NON LINEAR ANALYSIS OF BRIDGES FOR SEISMIC LOADING

Abstract

Literature has been reviewed from proceedings of world conference on earthquake engineering as well as various journal papers, of past several years. It has been noted that bridges failed due to unseating of superstructure due to pounding or failure of bearings besides failure of piers in flexure or shear. It is essential to carry out non-linear modeling of the bridge in order to study the seismic response of a bridge/viaduct. A stick model was used to simulate 3 span simply supported viaduct using SAP2000 with due consideration of impact and separation, the pounding between the adjacent spans and cyclic yielding of materials. Discrete zero-length spring elements are used to model bearings. Pounding effect is modeled using a compression only gap element. The non linear behavior of reinforced concrete pier is represented by a hysteresis fiber model. The geometric nonlinearity of RC pier due to P-z\ effect is also considered. The pounding has significant effects on displacement and axial forces of decks. In order to control pounding and displacement at top of the pier, viscous dampers have been used in the model. It has been studied by modeling a separate stick model including viscous damper, to study the effect of viscous damper on the response of the bridge. It has been found that 75% of moments of pier were reduced by use of viscous damper where as pounding had been completely controlled leading to zero impact force at the superstructure deck of the bridge. Simplified model as used by DesRoches and Muthukumar (2002) has been used to compare the results obtained from stick model. Response of bridge due to pounding and Top pier drift have been studied using simplified model and stick model. Results revealed that there was average difference of about 5% to 8% between results obtained from both the models. Further, Simplified model has been used to fmd out impact forces for various spans of the bridges with different superstructure and substructure configurations. Charts have been suggested so as to give an idea regarding impact force generated due to pounding of superstructure of the bridges under consideration. iii