Paper Bridge Construction Method

Paper Bridge Construction Method

“BALANCED CANTILEVER CONSTRUCTION OF PSC BRIDGE” CAST-IN- SITU CONTINUOUS UNIT

Balanced cantilever construction implies construction of cantilever segments from a pier in a balanced fashion on each side until the mid span is reached and a closure known as stitch segment is made with other half span cantilever constructed from the preceding pier. The process :  The form work is suspended from the end of the last segment.  The new segment is cast and once the concrete has developed a predetermined strength, the section is post tensioned to the rest of the bridge.  The same erection process is repeated till the structure is completed.

Construction Sequence

Fundamentals of Design  Building a bridge deck by succession of segments where each segment carries the weight of the next segment  Each segment is integrated with the previous one as soon as it is strong enough.  Each segment becomes self supporting and also becomes a base for a new segment.

 The stability of cantilever is secured at each step by pre-stressing cables provided in the upper fiber - In order to avoid asymmetric overturning moments, the construction is done symmetrically on the pier on both the sides.

Necessity of Cast-In-Situ Construction  When access below the bridge is expensive or practically impossible due to busy road, river, canal, deep valley or railway track etc.  Longer span (where launching is very costly).

Construction Over Busy Road

Segmental Construction Over Railway Track

DMRC Cast in place balanced cantilever

Segmental Construction In Progress Over A River/ Sea

CONSTRUCTION MACHINERY 1. Batching Plant. 2. Transit Mixers. 3. Concrete Pump. 4. Welding Generator.

5. Concrete Vibrators. 6. Concrete Needles.(6o&25mm dia). 7. Compressor. 8. tyre mounted crane. 9. hand winch. 10. chain pulley block. 11. pipe wrench. 12. clc gantries (80t)-4nos. 13. grout pump.

Figur : Concrete Pump

Figur : Bridge Builder

Critical Construction Materials 1. Pot-ptfe bearings 2. Anchorages-19k15,and grips. 3. Bearing plates. 4. Ht strands (is-14268 class-2) 5. Gi sheathing pipes-id 110mm. 6. Cement opc 53 grade 7. Reinforcement steel is-1786 8. Admixture is-9103

Operation Sequences 1. Survey work: center line marking for foundation of trestles will be done with the help of theodolite/ total station. 2.Construction of pier head: (a). Trestle fabrication and erection for

construction of pier head.

(b). Design and fixing of bearings. (c). Super structure stabilizing arrangements: the additional trestle and sand jacks of 350 tonne capacity are placed at required locations.

Figur : Operation Sequences

(d). Calculation of co-ordinates for horizontal curve and deck level for vertical curve. (e). Soffit, web external and deck shuttering. (f). Soffit, web and deck reinforcement. (g). Cable profiling. (h). Embedded fixtures. (i). End stopper shuttering. (j). Concreting with concrete pump. (k). Curing is done for 14 days. (l). Hydro testing of sheathing pipe at 0.3 mpa pressure. (m). Prestressing and grouting: stressing starts only if concrete attains the desired compressive strength.

3.Construction of Cantilever: (a). Fabrication and erection of clc gantries (bridge builders)(2+2=4sets).

(b). Pre-camber calculation. (c). Gantry alignment and level. (d). Soffit shuttering. (e). External shuttering. (f). Reinforcement, sheathing pipe and cable profiling. (g). Internal shuttering of clc gantry is moved on mono rails and fixed to the location as per drg. (h). End stopper shuttering. (i). Applying adhesive (nito bond etc.) On face of old concrete. (j). Concreting of 3m long segments on either side of pier head simultaneously or one by one using concrete pump. (k). Curing. (l). Pre stressing and grouting. (m). Releasing of clc gantry form work. (n). Movement of clc gantry (bridge builder.) for shifting to next unit. (o). Levelling and alignment of clc gantries. (p). Similar procedure to be adopted for other segments.

4.Construction of End Span. (a) casting of end span is done after the cantilever construction. activities involved remains the same as explained for pier head construction. 5.Casting of Stitch Segment (a) after casting of clc span, the remaining portion of length 2.50m segment is to be stitched.

Safety Precautions 1. load test of crane should be done by third party. 2. working platform and safety nets will be provided.

3. safe access by means of ladder will be provided from ground to deck top. 4. the macalloy bar is designed for fos =3. 5. all electrical connections should be proper. 6. temporary hand rail will be fitted for deck slab casting. 7. fall arrester should be provided. 8. height gauges and caution boards should be fixed for road users. 9. proper personal equipments (ppe) like safety helmets, safety shoes, safety belts and safety nets shall be used.

Figur : Hight Gauge for Road User

Figur : Safety net