 iok a1 SUPERSTRUCTURE

Table reference standards:  22TCN 272-05 Specification Standard for Bridge Design  22TCN 247-98 Specification for Construction and Acceptance ofPrestressed Girder  TCVN 9114:2010 Prec

II CASTING YARD AND FORMWORK

III CONCRETE WORKS

IV TENSIONING PRESTRESSING STEEL

V QUALITY ASSESSMENT AND INSPECTION OF I BEAM

VI CONSTRUCTION OF I33M BEAM

VII CONSTRUCTION OF I24, I40M BEAMS

VIII CONSTRUCTION OF PC VOID SLAB GIRDER - CASTING ON SCAFFOLDING

CHAPTER II: INSTALLATION OF I BEAMS

I CONSTRUCTION REQUIREMENTS

II INSPECTION OF QUALITY

III THE SEQUENCE CONSTRUCTION OF THE SUPERSTRUCTURE FOR EACH BRIDGE

CHAPTER III: CONSTRUCTION METHOD OF OTHER WORK ITEMS

I BEARINGS

II CONSTRUCTION OF CROSS BEAMS

III CONSTRUCTION OF PARAPET

IV CONSTRUCTION OF EXPANSION JOINTS

V BRIDGE DECK WATERPROOFING MEMBRANE

VII CONSTRUCTION OF BRIDGE DRAINAGE

NGAI SECTION

CHAPTER I: CONSTRUCTION TECHNOLOGY OF PRESTRESSED RC BEAM

All works of this items must be complied with “SPECIFICATION SECTION

07400 - PRESTRESSED CONCRETE AND PRESTRESSING”

The contractor will provide skilled technicians in the construction ofprestressed structures, monitoring work and supporting the Engineer ifneeded

The Contractor shall provide all types of machinery and equipmentnecessary for construction and pre-stressed tensioning Prestressedtensioning must be carried out by appropriate jacking equipment system,which has been approved If hydraulic jacks are used they shall be equippedwith accurate pressure gauges The combination of jack and gauge shall becalibrated and a graph or table showing the calibration shall be provided tothe Engineer

Table reference standards:

 22TCN 272-05 Specification Standard for Bridge Design

 22TCN 247-98 Specification for Construction and Acceptance ofPrestressed Girder

 TCVN 9114:2010 Precast Prestressed Concrete Products - TechnicalRequirements and Acceptance

 22TCN 267-2000: Anchor for Prestressed Concrete T13; T15 & D13; D15

International Standard:

 ASTMA416M Steel Strand, Un-coated Seven Wire Stress Relieved

 Grade270 Strand for Pre-stressed Concrete

 AASHTO M235 Epoxy Resin Adhesives

2. Material Requirements

2.1 Prestressing Steel

Reinforcement must comply with article 2.2.2 “Reinforcing Steel” of

“Specification section 07400 - Prestressed Concrete and Prestressing”

High tensile steel strand with low relaxation shall be weld free and stressrelieved after stranding and shall conform to the requirements of ASTMA416M-Grade 270 or equivalent steel strand, uncoated seven wire stressrelieved strand for Prestressed Concrete

All post tensioned prestressing steel shall be secured at the ends by means

of approved permanent type anchoring devices The Contractor shall submitinformation and details, including test certifications for by the Engineer.End anchorage devices (stress and dead anchors) shall be designed andmanufactured for the types of tendons to be used They shall have aprevious service record of performance and durability when used on similartype work

All anchorage devices for post tensioning shall be capable of holding theprestressing steel at a load of not less than 95 percent of the guaranteedminimum tensile strength of the prestressing steel

It is the responsibility of the Contractor to design reinforcement, which takescognisance of the bursting force produced by the particular shape anddesign of the anchorages

All exposed steel parts shall be protected from corrosion All threaded partsand fittings shall be protected by greased wrappings or plugs until used.Anchorages shall be kept free from dirt, mortar, loose rust or otherdeleterious materials Damaged anchorage parts shall not be used

