04.chapter ii

Hanoi – Hochiminh city railway line Do Vang Bridge’s construction bridges safety improvement project technology of beam casted on scaffolding

CHAPTER II: TECHNOLOGY PROCESSI. CONSTRUCTION SEQUENCES

Concrete beams of Do Vang Bridge are casted in place on the scaffolding. Construction scaffoldings are made up of shape steel including of: longitudinal beam

H200 and horizontal beam and scaffolding system for supporting side formworks.Side formworks, bottom formworks, internal formworks with splint system, through

bar must be stably, firmly throughout concreting process.After completion span 2 and span 5, formwork scaffolding will be transferred to

construct the next spans.Concrete shall be provided from batching plan at Site with capacity 60m3/h to the

constructed position by truck mixer and concrete pump. Construction sequences

+ Step 1: Land levelling at position of girder construction, filling sand and compacting to K95. Installing the concrete plank 1x1x0.2m.+ Step 2: Installing the scafolding, longitudinal beam H200 and horizontal beam H200+ Step 3: Testing of scaffold. + Step 4: Install external formwork, side formwork+ Step 5: Install reinforcing steel, pouring concrete+ Step 6: Stretch prestressed cable.+ Step 7: Removal of scaffolding, internal formwork, pushing scaffolding system.+ Step 8: Connect projecting reinforcement couplers of diagraphm, reinforcement, diaphragm formwork. Placing concrete and stressing horizontally prestressed cable of diaphragm. + Step 9: Construction of the next span.

II. TECHNOLOGY STEPS

1. Land levelling

Land levelling at position of girder construction, filling sand and compacting to K95.

Installing the concrete plank 1.2x1.2x0.18m2. Production and erection of scaffolding

Scaffolding, formwork must be designed to resist any unfavouble displacement during

superstructure construction process.

Construction scaffolding is included:

+ Supporting scaffolding of side formwork

+ Installing the scafolding, longitudinal beam H200 and horizontal beam H200

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Figure 1: Span structure’s construction scaffolding

3. Testing scaffolding

This test aims to remove the settlement of scaffolding system, check the pressure

bearing ability of scaffolding. Load test results must be reported immediately to The

Engineer.

4. Install beam formwork

Concreting formwork design

+ Bottom formwork is combined by flat formwork 1x2m, placed directly on

diaphragm steel shape H200..

+ Side formwork and flange beam is combined by flat formwork and special

formwork put on modules of steel shape H200x200, wihch are associated with

diagram steel shape H200x200.

+ Core formworks shall be fabricated by modulus 0.25x1.0m, fitness, easy

working, and convenient removing. The formwork is designed by the type of

modulus 1m including formworks- supporting bars- bands, ready erected on the

ground and hoisted into its position.

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+ Elevation of formwork at each section must be included design deflection of

the bridge and deflection resulting from pre-stressing and deformation of

scaffolding.

Install bottom formwork

Erection sequence as follows:

+ Formwork boards are placed directly on the diaphragm steel shape H200x200

+ Erection of formwork boards with the length 2m is in the direction of bridge

and parallel to connecting centre line between two piers.

+ After completing bottom formwork installations, in a maximum distance of 4m

between sections, measure the level to adjust the level of beam bottom.

+ Insert the steel wedge below the formwork to adjust the level of formwork

surface (beam bottom).

+ Installation of a special formwork at pier position

Installation of external wall formwork

Erection sequence as follows:

+ Installation of outside scaffolding system and protective handrail.

+ Completely erecting formworks modulus and supporting frame for beam web

consisting of: web formworks, supporting frames.

+ Hoisting each formwork modulus and supporting frames into exact position.

+ Adjust level of formworks.

+ Tighten the connection bolts, fix geometric position of formwork segment and

install the next segment until finish a span of beam.

Installation of core formwork

The installing sequence shall be as follows:

+ Formwork system and supporting frame of core formwork shall be installed in

every modulus at 4~6m length, suitable with the capacity of the hoist.

