EARTHQUAKE RESPONSE OF CABLE STAYED BRIDGE ON ALLUVIAL SOIL

Abstract

The cable stayed bridges have proven to be economical for medium to long spans. It fills the void between conventional short and long span suspension bridges. The most striking feature of such bridges, apart from technical features, is their elegant form and adaptability to a wide variety of practical situations Cable stayed bridges possess low weight and reduced ability to absorb energy by sliding friction. So th-- inertia force generated in structure is very low in comparison to external loads. As the cable stayed bridge has complicated vibrational, systems due to different structural properties, it is Important to carry out elaborate dynamic analys'.s for determining the distribution of forces caused in the various elements of the bridge. In the present study dynamic analysis of 130 in cable stayed bridge at Hardwar has been carried out. The dynamic analysis has been carried out on the basis of plane frame idealization of the structure The earthquake response of this bridge have been analysis for various parameters such as ; variation in soil condition, shape of response spectrum and snapping of cables. In order to study the effect of response of tower It self on the bridge, the time period of tower has been found out in both longitudinal and transverse. direction. All the response spectra are normalised such that they have the zero period acceleration of IS code spectra. vi From the analysis, it has been observed that shape of response spectrum does not produce any change in earthquake response such as ; shear force, bending moment in sub structure and tower. However, in girder the displacement, shear force and bending moment for spectra of soft soil is considerably more than medium and hard soil. The IS code spectra gives lower value of response in sub structure than spectra for hard, medium and soft soil. Soft soil causes more shear force, bending moment and displacement in superstructure than medium and soft soil. But for substructure the case is reverse. Snapping of cables does not produce any change in response. The time period of tower Is more-" longitudinal direction than in transverse direction. The axial forces generated in cables is very less as compared to pretension force. So there is no possibility of slacking of cables.