Bridge at Bhagalpur

8/13/2019 Bridge at Bhagalpur

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Bridge at Bhagalpur


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INTRODUCTION

The Chinese and Indian construction industries are the largest and second largest in theworld. Engineers in these countries have had the opportunity to engineer major civilengineering projects for their countries. The cost of labour against materials, in a typicalconstruction project in these countries, is similar to what existed in Europe a century ago.In the US or Japan special construction techniques have to be developed to suit theconstruction environment of these countries. At the same time, the most advancedtechniques in the world are used, in view of the large number of major projects to be carriedout in the developing countries.

The bridge at Bhagalpur across the river Ganga having a length of 4.37 km and is the

second longest road bridge in India. This project has been engineered to suit the

South Asian construction environment


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The bridge at Bhagalpur across the river Ganga - the second longest inIndia - has a length of 4.37 km. The bridge has four types of structures

corresponding to the 4 regimes of the river.

1. Zone A

2. Zone B

3. Zone C,&

4. Zone D

Bridge at Bhagalpur

PARVATIKATTABRIDGE


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The Zone' A', across the deepest part of the river, Span- 120 m , Total length of 1104 m constructed over standing water, which at low water

level has a maximum depth of 7 m over the riverbed. The superstructure is supported on hollow RC piers erected on 9 cylindrical RC well

foundations which were to be sunk from sand islands - 7 m deep - by excavating soil fromwithin the wells by grabs.

The prestressed concrete superstructure consists of cantilevers of 48 m length, fixed tothe pier and a 24-m long RC suspended span across the cantilever tips, to give effectively8 spans of 120 m, at centre of piers, and approach spans of 72 m, at centre of piers, oneither side.

The nextZone 'B' , Which is 1139.4 m long, is normally dry, and is covered with water only during floods.

This zone has well foundations which are sunk from the highest bed level up to a depth of70 m.

The superstructure is made up of simply supported box girders having a length of 63.3 m,

resting on hollow RC piers.

STRUCTURALDETAILS


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STRUCTURALDETAILS

Zone 'C',Fig 3, which has an aggregate length of 1961.80 m is constructed in a zonebeyond the left bank (at the end of zone B) to cross the backwaters which occur during highfloods. It consists of wells sunk upto 60 m below the highest ground level in this area.

Zone 'D',Fig 2, is the approach viaduct zone and

has five simply supported box girder spans of 32.4 m (with a total length of 162 m)constructed on staging,

are founded on shallow cylindrical RC well foundations sunk 18-m deep below the

highest riverbed in this zone.


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During high floods the river is expected to scour below high flood level (HFL) to a depth of 47m in zone A and B, and 40 m in zone C. Therefore the wells go down by an additional depth of22 m in zones A and B, and 16 m in zone C, in order to provide a sufficient grip length toresist the horizontal forces due to high floods as well as earthquake and wind effects.

STRUCTURALDETAILS

Fig. 4

In Zone A, Fig 4, the depth of the superstructure

at the pier is 9.6 m and at the cantilever tip it is

1.95 m, which are 1/11 and 1/62 of the span-

depth to span ratios which minimize on

materials consumed.

The prestressed cantilever portion of the deck is

constructed by the free cantilevering method

with cast-insitu segments.

The webs for a height of 9.6 m are only 37 cm in

thickness. The longitudinal prestressing cablesare placed in the top slab so that the web is free

of prestressing cables and can be concreted by

form and pin vibration - with a succession of

windows within the height of the web to facilitate

pin vibration and observation of compaction of

concrete during placement.


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Fig 6 shows the lifting by prestressingcables of temporary steel decks used forcasting the 24-m long RC central span.

The superstructure of zone 'B', Fig 7, iscast in-situ on scaffolding supported onthe dry riverbed. The piers have hollowconical sections which flare out at thetop into a hammerhead in order tosupport the span on either side. Thepiers also flare out at the bottom to restconcentrically on the walls of the wellfoundation (when there is no tilt andshift of the foundation).

STRUCTURALDETAILS

Fig. 5

Fig. 6

Fig. 7

In zone A, Fig 5, the piers have a hollow circular section

which flares into a hollow square section at the junction of

the superstructure. The pier and the deepened deck seem

to flow into each other - an aesthetic consequence of a

search for dematerialization.


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At this site, the maximum shift recorded was 186 cm.There can also be unseasonal floods due to the earlymelting of Himalayan snows and the wells can tilt andshift during the sinking process. During suchunexpected floods, wells that were not yet sunkadequately toppled over. The scoured level could also

become much deeper after a flood than that recorded byinvestigations at the beginning of the project. In thiscase during heavy unseasonal floods, two wells toppledover. A part of the bed which had been scoured did notget re-filled due to the flash floods which occurred. Thedepth of standing water became 22 m instead of thenormal maximum depth of 7 m at low water level. In thecase of those wells which tilted excessively, additionalfoundations were cast. The wells in this portion were

cast by sinking hollow steel caissons, Fig 10.

STRUCTURALDETAILS

Fig. 8

Fig. 10

Fig. 9

The casting of the box girders on scaffolding, resting on the

dry river bed, was cheaper than precasting and launching ofentire spans, Fig 8.

The construction of the piers and foundations in zone C wassimilar to that shown in zone B, Fig 9.


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The hollow space between the inner and outer walls of the caissons had a thickness

equal to the lower part of the RC well steining. It was constructed using catamaranbarges and the sinking technique utilized for the cofferdams was the same as that forThane Creek Bridge, except that concrete was poured into the hollow caisson wall tofacilitate the lowering of the same till it touched the river bed; verticality was maintainedby the prestressing cables which were used for lowering the caisson. Thereafter theconstruction was completed by the traditional sinking process utilized for all the otherwell foundations.

The only regret was that the TOR of the turnkey bid did not permit either segmentalprecast cantilever construction or a cable stayed solution. All the pier locations werealready fixed and therefore the design of this bridge could not be optimized to themaximum. However, building a great bridge is always satisfying to all concerned

Construction - V.P. State Bridge Corporation,

Design - STVP Consultants Pvt. Ltd and construction engineering and providedconstruction assistance

STRUCTURALDETAILS

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Bridge at Bhagalpur