+ Hoisting each formwork modulus into exact position.

+ Adjusting elevation and coordinate of formwork.

+ Tighten the connection bolts, fix geometric position of formwork segment and

install the next formwork segment until finish a concreting segmentation.

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5. Beam bearing installation

The Contractor will install bearing before casting concrete. Detailed construction is

follows:

Step 1

Cleanning reinforcement of bearing stone, installing formwork of bearing stone,

casting non-shrinkage motar for bearing stone construction.

Step 2

When the motar of bearing stone meets requirements of strength, locating exactly

bearing position, defining the horizontal and vertical position of bearing stone,

installing the bearing.

6. Installation of reinforcement, duct and high strength cable

Installation of reinforcement

Reinforcement is fabricated at yard according to the designed geometric dimension,

numbered and bundled for hoisting into installed position.

Sequence for installing rebar will be prepared by construction team and informed to

foreman during installation of beam rebar with the below principles:

+ Fully installing bars in accordance with the size and location indicated in the

design.

+ Steel structural members must be removed or fixed at designed position by

using supporting bar, chock or tie to resist the excessive movement or bending

during construction process.

+ The distance from formwork surface to steel structural member must be

remained by using supporting bars and chocks. The chocks must be placed in a

suitable distance to make the formwork be free from cracking or excessive

deflection.

+ The chocks must be enough hardness, strength and suitable shape to not form

holes around them.

+ The position tolerance for internal reinforcement of concrete:

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Bar detail and bending dimension for the rebars must satisfy the

requirement stipulated in Section 5.11 of Bridge Construction

Instruction AASHTO LRFD 98.

The installation tolerance for the super structure as follows:

d ≤ 200 200 < d < 500 500 <d ≤ 2000 d>2000

Tolerance (mm) 5 10 20 30

In there: d may be:

Dimension by measurement direction (mm)

Height of cross section (mm)

Installation of Duct and high strength Cable

Install holing duct:

+ The holing ducts for high strength tendon are put into designed position before

concreting. The duct is installed segmentally (according to produced length) ducts

are connected together with linking pipe and joint tape around to prevent motar

from inner leakaging.

+ To fix ducts into reinforcement mesh, using D6 bars supporting below and

binding into the mesh at each coordinates adjusting position of the strand

according to design requirements.

+ The head of duct is inserted in the anchor head fixed into beam formwork.

+ The duct is associated to ventilation pipe and grouting chute at the lowest and

the highest points to ensure the pumped grout will completely seal the duct, free

from air bubble.

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Figure 5 : The process of connection cladding Figure 6: Setting mortar

Figure 7: Field duct connection

Install duct and high strength tendon:

+ Install duct and high strength tendon, using cupler to connect tendon.

+ High strength tendon will be cut up to designed length, bundled and inserted

into the duct then put into place.

+ Fix cable into head of dead end, locate the dead end.

Notes when installing duct and tendon:

+ Duct position must be installed in right designed place within allowed

tolerance.

+ Curve of cable must be smooth when visually check.

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Wrap joint tape to be sealed and free from grout leakage


+ Duct must have enough tightness so that mortar can not run into there.

7. Placing concrete for beam

Concrete mix design

Concrete of approach beam of Do Vang bridge has relatively dimension and quantity,

thus mix design work greatly affects the concrete quality. The mix design shall be in

accordance with requirements of Specification.

Concrete shall ensure to be enough strength, waterproofing as requirement of design

also meet demand of yield to ease the construction with minimum cement content.

Minimum compressive strength of cylinder specimen at 28 days shall be 40Mpa to

ensure concrete reach to strength 40Mpa as designed.

In any case, the required slump of concrete shall be 14 ± 2 cm. It shall be rejected if it

is not as requirement. Do not add water to fresh concrete.

Concrete shall have enough adhesiveness and flexibility to ensure it is not segregated

throughout concrete transporting and placing process.

