Simplified seismic analysis of a class of regular steel bridges

Abstract

AASHTO’s (American Association State Highway and Transportation Officials) simplified method of analysis for multiple-span regular bridges requires modeling and analysis of the structures and it is not less time-consuming than performing a computer-aided response spectrum analysis. Furthermore, for single-span bridges, AASHTO specifications do not require a seismic analysis. The connections between the superstructure and substructure are designed for a minimum load calculated as the product of site coefficient, the acceleration coefficient and the tributary permanent load. This may result in underestimation of seismically induced forces in connections. To overcome such problems, analytical equations are derived to calculate the fundamental period and seismically induced forces and displacements in the structural components of a class of regular steel bridges. The equations are derived considering the effect of deck width, number and length of spans, bearing types and their stiffness, on the dynamic behavior of bridges. The results from multi-mode response spectrum analysis and those obtained from the derived equations have shown good agreement. Thus, these equations may be used in lieu of AASHTO’s simplified analysis method for the seismic analysis of regular steel bridges. It was also observed that AASHTO’s simplified analysis method for single-span bridges underestimates the seismically induced forces in fixed bearings.