Vasudev V Nori, Shirish Patel and Associates Consultants Private Limited (India)
Concrete bridges are often simply supported structures with bearings and expansion joints. Like elsewhere in the world much of the observed distress in these bridges emanates from expansion joints and bearings. This paper deals with evolution of precast concrete bridges with monolithic piers which need very little maintenance. The structures described have proved to be both elegant, efficient and maintenance free compared to traditional cast-in-situ structures.
Simply supported girders resting on bearings are still very popular. The main reason for their popularity is that these structures are simple to design and to execute. The substructure design is also greatly simplified because of determinate nature of the structure. On the other hand most of the distress observed in bridges constructed during the last fifty years emanates from the expansion joints and bearings. Unsatisfactory performance of expansion joints results in ingress of rain water through the joints and causing damage both to the structure and to the bearings. It became necessary to detail these joints so that adequate space is available for maintenance and replacement. During earthquakes it has been found that spans get dislodged from bearings at times. Indian Road Congress Codes require that positive measures such as restrainers be provided for bridge structures in Zone IV and Zone V so that the deck does not get dislodged during earthquakes.
It is true that there are situations where bearings and expansion joints cannot be altogether avoided. On the other hand monolithic construction and redundancy of the structural system do result in savings in the cost of construction and maintenance. Elimination of bearings improves the structural performance during earthquakes. Finally integral form of construction will require much lesser inspection and maintenance efforts.
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