Water-cement ratio in concrete mix shall be less than 0.40.

Concrete mortar shall have setting time over 6 hours.

The parameters of beam concrete:

+ Grade: 40 Mpa

+ Slump: 14 ± 2 cm

Concrete materials

Beam concrete of Do Vang Bridge as shown in the Specification of Project has

cylinder strength 40MPa.

Mix design shall conform to Specification of Project.

Admixture of concrete is produced by Sika manufacturer. This is a super-plastically

high-tech substance at the thirdly versioned polyme origin to push concrete harden. The

admixture will affect on the below characteristics of concrete:

+ The ability of reducing water is so high.

+ To be deliveried in a great distance.

+ The yield strength is high (decrease the works of placing and compacting)

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+ Boost the development of strength

+ Improve the ability of creeping, shrinkage.

Construction plan layout

+ Currently, construction plan of the Do Vang Bridge has already leveled off material

store yard, reinforcing yard to ready for installing, testing load and placing concrete for

beam.

+ Night lighting system: The Contractor shall arrange fully lighting system along the

service road, beam and all constructing positions throughout the concreting process. The

bulbs used during construction have capacity 500W and shall be disposed at the distance

of 510m per bulb. The minimum illumination level for concreting is 30lux/m2. (When

it comes to horizontal concrete plane – Refer to “Bridge constructing manual” composed

by Pham Huy Chinh- Construction Publisher 2007).

+ Standby power system: The Contractor has standby power system 250KVA in case

of power loss. This system shall be always maintained and checked to find out defects

and treat immediately.

Construction Equipment

No Equipment Unit Quantity Note

01 Mixing plant 60m3/h each 01

02 Mixer Truck each 03

03 Pumpcrete machine Puztmaiter each 02

04 Generator 250KVA each 01

05 Crane 40T each 01

06 Purchase tackle each 04

07 Jacking and oil pump house Set 02

08 Mortar mixer and pump Set 02

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09 Surveyor's level each 01

10 Tachometer each 01

11 Vibrators each 15

12 Pumpcrete pipe m 250

13 Welding machine 400A each 04

14 Pump 60m3/h each 02

Arrangement manpower

No Equipment Unit Quantity Note

01 Engineering person 03

02 Investigation person 02

03 Woker drive crane person 04

04 Worker support crane person 06

05 Woker drive electric person 02

06 Woker drive mixing plant person 02

07 Worker drive shovel person 02

08Worker drive pumpcrete machine

person02

09 Woker weld person 15

10 Woker jack person 05

Concrete mixing

Use batching plants that can automatically measure and weigh at Site. The scales shall

be checked accuracy, meet the Specification of Project as stipulated.

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Concrete of each batch shall be in accordance with Specification as required.

The slump of concrete must conform to requirements. Therefore, before each concrete

placing time, determine the material moisture to caculate suitable water content for

concrete mix.

Provide concrete

Concrete shall be provided from batching plant to constructed position by truck mixer

and concrete pump.

Time from mixing, placing to compacting concrete is not over 90 minutes to ensure

the works of concreting finish before concrete setting.

Components and slump of concrete mix shall be tested and trial pumped to ensure the

quality of concrete and construction conditions simutanously suitalbe with technical

funtions of pump.

When construction in hot weather, the external surface of concrete must be covered or

whitened to restrict sunlight effect causing hot concrete.

Method for decrease concrete mix temperature

The Contractor intends to cast concrete from 16 p.m to 10 a.m next morning. In case

of daytime construction, the Contractor shall not construct on the day that temperature is

over 35C.

Construction in nightime to reduce temperature, direct sunlight causing hot pump pipe

and newly placed concrete.

Concrete mix temperature from batching plant shall be controlled to not excess 25C

and when placing it is not over 35C. For these purposes, beside construction in nightime

to decrease temperature, the Contractor also use the following methods to decrease

aggregate temperature:

+ Spray water on balast, gravel: Ballast, gravel in store yard shall be sprayed

periodcally for keeping wet surface to create evaporating mechanism so that

reducing agrregate temperature.