2.3 Ducts for internal Tendons

Ducting for internal tendons shall be fully compatible with the proposedprestressing system Ducting for internal tendons shall be fully compatiblewith the proposed prestressing system The ducts shall be fabricated fromcorrugated galvanized sheet steel or semi rigid conduit

Minimum duct thickness shall be as follows:

 0.45mm for duct diameter less than or equal to 67 mm

 0.6mm for duct diameter greater than 67 mm

 0.25mm for bar tendons

Ducts shall have grouting connections at each end and shall havevent/drains at all intermediate high and low points, subject to the approval

of the Engineer

2.4 Grout for Ducts

Unless otherwise specified in other prevailing Specification Sections orsubject to approval by the Engineer as a result of grouting trials the groutshall:

 Consist only of ordinary Portland cement (PC40,PC50 with chlorideand sulphate contents of less than 0.5%) water and expansiveadmixtures approved by the Engineer and used in accordance withthe manufacturer’s instructions,

NGAI SECTION

 Have a water to cement ratio as low as possible consistent with thenecessary workability, and under no circumstances shall thewater/cement ratio 0.34 - 0.38 (without admixture < 0.4; withadmixture < 0.38)

 Contain no admixtures containing chlorides, nitrates or similarelectrolytic conducting materials

2.5 Concrete

Concrete shall be of the class indicated on the Drawings and shall conformwith the requirements of Specification Section 07100 Concrete and ConcreteStructures and the requirements specified below unless otherwise stated onthe Drawings or as may be required by the Engineer

The maximum size of aggregate for use in the manufacture of PrestressedConcrete shall be 25 millimeters

The main properties of concrete such as compressive strength at 28 days,Modulus of Elasticity (Young Modulus), and other properties that were usedfor the detailed design shall be confirmed by testing of samples of theapproved mix design The Contractor shall perform the tests in accordancewith the appropriate standards, or as may be required by the Engineer

3. Storage of materials

3.1 High tensile strength steel

The High tensile strength steel shall be carefully packaged to avoid moisturerust, during transportation to use the tight canvas, not to stick to oil, grease,salt, chemical fertilizers Transportation of high strenth steel shall not beassociated other cargos

While loading and unloading from vehicles to the stock yard or otherwise, it

is not permitted to throw down from above, not to be twisted and scratched.Any defect that damages the high tensile strength steel wire shall be thereason to check and it may be rejected

The High tensile strength steel must be stored in the tall warehouse,ventilation, not wet, when high tensile strength steel is pilied up, the steelmust be placed on the even platform at least 0.2 m high from the groundand should not pile up exceed 1.50 m

3.2 Reinforcement and built-in structures

All the steel before using must be checked including the documents forlabels, codes and categories

Steel must be separated in each type of diameter for easy use and checked

as needed, not to adhere oil, grease, paint or other chemicals

Steel must stored on the timber shelf so that the entire bars is higher thanthe ground at least 0.3 m

Prior to installation, the fabricated built-in items must be inspected forcorrection of marks, steel code, drawings and specifications

During storing, materials must be separated, absolutely not adhere greasy,asphalt, if adhering contaminants, materials must be cleaned

NGAI SECTION

3.3 Storage of cement

When transporting cement to the storage, canvas must be used to cover toavoid rain If the cement be moistured, put these cement bags aside andhave plan to use in advance

Cement placed in the storage, the storage ground must be tall, nostagnancy, no leaking from all directions around Cement storage shall be atleast 0.2 m higher than the background and placed on the airy floor

The cement bags pile no more than 8 layers, the bags are stored away from

a wall about 0.3 m, between the rows of cement bags must have walkway totransport

To ensure no degradation of cement, the time from production to use ≤ 70days

3.4 Storage of aggregates

Aggregate for concrete of beam must be stored separately, not mixing withaggregate of other concrete components

Sand, stone storage areas must meet the requirement hereunder:

 There is no stagnant water, have drainage ditch around

 There are layers of compacted crushed stones so as separatewith mud

 During use, the damaged surface must be remedied in time.The amount of sand and rock must be stored enough quantities forproduction of the beam

Each delivery of sand, stone must be checked for the dirt, flatness graincontent, and weathering rock content

II Casting yard and formwork.

