viaduct 2 final method statment

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WORK METHOD STATEMENTVIADUCT Page

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1. SCOPE

This statement describes the method to be followed for the bridge (Viaduct) during the different construction stages and activities as detailed later.

2. REFERENCES

-Jordan Code of Practice for the design of formwork.-Approved shop drawings.-Project specification.-Specification for highway and bridge construction – ministry of public works and housing.

3. METHODS:

A- GENERAL EXCAVATION WORKS

1. Access roads will be provided to the main bridge during construction to insure delivery of construction material to the site. Maintenance of access road will be done through the construction phase. This activity is performed by the General Contractor.

2. Excavation to the design level as shown on the drawings and sitting out will be done outside the foundation line to provide enough working space for formwork, water proofing, and drainage.

3. Any electrical and or drainage works related to the bridge and their connection with main lines will be prepared in advance to avoid delay of work.

4. The site levelling and surveying works will be executed by the general contractor after the engineer's approval of the shop drawing for the following :

i. -Abutments structure. ii. -Piers and their foundations.iii. –The box girder pre-stressed slab.iv. –The pre-cast post-tensioned girders and its relevant deck slab. v. –Pre-cast elements related to the viaduct.

5. General site levelling outside the bridge area will be executed after finishing the main excavation and backfilling of abutments and peirs.

6. External backfill for external service and access will be done on completion of the bridge structure.

B- FORMWORK

1-Foundation formworks

Type of formwork for foundations is rectangular; plywood form lining supported externally by horizontal and vertical timber frame is used.

2-Peirs formworks

A formwork composed of a prefabricated steel mould supported by structural steel sections for

the circular piers will be used. The design calculations for the form mould will be attached

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The formwork of the remaining piers P5 and P6 will be fabricated using fair face plywood

boards supported with timber joists serving as wailers and Hunnibeck soldiers in the vertical direction.

3-Deck formwork

i. Deck slab shoring system consists of two main items:

Propping of (1.30m x 0.90m) grid of a cup lock system.

Steel tube 48mm outer dia 3.2mm thick vertical props (standards) in

different lengths connected together using spigots to form the required

height.

Ledger pipes of the same type forming horizontal bracing.

Diagonal bracing near the edges of slabs (steel pipe 6m length 48mm.

dia to be used with swivel couplers).This is used in order to maintain

horizontal stability during concreting of the slab.

Upper screw jack (universal jack).

Steel base plates.

Mudsills (200X50) timber boards under the base plates on a pre-

stabilised pre-compacted levelled earth.

ii. Decking system consists of wooden and steel pieces as listed below:

o Main stringers: UAP100x50 steel sections.

o Steel form shaped to the slab soffit tailored exactly

o Secondary joists: Timber beams 100x50.

o Plywood sheets 1.22m x 2.44m x 12mm thick for the curved slab soffit supported longitudinally

on 100x50 timber joists spaced 200 mm. c/c.The timber joists are attached to a curved steel

section running in the transverse diction to form the required soffit shape. These sections are

spaced at 1300mm.

o Formwork levelling to be checked by contractor, to ensure providing levels as per bridge

alignment longitudinally and transversally prior to any installation of steel reinforcement.

4- GENERAL FORMWORK REQUIRMENTS.

o All formwork is designed to withstand the worst combination of total weight of formwork, reinforcement and concrete, together with construction loads including the effects of placing, compacting and construction traffic. The effects of wind loads are to be considered as appropriate.

o Formwork material is to be checked in advance to eliminate shortfalls and to ensure the required quality.

o All formwork erection is to be supervised by the contractor technical team to ensure:

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a) The form lining being used will provide the specified finish. Particular care must be exercised to ensure that the shutters are clean and oiled and do not contain unacceptable holes/repair work where the required finish prohibits this.

b) The position and type of ties when used are correct. All ties must be properly tightened to prevent distortion under load.

c) Where necessary, adjoining shutter boards are to be sealed to prevent grout loss.

d) Where shutters are clamped onto existing concrete, care must be taken to prevent grout loss or irregularities at the construction joint.

e) Release agents used must be suitable for any specified applied future finish.

f) The formwork has been erected so as to comply with the Project tolerances.

g) Cover blocks of the approved type have been securely wedged between the reinforcing and shutter to provide the specified cover and will not be dislodged under concrete vibration.

h) Safety regulations have been complied with and access is available for the concrete operations.

General Considerations:

Once the erected temporary formwork has been completed it will be checked by the site technical staff to verify acceptance. The Engineer will be required to inspect and approve the formwork.

Striking periods for formwork are to be agreed with the Engineer or as defined within the specifications.

C- STEEL REINFORCEMENT

Installation of steel reinforcement will be carried out exactly as per submitted and approved Shop Drawings.