+ Use cool water to mix concrete, water tankers shall be covered from sunlight.

Pour concrete

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+ Concrete is poured by mix truck and pumping machine

Concrete placing direction: Concrete shall be casted from the low head to the high

head of beam and placed alternately on all beam webs, ensure that height defference

between these webs is not over 50cm.

Pour concrete vertically by each segment that splayed a 450 angle against to horizontal

direction.

Attention when pour concrete

+ Slump of concrete must be as required. Therefore, before each concreting

batch, it is necessary to determine the moisture of material to calculate the suitable

water content for concrete aggregate.

+ The height of the concrete to fall is not more than 1.5 m to avoid segregating.

+ Fresh concrete is poured into formwork by a small amount and using methods

to remain rebar not movement during concreting process.

+ Mixxing speed must ensure that when pouring the above layer, the below layer

has not yet cured to create perfect bonds between layers.

Tamping

+ In the concrete mix, the Contractor has used superplasticizer with high

mobility of manufacturer Sika to decrease significantly placing and compacting

work.

+ Fresh concrete must be placed into formwork and compacted for each layer

from 250mm to 300mm thickness. By this time, compacting to the previous

concrete layers.

+ During compaction, at the position near ducts, pay attention to advoid touching

the duct to be broken. Do not use vibrator to push concrete.

+ Special attention to concrete quality at anchor heads.

Curing concrete

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Curing for concrete beam casted on scaffolding is conducted immediately after

finishing a surface area of concrete beams. Usually use wet sacks to cover on concrete

surface around one hour or when the concrete surface will begin to dry.

After finishing surface and until the surface can resist water (usually after 2 hours of

concreting) must water regularly to the concrete surface which face is finished. When

finishing pouring concrete for girder segments, watering to cure all concrete and wall

formwork. After removing the formwork must water to the concrete regularly throughout

day and nighttime.

Water for curing process shall be fresh water used to mix concrete.

Setting time must prolong at least 7 days from finishing of beam concrete.

Emegency occurrences that may happen and resolving method.

Treatment method in case of work suspension because of Force Majeure.

The concreting work shall not be executed in the following cases: hard rain, flood,

storm, or the conditions for placing concrete still not ready…

In the event that concreting process is suspended because of the interruption in

concrete providing source (long-time traffic jam, accident…) the problem shall be

resolved as below:

+ Use the standby mixing plants at the Site.

+ If the quantity of concrete required to place is further more than capacity of standby

mixing plants, the construction must be suspended and the Contractor continuously

compacts to finish the casted concrete. In the vertical direction, concrete shall be

made by diagonal section bias an angle 450 against horizontal plane. This special

construction joint shall be treated, roughed in accordance with procedure and

specification for the next concreting stage.

Measure to prevent honeycomb:

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Honeycomb at concrete is easy to happen because of special shape of box girder.

Positions where honeycomb can happen and method which is carried out in process of

pouring concrete to prevent honeycomb is showed in below table:

No. Position where honeycomb can

happen

Reason Preventative measure

1 The lower chamfer of web Concrete pouring to

web is easy to flow

to bottom slab

Need to guide workers

not hesitate when

compact concrete

Workers hesitate

when compact

concrete because

concrete flow to

bottom slab

The lower chamfer

of web can’t be

compacted well

because outside web

isn’t straight

The vibrating tampers

are often associated

with a burning

bamboo or a straight

pipe to pass thread

along shape of

diagonal web

Projector flashlight

into the side of web

These parts will be

hammered handwork

by wooden hammer

2 The angle of bottom slab

It is difficult to

compact by vibrator

Vibrator will be

associated with a

straight bar to

compact that part.