1 Casting bed and formwork

I beams are the post-tensioning concrete beams

The Contractor will organize casting beds and concrete mixing plants tosupply concrete Service road will be provided for transportation of concrete

 The Contractor will fabricate enough formworks for construction;

2 Design of casting bed and formworks

2.1 Casting bed

Structure of casting bed must ensure convenience for placing reinforcingsteel and pre-stressing steel to get enough space for the erection and

Formwork consists of two parts: bottom and side formworks.

 Bottom formwork is made plate steel of 5 mm thickness, havingthe vertical and horizontal stiffeners made of steel Bottomformwork is divided into small plates After installing into thecasting bed, the plates will be connected by bolts

 Side formwork: made of steel plate thickness 4 mm, reinforcedwith V shaped steel Vibrators attach outside at even distance to

be used when concreting

 After the completion of installing vibrator into the side formwork,trial operation is needed to check the stiffness of the formwork,status of vibrator and stability

 Technical requirements of formwork:

* The firmness, durability, watertightness

 Install bottom formwork plates of 3m length and connect by bolts

 After welding done, detailed dimensions and flatness of each plate will

be checked, fix the error before starting next works

3.3 Side formwork

 Side formwork will be fabricated by plates of 3m length Connections

of plate will be made by bolts;

 Before casting the first beam, side formwork will be erected withbottom formwork to generally check all formwork of I beam

 Installing the vibrators to the side form by bolts

 Turnbuckle will be used for closing on the top of side formwork

 Turnbuckle will be installed in the two sides for supporting sideformwork;

 Side formwork will be installed only when completion of reinforcing

NGAI SECTION

steel and ducts

4 Installation of bottom formwork with casting bed

Each plate of the bottom formwork is linked with casting yard, may placeand pump cement grouting linking for each section before the joint weldingand then pumping cement grouting for the next section, or put the entirelythen pumping cement grouting The sequence of construction as follows:

 After fabrication of the bottom formwork plate meets therequirements then each plate will be installed on the casting yard.Link all bottom formwork plates by butt weld then grinding weldssmoothly Use the turnbuckles to tighten the bottom formwork withthe casting yard Check the overall size of the bottom formworkinstalled

 Pumping cement mortar M100 into the gap between the bottomformwork and the casting yard

 Repeat the above sequence of construction for the next segment

 Set and associate support structures for wall wing together withcasting yard

 Set and associate jacking beam with the casting yard

 Check the overall size of the entire bottom formwork with castingyard

5 Beam storage yard

Fabrication yard should have a suitable length The yard is compacted toK95 20cm of crushed stone will be placed on the top

The beams are chocked with concrete sleepers, dimensions 90x40x40 cm orequivalent at the location 150 cm from the beam head

Moving or transfering beams from casting bed to storage yard by gategantry

I. CONCRETE WORKS

Concrete is produced by batching plant at construction sites and transported

to the construction site by truck agitators Prior to delivery of concrete, thequality control and testing of concrete must be conducted along withdelivery records

With different structures: measures for placing concrete are shown in thedrawings of the construction methods

1. Components of concrete

The concrete beams are designed as specified in the Specification

Adjusting concrete mix design at the site will be conducted on the principlethat water / cement ratios will no be changed When aggregates is moist, itshould reduce the amount of mixing water, keep the required slump

2. Manufacture of concrete mix

Manufacturing concrete mix by batching plant Mixing concrete process shallcomply with the following provisions:

NGAI SECTION

 When mixing concrete, materials must be weighted accurately.Moisture content of sand and stones must be conducted inspectionregularly to adjust the amount of aggregates and water use

