Structural performance of some existing bridges of Bangladesh under earthquake load

Abstract

Seismic design provisions of AASHTO codes are usually used for designing bridges in Bangladesh. Both dynamic and equivalent static methods of analysis are recommended in AASHTO code. In Bangladesh, the static analysis is mainly followed. A structure may behave either elastically or plastically under earthquake load depending on its intensity. However, the structure is allowed to behave nonlinearly under the design level of earthquake but the performance of the structures incorporating this nonlinearity are not evaluated during the static design procedure. It is, therefore, necessary to have a clear understanding of structural response under earthquake force following a method popularly known as perf0l111anCeevaluation. Elasto-plastic response of three important existing bridges under seismic load has been evaluated in this study. Before can'ying out the task, existing literatures on relevant field is thoroughly reviewcd. Elasto-plastic analysis has been conducted following performance based design method. The performance level of the structure under different load intensities are detennined. Here, a perfonnance level means the damage level, which can be assessed and judged. Three bridges from three different seismic zones of Bangladesh are selected for study. Non-linear static pushover analysis are perfonned for these stmctures to cvaluate its performance under seismic load. The analysis has been can.ied out following guide lines of Applied Technology Council (ATC ) and Federal Emergency Management Agency (FEMA). Capacity Spectrum method has been employed to detel111ine the performance levels. One of the study bridge located near Sylhet town meet Life Safety Perfol111ance Level in its longitudinal direction and Damage Control Perfot111ance Level in transverse direction. At this perfonnance level, severe damage of the bridge without collapse could be expected under design level of earthquake. The other two bridges located near Barisal town and Dhaka city meet Immediate Occupancy Performance Level. In the Immediate Occupancy Perfonnance Level, only minor repairable cracks may develop.