3 The lower part of cladding The claddings will Pour concrete slowly

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prevent compacting

concrete below them

and compact concrete

more carefully

4 The anchorage zone Much reinforcement Compact carefully

Beam casting formwork

No. Problem Resolve

1

Load capacity of formwork Before fabricating the formwork shall be

caculated, designed to ensure enough load

capacity. Checking their quality and geometrical

dimension before leaving workshop.

2

Formwork that is bad

quality, defected during

transportation

The formworks shall be checked, taken-over in

quality and geometrical dimension to

immediately discover and substitute the defected

boards.

3

The camber of formwork

resulting from designed

camber of the bridge,

stressing prestressed cable,

scaffolding deformation

During installation, the formwork elevation shall

be adjusted to be suitable with the camber.

8. Prestressed cable tension

Preparation work

It is necessary to make sure that before constructing all persons attending directly in

stretching works, especially technicants and stretching team leaders must have full

knowledge of stretch controlling steps to ensure the technical quality and safety

regulation.

Check concrete strength (taking sample before stressing). The strength shall reach to

90%Rtk (90%*40Mpa = 36 for cylinder sample).

Check jack, pump, jack bracket, chain hoist and work platform.

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+ Jack, pump for stressing shall be checked and approved before using.

+ Jack and pump shall be inspected by specialist authority.

+ Jack shall be inspected in the following moments:

Before using to avoid accident or occurrence.

Change jack set.

+ Anchor test:

Anchor using for Project must be in accordance with Specification and

inspected to pass testing criterium and approved by Engineer.

Anchor using for installation shall be free from crack, warp, and the chap

must be sealed with anchor.

Show stressing steps on the visble positions for the stressing team leader.

Fill up enough points stipulated in stressing note.

Stressing equipment.

Prestressed Cable

High strength cable shall use kind of tendon as 7 lowly saged plies 12 strands 15.2m

bundled cable Grade 270 according to ASTM A416 – 90A standard.

No Item Value

1 Nominal diameter 15.2 mm

2 Area of cross section 140 mm2

3 Ultimate strength 1860 Mpa

4 Yield point stress 1670 MPa

Prestressed cable shall be protected in store that has screen, be dry, apart 30cm from

the ground.

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Pretressed cable must have Certificate of Producer approved by Employer and

Engineer.

Test for tendon in accordance with Design Document and criterium: breaking force,

elastic modulus, yeild strength, elongation, dimension of each ply in tendon, condition of

external surface. Any change that not be in accordance with Design Document shall be

approved in writing by Design Unit, Employer, Engineer beforce constructing.

Anchor

Use imported anchor of OVM manufacturer for cable 15,2mm .

Imported anchor must have Quality Certificate of Manufacturer.

Jack

All of jacks, oil pumps shall be inspected before using.

No

Jack

Type of

Pump

Area Strain Sroke

NoteName Mark

pittong

(cm2)

max

(KN)

pittong

(mm)

1 YCQ500Q 0707 ZB4 - 500 1000 5000 200Horizontally

stretching

2 YCQ500Q 1001 ZB4 - 500 1000 5000 200Horizontally

stretching

Prestressed cable tension

Use one-head tensioning method. Using jack 500T applying for tendon as 7 lowly

saged plies 12 strands 15.2m bundled cable.

Stretch every twin cables symmetrically through centreline of beam in the following

sequence:

+ From centerline to outside.

+ From neutral axis to outside.

Sequence of stressing tendons on each segment: Stressing longitudinally then

stretching horizontally prestressed cable of bridge.

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The operation as follows:

Assemble anchor head

Picture 8: Cable cutting before anchor assembly

+ Anchor head must be cleaned with petrol before installing.

+ Lengh of strand end is caculated from anchor pad surface L lengh of jack +

15cm for stressed end and 0,6m for unstressed end. Then they are cut or staggered

in order, chamfered around and erected guide head to facilitate for anchor

installation .