 Allowed tolerance when weighing shall not exceed the allowed values

 The accuracy of measuring equipment must be calibrated Duringweighing, regular monitoring to detect and correct promptly

3. Transportation of concrete mix

Batching plant is located next to casting yard so the transportation is veryconvenient and initiative in any situation

4. Placing concrete

Placing concrete must meet the following requirements:

 Closely monitor the status of formwork during the constructionprocess to settle in time if problems occur

 When it rains, covering to prevent concrete from raining

 The placing concrete must follow instructions of the Engineer

5. Compacting concrete

Different kind of vibrators may be used, but to ensure that after the concrete

is compacted the surface free from honeycombing

Compaction time for each location must ensure that the concrete isthoroughly compacted

when compacting concrete:

 When using poker vibrators, moving distance not exceeding 1.5 timesthe radius of the vibrator effects Distance to side formwork from 5-10cm, penetrating into the under concrete layer 5-10cm, whenfinishing each vibration of a place just to withdraw vibrator up, avoidcolision of vibrator into formwork, reinforcing steel and right in placeburied parts

 When using the vibrator must base on the figure and shape of thestructure and vibrator functions, through testing to determine thedistance of the vibrators

 When the concrete stop subsidence, no air bubbles, surface compacted, then stop vibrating

well- The placing concrete must be conducted continuously If interruptionoccurs, the interupption time must be less than the time of initialsetting, or less than the allowable time for re-vibrating the earlierplaced concrete

6. Curing concrete

After placing conrette, concrete must be cured in conditions of humidity andneeded temperature for curing and preventing the harmful effects duringcuring of the concrete

NGAI SECTION

Moisture curing: is the process for keeping concrete with moisture necessary

to the setting and hardening after shaping During curing, the concrete shall

be protected against mechanical impacts such as vibration, shock forces,loads and impacts, which are likely to cause other damage

7. Checking of the concrete samples

The limit compressive strength of concrete must be taken through testingsamples Each casted beam takes 09 samples, 03 samples tested after 72hours (3 days), 03 following samples is tested after 7 days, 03 remaingsamples to determine the 28-day strength The testing sample is cylinder150x300 mm or cube 150x150x150 mm

The quality of materials used for mixing concrete must be tested, the testmethods must conform to the relevant regulations

II. Tensioning Prestressing Steel

1 Preparation works.

1.1 Quality Ceritificates

The Contractor shall provide sufficient anchorage certification of themanufacturer Check the anchor system before stressing

1.2 Preparation work before stressing

- Check test result of concrete

- Check the test results of PC strand

- Check the manufacture certifications

- Check the tolerance when placing high tensile strength tendon

- Check and calibration of the jack, the pressure gauge will be used Ifbeyond the time limit must be re-calibrated

- Determination of friction coefficient of the jack and anchorage ring(determined separately for each jack)

- Check the threaded hole for high tensile strength steel tendon(cleanness, the space)

- Check the operation and safety procedures

- The contractor will establish mark points to measure the elongationand demand pressures as required by Consulting Engineer

NGAI SECTION

shape and dimensions Layers of reinforcement shall be separated bysuitable wire spacers Wooden blocks shall not be used

1.4 Threading anchorage ring.

Cleaning ring and strand before installation

2 Jack and sequences for tensioning:

- Jacks used to stress the tendon is Pre-stressing jack ≥ 290 Tons

- Use anchorage type of OVM or equivalent

- Jacks and anchorage must be tested before being put into use

- Tensioning sequence as in accordance with design method

3 Tensioning method:

- Jacks are hung on the support by the chain hoist Insert the jack in themanner that the jack head leans against anchorage of beam

- Firstly apply jacking forces 10% of design capacity

- Then use the ruler to measure metric length of the jack pistoncorresponding to each pressure level

- After jack achieves the design pressure, measuring the totalelongation compared with the actual elongation allowed by design

- Return the jack from design pressure to pressure 0 to close the wedgeand measuring wedge slip (if any)

- Calculation the elongation of the strand through linear interpolationmethod (taking into account the slip in the two ends of jacks)