Concrete spacers will be used to provide concrete cover for reinforcement. Reinforcing bars will be cut and bent on site. The reference is made to the following:

a) Bar Mark and Quantity.b) Drawing / Bending Schedule Reference Number.

Reinforcing steel shall be delivered to site and the foreman in charge will check the reinforcing bars to ensure correctness. Should there be any discrepancy then an appropriate action will be taken.

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FIXING

The steel fixing supervisor (foreman and sub-contractor) shall ensure that relevant current drawings are on site when fixing is in progress.

The steel fixing supervisor (foreman and sub-contractor) shall ensure that relevant current drawings are on site when fixing is in progress.

Only steel as specified on drawings and schedules shall be used.The foreman shall check all steel prior to completing the relevant portion of the pre-concrete Inspection form.

COVER

Cover to steel reinforcement as stated on the drawings will be insured using cover

blocks or plastic spacers as approved .

RECORDS

Records for inspection requests as required will be retained by the Project Manager /CICO & UEC for the duration of the contract.

D-CONCRETE WORKS Concrete Placement and Compaction

The aim of good concrete placing is to get the concrete into position at a speed, and in a condition, that allows proper compaction.

To ensure better rate of work, concrete is to be deposited at, or as close as possible to the exact spot where it is to be placed.

The deck slab will be cast in 2 stages :

The lower slab will be cast first taking into consideration the change in its thickness longitudinally and transversely in addition to the two longitudinal webs and parts of the top slab that surround the tendons.

The blisters will be cast completely in stage one.

The remaining parts of the top slab will be cast later.

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Vibration:

The Poker Vibrator

The poker or immersion vibrator is used for compacting concrete. It works directly in the concrete and can be moved around easily.

The time it takes for a poker vibrator to fully compact concrete depends on:

The workability of the concrete, the less workable the mix, the longer it is must be vibrated.

The energy put in by the vibrator, bigger vibrators do the job faster. The depth of the concrete, thicker sections take longer.

To realise the full potential of a poker, it is necessary to plan the compaction, along with the placing method and techniques well in advance, so that both operations are carried out as quickly and as economically as possible.

Below are some guides to ensure efficiency of vibration:

Make sure you can see the concrete surface – lights may be required in thin, deep sections.

Make sure the poker is inserted into the concrete quickly – as quickly as possible to reach the bottom of the layer it is compacting.

The poker should extend below the layer you are compacting and into the one underneath by at least 100mm – this will bond the two layers together.

The whole length of the poker should be in the concrete – this keeps the poker’s bearing cool.

Avoid leaving the poker running when it is not in the concrete, as this overheats the bearings.

A little extra vibration will reduce the number of blowholes – this is important when a good/smooth finish is required.

Clean the poker when you are finished. Pull the poker slowly as you withdraw it from the concrete – the object is to ensure that

no hole is left behind as the poker leaves the concrete. When you move the poker on, to compact the next section, it should not be far from its

previous position. Make sure the poker does not touch the formwork – the poker will cause a “poker-burn”

and mark the surface of the finished concrete.

Safety

Electrical poker cables must be protected and maintained by doing regular inspections. Pokers operated pneumatically (Petrol driven motors or air driven) shall be maintained and controlled as

with electric pokers.

Curing of Concrete

Curing is the last – and one of the most important stages of concrete construction

There are two basic methods of curing concrete.

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The first method involves keeping the surface of the concrete moist by the use of ponding, spraying/sprinkling, damp sand or damp burlap.

The second method is to prevent the loss of moisture from the concrete by covering it with plastic sheeting, spraying on a curing membrane, or leaving the formwork in place.

Plastic Sheeting (Polyethylene)

The plastic cover sheet should be placed in position as soon as possible – on vertical surfaces within half an hour of the removal of the formwork, on slabs as soon as the concrete is hard enough to prevent surface damage or marking.

It is important that the exposed edges and corners of the sheet should be well fixed down, to prevent wind tunnels that could affect the curing process.

Spray-On Curing Compounds

Curing compounds are sprayed onto the surface – a hand-held garden spray is suitable for most jobs – and can be used on both vertical and horizontal surfaces.

If a curing compound is to be used, approval must be obtained from the client and that particular compound manufacturer’s instructions to be strictly followed.

Time to spray:

The compounds should never be applied to dry surfaces since these will absorb the compound, and staining or discoloration may occur. If the surface is dry, that is a sign that the curing has been left too late.

On vertical or sliding surfaces, apply the compound almost immediately after the formwork has been struck, or move during the slide.

Protection given by formwork

While it is in position, formwork protects concrete against loss of moisture, and thus allows curing to proceed. It is only after it has been struck that further curing of columns, walls and beams may be necessary.

The colour of concrete can vary according to how long the formwork is left in position after placement, and whether the day on which it is struck, is dry or wet.

Attachments:

1- Design calculations for the column formwork.2- Design calculations and layout of the bridge slab decking and propping system.

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viaduct 2 final method statment

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