Assessment of Khilgaon flyover under seismic load

Abstract

The 1900-meter long multi-span Khilgaon Flyover comprises three mam arms namely Rajarbagh, Saidabad and Malibagh anns forming aT-junction at Khilgaon road and rail intersection and a loop at Malibagh portion of the bridge. There are ramps at ends of all the three anns. The sub soil strata of the site is composed of Dhaka clay and is not susceptible to liquefaction under a moderate earthquake. However, recent earthquakes like Asia-Tsunami (2004) and Kashmir Earthquake (2005) make experts think that Bangladesh may experience a severe earthquake at any time. For this reason a structure need to be designed considering a probable earthquake and re-evaluation of existing structures is necessary. Since most part of the flyover is simply supported, in this study seismic response of a single typical 26 m long span and a bored cast in situ RC pile under a typical pier were investigated. Both static and dynamic linear analyses were perfomled. A typical span comprises of RC deck resting on PC girder which ultimately transmits loads through single RC pier cap and pier system to cast in situ RC pile foundation. Superstructure and substructure were analyzed separately. Main objective of this study was to investigate the behavior of the flyover under seismic forces. For static analysis Single Mode Spectral Analysis Method as specified in AASHTO (1996) was adopted. In linear dynamic analysis, UBC (1994) response spectrum was used as input acceleration. Finite element software SAP2000 was used as a tool for 3D analysis of the superstructure as well as the substructure. Structural responses, i.e. mode shapes, pier top deflection, pier base forces, pile top deflection, forces at pile etc. were observed and estimated. It is observed that static analysis produces slightly conservative values than dynamic analysis. In both cases, structure was found to be safe.