EFFECT OF SUBSTRUCTURE CONFIGURATION ON SEISMIC PERFORMANCE OF A BRIDGE

Abstract

Bridges are playing a very important role in transportation systems. These types of life-line structures have to be designed that they continue to serve during earthquakes.The performance of bridges under greater earthquakes can be depending on their energy dissipation capacity. In buildings weak beam strong column philosophy is adopted for energy dissipation but in the case of bridges piers are designed to bear the damage and plastic hinges are formed in abutment and pier or only in piers for representing elastic energy dissipation. Behavior of bridge during earthquakes depends upon bridge type and substructure configuration. If the substructure configuration varies significantly along longitudinal direction, stiffness of each span changes drastically. Single column bent, multicolumn bent and linked columns are most common type of substructure configurations. This study is focused on behavior of bridge with different types of substructure configurations under earthquake conditions. In this study various advantages and disadvantages of different kinds of substructure configurations is discussed. Performance of bridges with different types of substructure configurations during past earthquakes is presented. Modelling of the superstructure and different types of substructure configurations is addressed in the present study. Modelling of structural materials like concrete models and steel models are discussed. A brief description about nonlinear static and dynamic analysis is presented. For this study a simply supported truss superstructure of existing railway bridge with different substructure configurations is considered.ln order to study the effect of response reduction lictors, bridge piers are designed and analyzed for different values of response reduction factors. Along with single column bent configuration, multicolumn bent configuration and linked type column configuration are considered for study. Nonlinear static pushover analysis is performed for all bridge models with different substructure configurations to find the yield strength, yield displacement and ductility capacity and performance of the bridge with respect to collapse margin ratios. Irom the results of nonlinear pushover analysis it is concluded that linked columns have better performance than other type of substructure configurations. In addition to nonlinear static analysis nonlinear dynamic analysis is also performed on all three types of configurations using the method prescribed in FEMA-P695 document. IDA method has recommended for doing nonlinear dynamic analysis in that document. Collapse margin ratio is calculated from the results of nonlinear dynamic analysis. Adequacy of the response reduction factors for different types of response reduction factors is checked using the collapse margin ratios. It is found that response reduction factors given in IITK-guidelines are giving satisfactory results for linked columns whereas for multi column bent configuration and single column bent it has to be revised as per FEMA-P695.