4 Technical requirements of the process of tensioning prestressed

tendons

Post tensioning shall be carried out in accordance with an approved methodand in the presence of the Engineer unless permission has been obtained tothe contrary

Immediately before tensioning the Contractor shall prove that all tendonsare free to move in the ducts

Each anchorage device shall be set square to the line of action of thecorresponding post tensioning tendon and shall be securely fixed in positionand gradient to prevent movement during the placing and compaction ofconcrete

Except where dead end anchorages are cast in the concrete, tendons shallnot be installed until just prior to stressing Tendons shall be pulled orpushed through the duct in such a manner as to avoid damage to either thetendon or the duct

Unless approved otherwise concrete shall not be stressed until 2 testcylinders taken from it have attained a compressive strength of not less than80% of the specified 28 day strength as shown by standard specimens cured

in a similar fashion to the element unless specifically noted otherwise on the

NGAI SECTION

Drawings The test cylinders shall be cured in conditions similar to theconcrete to which they relate and in a manner approved by the Engineer.Where members consist of jointed elements the strength of transfer of thejointing material shall be at least equivalent to the specified strength of themembers

The Contractor shall establish the datum point for measuring extension andjack pressure to the satisfaction of the Engineer Allowance shall be made forthe friction in the jack and anchorage for pull in of the tendon duringanchorage

The tendons shall be stressed at a gradual and steady rate until the requiredextension and tendon load are reached or are approved by the Engineer Thesequence of stressing shall be as shown on the Drawings or directed by theEngineer

The force in the tendons shall be obtained from readings on a load cell orpressure gauge incorporated in the equipment and the extension of thetendons measured The extension of the tendons under the approved totalforces shall be within the limits given below of the agreed calculatedextension

Transverse Tendons for Segments: ±10% average for one tendon

± 7% for average of onesegment

Longitudinal Tendons for

If the measured extensions are not within the specified tolerance then theContractor shall submit to the Engineer his method of rectifying thediscrepancy

When the prestressing force has been applied to the satisfaction of theEngineer the tendons shall be anchored The force exerted by the tensioningapparatus shall then be decreased gradually and steadily so as to avoidshock to the tendon or anchorage

Full records shall be kept of all tensioning operations including measuredextensions, pressure gauge or load cell readings and draw-in at anchorage.Copies of records shall be supplied to the Engineer within 24 hours of eachtensioning operation

Unless otherwise agreed by the Engineer, tendons shall not be cut less than

2 days after stressing

5 Grouting of Ducts and Sheathing

Grouting trials shall be undertaken when directed by the Engineer TheContractor shall submit a detailed method statement prior to use in anytrials or in the works covering proposed materials, sheathing, anchorage andvent alignment equipment, grouting procedures and Quality Control for theapproval of the Engineer

All ducts shall be thoroughly cleaned out by means of flushing with waterand/or water/compressed air

NGAI SECTION

Grouting of ducts shall be carried out as soon as is practicable more than 4weeks after the tendons in them have been stressed and the Engineer’spermission to commence has been obtained If due to the requirements ofthe stressing procedure tendons cannot be grouted within this period thesheathing shall be sealed to protect the tendons from corrosion

Injection shall be continuous and it shall be slow enough to avoid producingsegregation of the grout The method of injecting grout shall ensurecomplete filling of the ducts and complete surrounding of the steel Groutshall be allowed to flow from the free end of the duct until its consistency isequivalent to that of the grout injected The opening shall then be firmlyclosed Any air vents shall be closed in a similar manner one after the other

in the direction of flow The injection tubes shall then be sealed off underpressure until the grout has set

The filled ducts shall not be subjected to shock or vibration within 1 day ofgrouting Not less than 2 days after grouting the level of grout in theinjection and vent tubes shall be inspected and made good as necessary.The Contractor shall keep full records of grouting including the date eachduct was grouted, the proportion of the grout and any admixtures used, thepressure, details of any interruptions and topping up required Copies ofthese records shall be supplied to the Engineer within 3 days of grouting