+ Using two crossed guide forks to fix strands in every queue respectively to

socket queue of anchor head, then anchor head is passed through strands.

Put wedge (anchor bolt)

+ Check the type of wedge before putting. The wedge, anchor, seating shall be

one group and fit with diameter of strand. The wedge shall be washed clearly by

petrol before erecting.

+ Anchor head and seating shall be putted adjacently.

+ Use one steel pipe (inside diameter 16 - 20, lengh 2m) to reeve each strand,

impact wedge into socket to ensure wedge head of a full set to be flat, not

staggered.

Erecting voided plate of jack end

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+ Using two crossed guide forks to fix strands in every queue respectively to

sockets at voided plate of jack end then this plate is passed through strands.

Erecting jack:

+ Jack and pressure gauge shall be tested before using.

+ Jack is hanged in bracket by a chain hoist 1,5T to easily control elevation of

jack during stretching.

+ Jack shall be passed through strands by conduction plate and putted adjacently

with pad plate that be fixed position by pushing self-tightening device to stretching

head.

Pulling cable

+ Before cable tension, ensure that the axis of jack and the axis of strand at

anchor head shall coincide and jack head shall be put closely with seating.

+ Cable tension shall only be carried out when the strength of concrete is equal to

90% of the design strength.

+ Strain operation shall be proceeded to achieve the force as required in drawing

or by Engineer. The error of required force for each strand is only within 5%.

The error of total force in component is within 5% of the required value.

+ During strand anchoring process, take notice to mark the strand to measure the

anchor sliding. If the average of anchor sliding is more than 6mm, the cable shall

be released and pulled again. Thus cable could be pulled excessively to

compensate for the unpassed anchor sliding and expansion if the maximum tensile

force is not over 80% of rope cap.

+ Tension sequence:

Tensioning: Tensioning force is often equal to

10% designed force of strand. Mark location of strand to measure expansion.

Increase the force respectively by levels 0.2P;

0.4P; 0.6P; 0.8P; 1P. Measuring expansion for each force level (P is the

designed force that included anchor sliding).

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Increase tensioning force up to over 1P if cable

doesn’t achieve designed expansion, the increased force is equal to loss of

prestress of cable resulting from unpassed designed expansion but not over

80% rope cap.

Driving jack

+ Data for strain process shall be recorded as follows:

Order Level TensionGauge value

Expension (mm)

DesignMeasuring

valueActual

expension

1 0.1P

2 0.2P

3 0.4P

4 0.6P

5 0.8P

6 1.0P

7 Seating

8 Anchor sliding (mm)

9 Actual expension (mm)

+ The main method to determine exactly jack force is measurement of pump

pressure that included prestress loss of jack and anchor. This pressure is read by an

adjusted pressure gauge placed at pump station.

+ Attentions in cable strain process:

Chain blocks hanging jack shall be disengaged

when jack begins to bear force.

The route of piston is limited, so expansion in

each force level shall be concerned regularly to avoid exceeding the route.

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Pressure of jack shall be increased regularly and

decreased slowly and gradually (wedge not keep cable often occurs during

decrease jack pressure because of reducing jack pressure too fastly then

shorting cable but don’t pull wedge follow in).

While stretching stressed cable, don’t stand to

face the bunched cable (behind jack or anchor) and in the above position at its

stressed head.

Measure expansion of strand

+ Before tensioning, expansion of strand shall be adjusted by area and actual

elasticity modulus of strand according to cable certificate or testing result.

+ Expansion of strand shall be measured through the running out route of piston

at each pressure level. Another value is also measured to compare. This value is

measured from jack end to a solid thing (pointer) fixed in a strand.

+ When tensioning force in strand meets requirement, measure strand expansion,

the error of the expansion is not over 5%, if it exceeds this limit, stop stretching to

find out reasons before continuing to stretch.

+ The details for measurement and calculation of cable expansion refer to in Appendix

No.3.

