SESIMIC ASSESSMENT OF CONTINUOUS BOXGIROER BRIDGE WITH TALL PIERS

Abstract

The overall response behavior of highway bridges under both service and seismic loads is inherently complex. Therefore, there is continuing research on methods that properly capture the effects due to the seismic effects. This study examines the seismic response of a three-span continuous concrete box girder bridge. Bridge taken for this study is a railway bridge located in a valley on Jammu Udampur Rail-Link with two middle piers as tall piers. 3-D finite element model is used to assess the seismic performance of the bridge. Thin shell elements having 6 DOF is used for modelling deck and piers are modeled with beam elements having 6 DOF at each node. The base of intermediate and end piers is assumed to be fixed. Both material nonlinearity and geometrical nonlinearity is been incorporated in the model by using stress-strain curves and P — A effects respectively. Material non-linearity is assigned to frame elements in the form of hinges. The response spectrum and linear time history analysis has been done using design response spectrum given in IS 1893:2002 and the time history compatible to the response spectrum. Shear forces and bending moments at base are compared for both the cases and they are found to be close enough. Further pushover analysis has been done in both longitudinal and transverse direction by applying the load patterns defined as per FEMA 356 to get the performance point in both capacity spectrum method and displacement coefficient method. Nonlinear time history analysis has been done for design based earthquake and maximum considered earthquake ground accelerations to get the realistic performance. Shear forces, bending moments and displacements of nonlinear time history has been compared with pushover analysis. From the results it was observed that shear capacity of structure is less than demand got from NL-THA. The performance points were observed in pushover analysis by two applied load cases. Maximum values of shear capacity and displacement from two load cases are close to the response of NL-THA.