6 Protection of Prestressing Anchorages

As soon as possible after tensioning and grouting is completed, exposed endanchorages, strands and other metal accessories shall be cleaned of rust,misplaced mortar, grout and other such materials

Immediately following the cleaning operation the entire surface of theanchorage recess and all exposed metal shall be thoroughly dried anduniformly coated with an epoxy bonding agent conforming to AASHTO M235Class III in accordance with the manufacturers recommendations

The anchorage recess shall then be filled with an approved non-shrinkagemortar The mortar shall not contain aluminum powder, iron particles,chlorides, sulfates, fluorides or nitrates

Where the protection will form part of the exposed works the anchoragerecess shall be filled with concrete of the same quality and color as that ofthe adjacent concrete and shall be applied and cured in accordance withSection 5.1

Exposed surfaces of anchorages not in an anchorage recess shall be coatedfor corrosion protection with a coal tar epoxy or equivalent as approved bythe Engineer Prior to coating, all surfaces shall be wire brushed to removeall loose rust, mill scale or other deleterious substances, and the surfacescleaned with a suitable solvent to remove oil and grease

7 Curing

Wet (water) curing shall be provided in compliance with the requirements inSpecification Section 07100 - Concrete and Concrete Structures If theContractor elects to cure by any other method the method and details shall

be subject to the approval of the Engineer

A steam curing process complying with the following conditions may be used

as an alternative of water curing, if proposed by the Contractor andsubsequently approved by the Engineer

NGAI SECTION

The casting bed for any unit cured with steam shall be completely enclosed

to prevent steam from escaping and exclude the outside atmosphere

Two to four hours after placing concrete and after the concrete hasundergone initial set, the first application of steam shall be made Ifretarding admixtures have been used, the duration before application of thesteam shall be increased to four to six hours

Water curing methods shall be used from the time the concrete is placeduntil steam is first applied

The steam shall have a relative humidity of 100% to prevent loss of moistureand to provide moisture for proper hydration of the cement

Steam shall not be directly applied to the concrete During the application ofthe steam, the ambient air temperature shall increase at a rate notexceeding 22oC per hour until the maximum temperature is reached andshall be held until the concrete has reached the desired strength

In discontinuing the steam application, the ambient air temperature shallnot decrease at a rate exceeding 22oC per hour until the temperature hasreached 10oC above the temperature of the air to which the concrete will beexposed

The maximum curing temperature shall be from 60oC to 67oC

8. Handling, Transport and Storage

Gate gantry will be used to lift beams out of formwork, shifting and placingbeams to the stock yard

When lifting the beams out of formwork, beams should be further cured andkept moisture until the end of day 7th

When completion of the works, conducting to repair the defects of the beam

if any (small porous, uneven surface ) will be carried out immediately afterlifitng out of the casting bed, but must be directed by the Engineer

The beams will be numbered and casting date on the beams at the samelocation

Pre-cast pre-stressed concrete shall not be moved from the casting position

or transported until the concrete has attained a compressive strength of80% and 90% of the specified 28-day strength respectively

Extreme care shall be exercised in handling and moving cast stressed concrete members

pre-Pre-cast beams shall be transported in an upright position, shock shall beavoided and the points of support and directions of the reactions withrespect to the member shall be approximately the same during transportingand storage as when the member is in its final position If the Contractordeems it expedient to transport or store pre-cast pre-stressed units in otherthan this position, it shall be done at his own risk after notifying theEngineer

9. Marking of Precast Members

Each precast member shall be uniquely and permanently marked so as toshow its type and date of casting

2. Inspection of the records, materials and construction diary:

- To inspect a product of prestressed concrete beams, the Constructorshall present all the following documents:

+ Shop drawings that shows all of the changes allowed during theconstruction process Where multiple changes, the as-builtdrawing must be made enclosed with the original shop drawings.+ The document for proposed changes and allowing the change indesign