Diagram 9. Measurement of cable expansion

+ Attentions when measuring expansion:

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Expansion measuring device shall parallel to

axis of jack (be perpendicular to the bottom of jack).

Wedge sliding at unstrained end (or not yet

strained) shall be determined by using a wooden voided plate to reeve through

strands to a given distance from wedge surface (about 10cm), spraying paint to

strand for marking distance. This work just carries out when strand was

stretched “turning cable”.

Remove the jack

+ Removal sequence of jack as follows:

To tranfer all of load from jack to anchor head

(gauge pressure goes down to 0).

Completely retract piston (recover jack to

original status).

Draw out jack by pulling handhold of clamp in

jack end.

Emmegency occurrences that may happen and resolving method

No. Problem Resolve

1

One or more strands are

breaked.

Removing and substituting the defected strands

and stressing again when find out one or more

strands are breaked.

2 One or more bunched cables

don’t reach elongation as

designed.

In case the tensile force is enough but the

elongation excesses the allowed limit then check

whether bunched cable is distored at any position

or not, check jack, journey of piston and gauge.

If all of them work normally, report to the

Supervision Engineer to resolve.

In case that pressure factor in gauge hasn’t 25


reached to designed level yet but the elongation

of bunched cable has already met or overtaken

the designed value then stop stressing, check

whether bunched cable is distored or not, check

jack, journey of piston and gauge. If all of them

work normally, report to the Supervision

Engineer to resolve.

9. Grouting the duct

Grout and grouting works must be in accordance with requirements in section 19-

TSP4-9 of Specification of Project, prepare prestressing works to ensure strands shall be

grouted immediately after prestressing.

After removing jack, the excessive sections of trand shall be cut off. Use mechanical

machine to cut (not use thermal methods such as oxy – acetylen torch or arc welder...).

The distance from cutting position to anchor head is 3cm.

Openned anchor head shall be sealed by concrete that has same grade with girder

concrete. Grouting pipe shall be put in its position before casting to seal anchor head,

surface of anchor head and bearing pad shall be cleaned clearly. Surface of concrete

thereof shall be roughened to increase affinity with the anchor head concrete.

Fill gap between steel and cable sheath by cement grout to prevent strands from

corrosion and concrete adhesion.

Grouting work for each steel kind shall be completed as soon as possible after

finishing stretching works but not over 5 days. At the same time, the grouting work shall

be carried out when the anchor head concrete has enough strength.

Use mixer when mixing the grout, the mixing time is not over 4 minutes. Pump grout

within 20 minutes after batching, or check the mobility again before pumping if the time

is over.

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Figure 10: Visit mortar pipe at field

Grouting work done by the following diagram:

* Inspection of Mobilization of Equipment & Worker

* Approval of Materials and Mixing Proportion

* Setting equipment (Grout mixer and pump)

* Setting grout hose

* Mixing with approval mix proportion

* In-situ testing of grout

* Grout shall not be interrupted per duct

* Check condition of discharge grout

* Maintain pressure of pump 0.5MPa

* Close injection hose with pressure 0.5MPa

* Stop pumping

* Keep verticality of hose and fixed

(after 1 day of grouting)

Preparation Work

Check Ventilation and Cleaning PC Ducts

Mixing Grout

Injection of Grout

Cutting Grout Hosehose

Check hardness and bleeding of grout on grout

Preparation work:

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Visit mortar pipe


Before the mortar, the mobilization of equipment and manpower will be monitored

and Engineer approval. Records of grout mixer and pump must be attached.

The proportion of materials and materials is separated proposed.

Equipment mixers and grout pumps will be arranged

Head pump is fixed with head in beam

Check ventilation and clean cladding

Tap air from the compressor is connected to a first hose and air pump grout into the

cladding will be given. The ventilation tube of the cladding tested at the other end of the

hose pump grout,

At the same time, excess water and waste materials will be blown out.

If not ventilate is tube blocking . In this case, the location rules and conditions must

be checked quickly to make remedies.

