FULL SPAN BOX GIRDER CONSTRUCTION

 

BOX GIRDER CONSTRUCTION

          Machineries

Mobile Crane		1 No
Concrete Pump		As required
Transit mixers		As required
Vibrators with Shafts		8 Nos
50 KVA Power generator		1 No
1 HP Water Pump		2 Nos
250 cfm Air Compressor		1 No
Phneumatic wrinch		1 set
Post tensioning equipments Grouting equipments		1 full set        1 full set              “

       Ground preparation

Existing ground shall be leveled and compacted upto design RL for receiving the staging system.

Bearing capacity of the soil shall be checked and confirmed.

        Erection of Staging system

§  This staging system is specially designed and fabricated for the capacity

§  Design calculation for the system shall be submitted for approval.

§  Marking of system legs on ground shall be done and specially made concrete blocks shall be placed accordingly and inline & level.

§  The concrete block shall be designed and cast at site for the work.

§  Over the erected blocks pre-assembled system towers shall be erected as shown in the sketch.

§  On erected towers ‘ I ’beam  shall be placed as primary beam in transverse direction of bridge alignment.

H.20 Timber beams shall be placed over the primary beam as secondary beam of platform and as per dimensions and spacing shown in sketch.

Main Staging shall be completed as per sketch. 

Access to main staging shall be done with ordinary cup and lock scaffolding and aluminium ladders in 4 different locations.

Setting out survey

One Total Station with other accessories shall be used to do the layout of soffit shuttering.

Soffit shuttering levels shall be checked and recorded.

Web layout shall be marked on soffit shuttering. 

Bearing erection

Bearing erections shall be done in locations of pier column and abutments as per the locations marked already in line and in level.

Bearing shall be grouted with approved non-shrink grout and cured.

Form Work

Soffit of bottom slab shall be done with 18mm thick marine grade shuttering plywood fixed on H-20 secondary beams inline and level.

For adjusting and maintaining the levels of soffit shuttering the screw jacks on top of staging shall be used and completed.

External web shall be marked on soffit shutter and specially made external side shutters shall be fixed in line and in level.

External side web shutters shall be fabricated specially for the work at site with 18mm thick commercial plywood; 4”x3” red wood battons  and 6.5mm thick marine grade plywood as shown in sketches.

All other form work shall be made with 18mm marine grade shuttering ply and 4” x 3” timber.

Internal web marking also shall be done on the soffit form work.

Access doors shall be installed as detailed on the drawing.

Reinforcement fixing shall be done for bottom slab.

PVC vent pipes shall be fixed in cells as indicated in drawings.

Special formwork shall be done on bearing locations.

Reinforcement fixing shall be done for bottom slab, diaphragm over pier, beam over abutment and web etc.

Web side shutter and diaphragm shutter shall be done as shown in sketch.

All the shuttering works shall be done with 18mm marine grade plywood and 3”x 4” wooden battens.

Tie rods shall be provided for keeping the shuttering in position and arresting the pressure on shutters during concreting.

The tie rod holes shall be filled with non  shrink grout.

Reinforcement fixing 

All reinforcement bars shall be of the deformed High yield steel bars grade 460 type 2 in accordance with B.S 4449,1997 and shall be from Sharq Steel Sohar

All the reinforcement layout shall be done over soffit shuttering for Base slab Web and diaphragms. 

The cut and bend reinforcement fixing for the diaphragms over pier, beams over abutment bottom slab, web etc. shall be done as per the approved BBS & drawing.

The bottom layer of bottom slab reinforcement shall be fixed in position as per drawing

Reinforcement for Webs shall be fixed in line as per drawing and as per approved bar bending schedule.

Top layer of the bottom slab reinforcement fixing shall be done.

Ducts for the Post tensioning system shall be marked on the web reinforcement in profile and levels as per the drawing. 

Duct inserting and fixing in positions shall be done with extra care and as shown in drawing.

Fixing of P.T Duct, Tendon, Tensioning, Grouting etc; separate methodology shall be submitted.

After fixing the P.T. Duct the web shuttering shall be completed as shown in the sketch.

Wooden mandrills, driven by ropes shall be kept inside the P.T Duct for ensuing the duct is clean and empty during concreting.

These mandrills shall be operated forward and backward by pulling the ropes fixed to that to clean the duct during concreting.

The same ropes shall be used to guide the tendon; during treading into duct.

During and after, the activities shall be inspected jointly and recorded.

Concreting

Box girder concreting shall be done in 2 stages as shown in sketch.

1.      Soffit and Web.

2.      Deck slab

 1)     1^st stage – soffit and web.

Vertical construction joints shall be provided in the middle span ( 0.20 of the span ) i.e 8.40 mtrs from pier as shown in sketch.

Special care shall be taken in the surface finishes during concreting.

This stage shall be done in 3 pour sequences as shown in sketch.

1.  Concrete shall be placed through web and vibrated till a level achieves upto the web kicker.

2.  Slab portion shall be concreted.

3.  Web portion shall be completed.

 All these pour sequence shall be done in such a way without any cold & joint. 

After 36 Hrs web shutter shall be removed and lowered down for the II nd stage concreting

 

II Stage – Deck  Slab

The scaffolding arrangements for the deck slab shall be done and reinforcement for deck slab also shall be fixed .

The reinforcement shall be inspected and recorded jointly.

Concreting for the deck slab also shall be done as first web portion after that slab portion

Curing

Wet hessain cloth and PVC sheets shall be spreaded over the concrete immediately after the finishing and water shall be sprinkled over.

After the final set of concrete water pouring shall be done to keep the hessain cloth always wet.

Post tensioning of Girder 

Separate method statement shall be submitted.

Post tensioning of concrete shall be done as soon as the concrete attained a strength of 80% ie. 36 N/mm² for the last placed concrete.

2 Nos or more cubes shall be tested to find out the strength of concrete and recorded.

 20 mm dia Air Vent pipe shall be fixed at the highest point of level to release air and confirming the grouting work.

Safety

Maintaining proper access to work area.

All lifting equipments and accessories shall be certified for their capacity and integrity

Proper barricading shall be done around foundation

Sign boards shall be erected.

Material and components use d for the work shall be examined for damage or excessive deterioration before use and if found unsuitable shall be repaired or scrapped.

Explaining the direct or hidden hazards for the activity .

Maintain good house keeping at site.

Ensuring all PPE and safety related materials are used.