+ The test results of materials and certificates of quality productsfor raw materials or accessories of the beams

+ The partial inspection minutes such as: inspection of reinforcedsteel, inspection of formworks, the ground foundation, castingyard and inspection of placing concrete, etc

+ Construction dirary and other relevant documents as prescribed

3. Check and inspection of the actual product

- The exposed surface of the beam must be flat, smooth and uniformcolor

- Except for the projecting bars, which shall not expose out of thesurface of concrete No damage of the outer concrete surface such asporosity, edge breaks that exceed the permitted level as regulated

- Before repairing location such as coating cement grout, chop mortar,covering concrete the minutes of removal of formwork and the writtenpermission for repair by the Engineer must be made

- The tolerances listed in Table 2 are the allowable deviations forPrestressed Concrete structures These tolerances will be included inassessments for the acceptance of work

Acceptable Tolerances of Prestressed Concrete Structures

Width of girder flange +20; -10

Thickness of girder flange +10; -5

Compressive Strength Refer to Section

07100

NGAI SECTION

Curvature of the girder from the

longitudinal center line (plan view) < 10

- Testing frequencies shall be accordance with Vietnamese Standard:TCVN 9114:2012; 22TCN 247-98 or other international standardsubject equivalence being demonstrated by the Contractor and thesatisfaction of the Engineer of the Vietnamese standard

IV. Construction of I33m beam

1 Production Works

1.1 Production Yard Preparation

- Batching plant will supply concrete with capacity 60 m3/h or 72m3/h

- Internal Road are strengthened in proper manner to have strong ability

to serve girder production work

- Transformer station is prepared with the best quality Furthermore,Electric system including other electric devices is also prepared to meetrequirements

1.2 Forming Works

- Formwork shall be made in 03 parts:

 The bottom formwork: It be fixed into the concrete bed

 Side form: connect to bottom form work by bolts & tendons

 The end-girder formwork: including 02 units at two end-side ofthe girder

- Formworks shall be cleaned, smooth and applied formworkoil…

- After installing, adjusting and fixing rebar inside the form, theend-girder form shall be installed

- The internal form shall be installed in right position afterfinishing whole the rebar works, pre-stressed reinforcement works

- After installing formwork, it is checked by total station andsteel ruler 50m

1.3 Reinforcement Works

Reinforcement Works

- All steel lots should have certificate form the manufacturerssuch as: (diameter, number of lot, date of production, quantity of lot,producer, list of testing, etc) and test result for tensile strength,elongation, bend test for every lot which is purchased before taking itinto operation

- Reinforcing steel needs to ensure that the surface shouldclean

- Reinforcement will be fabricated at work shop to meet thedrawings Then, it will be transported & installed into form work

- All reinforcement shall be fixed firmly in position by steel wire.Connection welding shall be done only with specified in drawing orapproved by engineer

NGAI SECTION

- All reinforcement cages shall be transported, storage andmaintained in such a manner so that they are not bent and free of dust,grease, paint, rust

- The cover shall be kept by concrete spacers, which shall bepre-made and made of the same strength as concrete of girder

It is not allow to over permitted variation as following:

+ Distance variation of main reinforcement cover in comparison with design : ±15mm

+ Distance variation of reinforcement stirrup in comparison with design :

±15mm

+ Variation of steel vertical direction : ±15mm+ Thickness Variation of reinforcement cover in comparison with design :

±0.5mm

1.4 Duct Reinforcement Works

After installing one side of side formwork, installing reinforcing steel and PCduct with the sequence:

Installing steel frame and PC duct support, passing PC duct through position,binding PC duct with positioning support At joint of PC duct shall be covered

by adhesive tape to avoid concrete water leaking into PC duct Installinganchor seating into PC duct and install bolts to connect tightly with sealingformwork of girder head, soring under anchor seating is installed withreinforcing steel and fixed with positioning frame Before installing headsealing formwork, grouting hole and PC strand hole of anchor seating shall

be covered tightly to prevent from blocking PC duct

Slump flow shall be tested before placing concrete into forms

A checking minute shall be made during placing and the other minute forchecking massive concrete after completion of casting girders