Mixing mortar

Each batch of mixed reality will follow the approval rate of mixing.

Mixing process as follows:

1. Water + Addition → 2. Cement (Mix in 4 minutes)

After mixing is complete, the grout will be put through membrane filters with the

largest mesh is 1.2mm before being pumped.

After mixing, in the field experiments will be carry out as table:

All mortar shall be filtered through a membrane filter with largest mesh is 1.20mm

before being taken into the pump.

Mortar shall be used within 30 minutes after each mix batching plants to ensure flow

and swelling degree.

Grouting

Open all the vent mortar

The grouting nipple of the pump is connected to a first loss of the grout pump beams.

Arrange the pictures in the pump.

Mortar shall be pumped through pipes and exhaust flows continuously through the

first discharge door after through charging door, until no longer the presence of water or

air, only the mortar extrusion characteristics, as at this dicharging will was closed.

The pressure pump at discharge door shall not exceed 1.0 MPa.

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After closing the discharge door, 0.5 MPa pressure will be maintained within a

minute.

After maintaining pressure within one minute, the pressure of the pump inlets will be

reduced and conditions of the mortar in the collection tube will be determined mortar

have reduced flow or pressure.

Next on stage, pressure will be increased to 0.5 MPa. And charging door will be

closed. ( Pressure 0.5MPa →Pressure drop → Pressure 0.5MPa → Closed discharge

door).

The closed discharge door and charging door will be carry out by measuring levels of

tightly and locked of pump nozzle.

After completed pumping grout, grout pump will be maintained vertically. The length

of the hose to pump concrete road surface larger than 1 meter, so in one day.

In the case grouting work is interrupted by an incident on machinery or other reasons

prior to completion, all seats will be the mortar has been pumped out exhaust pipes by

water is pumped from the pump or by the set others were immediately relevant.

Cutting nozzle

After a day mortar pump, the steam emission was checking by eyes in the pump

nozzle to reveal that legacy. If you see the steam emission in the nozzle exit, it will be

accepted for the grouting work in the nozzle to reveal it (the cock on girders).

After determining the steam emission, the excess hose will be cut close to the surface

of concrete beams.

Attention during grouting process:

+ The grout pumping equipment shall be able to work continuously without

deformation in pressure.

+ Pump should have the pressure distribution ability of minimum of 0.7Mpa and

shall be mounted with manometer with biggest readings is 2Mpa

+ Pressuremeter shall be verified prior to use.

+ The inlet and outlet tubes shall have the minimum length of 400mm, and

eternal minimum diameter of 20mm.

+ The average pumping speed inside the tube shall be from 6 - 12m/minute

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+ Valve operator should wear protection glasses to avoid the high pressured

grout of plashing into the eyes.

+ As soon as the stressing is completed, the grout pumping works shall be carried

out as soon as possible.

+ It should not grout in hot weather when the temperature outside is greater than

32C.

10. Removal of scaffoldings, formworks

Move scaffolding, beam formwork after finishing prestressing cable tension.

Removing work shall be as follows:

Removing core formworks

The formworks shall be fabricated by modulus 0.25x1.0m, fitness, easy working, and

convenient removing. After beam concrete reachs to required strength, the formworks

shall be removed as following sequence:

+ Cut-off and remove the supporting bars

+ Remove banding bars

+ Remove the formworks.

+ Cutting the supporting bars, bands and formworks outsite by service holes with

dimension 2.0x1.0m disposed at two sides of top slab of box girder.

+ Replace core formwork to construct the next span.

Moving bottom formworks, wing formwork and longitudinal beam H200 and

horizontal beam H200

+ Cut-off and remove the supporting bars to lower elevation of flange formwork,

bottom formwork.

+ After moving formworks, replace horizontal beams H200 and longitudinal

beams H200 and use crane to move to next position.

Scaffolding system

+ Remove scaffolding system to the next position.

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04.chapter ii

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