Segmental construction of Bridges

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INTRODUCTION What is Segmental Bridge Construction ? In contrast to classical monolithic structures a segmental bridge consists of “small” Pieces stressed together by external tendons. Segmental construction is gaining popularity as a method of construction where the local terrain and/or traffic prohibit the erection of conventional false work .

Why go for Segmental Construction? :

Why go for Segmental Construction? Segmental construction technique, facilitates construction of longer span bridges, reduces intermediate piers and thus obstruction to flow and avoid system of erection of staging from river bed level, and has been a very effective and economical technique in such situations.

History :

History This method of const. first developed in western Europe particularly in France & Germany during 1950’s. Over 70 bridges of this type under const. during 1971-75 in France. In India during 1960-61,@ 250m long Barak bridge was constructed.


CONSTRUCTION TECHNIQUES Delicate process & needs fine balance Any Imbalance leads to damages, so needs careful & systematic approach in casting of segments. For that proper flow chart of the activities & sequence there for to drawn. Launching & const. sequence differ according to con. tech, & its depends on the con. site, geological studies etc. The techniques can broadly be classified as under: Cantilever Method for Cast-in-situ Construction Incremental Launching Method. Construction with Precast Segments.

Cantilever Method for Cast-in-situ Construction :

Cantilever Method for Cast-in-situ Construction CONSTRUCTION METHODOLOGY Pier head is casted with detailed planning A steel gantry then designed & fabricated. Thereafter, soffit shuttering, shuttering for web & deck shuttering is fixed to the overhanging portion of the gantry on both sides. Reinforcement is then tied as per drawing. Then concreting is done on both sides of the gantry. Photo1: Construction of initial unit

Cantilever Method for Cast-in-situ Construction:

Cantilever Method for Cast-in-situ Construction General Schedule Construction of one unit each on both sides of pier head - 7 days . Erection of gantry - 10 days. Casting of each subsequent cantilever units (including prestressing of cables to be anchored at that units) - 7 days Special Consideration During Construction Segment need properly anchor with pier cap during whole const.

Precast Segmental Bridge Construction using Launching Truss :

Precast Segmental Bridge Construction using Launching Truss It is economical for large project, due to investment req. for casting, handling & erection of precast segments. The construction of a flyover in an urban environment is not always welcomed by the society because of traffic disturbance & construction delays, nuisance caused during concreting & erecting the formwork at site and noise & visual pollution.

Construction Methodology:

Construction Methodology Segments are casted in the casting yard. launching girder is used for erection of precast segments. The launching girder has two parallel triangular trusses provided with hangers to hold the segments during erection.

Design Steps :

Design Steps Finalization of the dimension of box girder depending upon the width of the carriageway/ footpath. Depth at root section however mainly depends upon the span length and is normally equal to 1/8 of span. Based on the length of the arm, it is then divided into likely construction units. Length of each unit is generally kept in the range of 3.0 m to 4.0 m based on the construction convenience and gantry parameters.


CASE STUDY Ganga bridge at Buxar- This balanced cantilever bridge is situated in Bihar on an important highway link on Ganga river . Span-1122.26 m. No. of span- 12. 10 intermediate spans of 101.22m & two end spans of 55.03m . Out of 12 T-arms, central 10 T-arms, were constructed using Precast segments & one each on either bank was insitu . The weight of Precast segments was varying between 2.13m near pier to 3m for the balance portion.


CONCLUSION With the introduction of in-situ segmental construction the problem of constructing longer span over rivers, creeks as well as gorges was successfully overcome. Precast prestressed segmental construction is a versatile technique for construction of present day fast track jobs. Segments can be cast away from actual site, their by minimizing hindrance to traffic & public in urban environment. In casting yard better control on quality & dimensional tolerances can be achieved. Segment casting can start independently as work on foundations progresses, their by reducing overall completion time.

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