DYNAMIC ANALYSIS OF DECK TYPE STEEL ARCH BRIDGES

Abstract

Arch bridges are one of the oldest types of bridges having great natural strength. The curved structure of an arch bridge gives high tolerance for bending. Dynamic analyses of bridges and their response become foremost important for their structural safety where bridges are situated in an earthquake prone as well as strategic location over a deep valley and also where wind velocity varies abruptly. For the critical condition, it would be difficult to control transverse displacements due to wind and earthquake in any other type of bridges. In this situation trussed arch bridge is most preferable solution and aesthetically pleasing. In this study, dynamic analyses of deck type steel arch bridges of span 100 m, 150 m, 200 m, 250 m, and 300 m have been carried out and their responses under different load combinations and boundary conditions of deck girder are presented herein. Bridges have been considered as a deck type trussed arch with steel boxes consisting of different cross sectional area for arch rib and I sections for stiffening deck to arrive at feasible structural system. Time periods and mode shapes for all the five bridges with three types of boundary conditions for deck girder are presented. IS code response spectra for DBE and MCE conditions for seismic zone V (Type-I, hard soil) have been used to obtain the response. Further, the response of all the five bridges have also been obtained for site dependent response spectra for Anjikhad and Chenab sites under both DBE and MCE conditions. Wind pressures have been calculated for normal as well as reduced wind speed and analyses have been carried out accordingly. It is observed that the forces for combined dead load and earthquake load are smaller as compared to dead load and half live load. Therefore the combination of dead load and half span live load condition is most critical condition. The vertical and transverse deflections of all the five bridges are observed to be within permissible limits. Typical members of 300 m span bridge have been designed and found to be safe. Further, the stresses are also within permissible limits.