- Time for starting and finishing concrete placement

- Slump flow, grade and mark

- Completed volume of concrete

- Outdoor temperature during placement

- Concrete sampling minute with number of samples, marks,positions of sampling

NGAI SECTION

Concrete hand-pocker vibrator are used for compaction

Curing girder are cured under wet condition, covered by canvas or jute andkept wet continuously After setting, concrete is cured at form until forms arestripped, all exposed surface of concrete shall be covered immediately bycuring agent

1.6 Pre-Stressed Reinforcement Works

PC strand lots mobilized to the site shall have certificates frommanufacturers, sampling for test of properties which are approved by theEngineer

PC strand lots shall be stored in storehouse, placed higher than floor 0.5m.Storehouse prevent from raining and sunshining

The unbond portion of strand shall be covered by the plastic hose and seal

to keep out mortar Those hoses shall be fixed into the end-girder form

1.7 PC Strands Tensioning:

a) Conditions to tension PC strands:

- Actual strength of girder concrete at site (shown in compressive test result)reaches 85% designed strength

- Passing through PC strands:

+ Before passing through PC strands, marking numbers of PC strands

on concrete surface at girder head, at both heads of PC strands shall bemarked the same numbers as specified in design

+ PC strand is passed each by each through PC duct, abundant length

at both ends of PC strands is 700mm After that installing anchors, wedgesand jacks

+ Marking to monitor during tensioning PC strands:

NGAI SECTION

- Using leveler machine to mark datum line on lower edge of girder head.Marking 3 points: 2 trim ends of two heads of girder, one point at middle inorder to monitor the camber of girder

c) PC strands tensioning:

- Using 2 jacks 250T to tension at both girder heads

- PC strands is tensioned with sequence from girder top to bottom withcable number

- Tension force of PC strands is calculated as formula:

Pc = Pk.K

Where:

Pc : Designed tension force

Pk : Theorical tension force (defined by design)

K : Friction coefficient of jack, anchor is determined through actualtesting

- Tensioning PC strands with each force as follows:

+ Step 1: (Tension to compare cables) Tensioning with force 0,08Pc ,stopping to mark to measure the elongation of PC strands

+ Step 2: Tensioning with force 0,2Pc

+ Step 3: Tensioning with force 0,4Pc

+ Step 4: Tensioning with force 0,6Pc

+ Step 5: Tensioning with force 0,8Pc

+ Step 6: Tensioning with force 1,0Pc

+ Step 7: After step 6, maintaining pressure in 5 minutes, after thatseating anchor and lowering jack to 0,08Pc Measuring anchor droppingand lowering jack to 0, removing jack

In each step, from step 2 to 6, when force of 2 jacks is enough, keepingjack forces to measure elongation data of PC strands

When PC strand tension is completed, the camber of girder shall bemeasured

+ Determination of PC strands elongation:

L= K ×

∆

PK : Designed tension force

E, F : Deformation module, conic section

- Relative elongation of PC strand at each pressure is determined by:

i i

∆li : elongation of PC strand at force i

∆li1, ∆li2 : elongation of PC strand at force i of jack 1 and of jack 2

∆l1, ∆l2 : elongation of PC strand measured at step 6 at jack 1 andjack 2

∆S1, ∆S2 : PC strand dropping measured at step 7 at jack 1 and jack

2

- Allowed errors when tensioning jack:

+ Allowed errors of tensile force ± 5%

+ Allowed errors of elongation ± 5%

- Results of tensioning process is recorded in forms specified by the project

1.8 Grout Preparation:

a/ Grout proportion includes:

+ Portland cement

+ W/C ratio: N/X ≤ 0.4

+ Expansion admixture + plasticizer admixture

The mobility of grout does not exceed 15 seconds

Bleeding rate does not exceed 2%

- Grout is mixed with sequence: