Dynamics of Seismic Pounding at Expansion Joints of Concrete Bridges

Abstract

Motivated by a need to understand the effects of earthquake-induced pounding at thermal expansion joints of concrete bridges, the first part of this paper deals with collinear impact between concrete rods of the same cross section but different lengths. It is shown that (1) the coefficient of restitution between rods depends only on the length ratio and the damping ratio of the rod material; and (2) the duration of impact is equal to the fundamental period of axial vibration of the shorter rod. These results are then used in the second part of this paper to formulate a realistic yet simple analysis of seismic pounding in concrete bridges. In determining a suitable value of the coefficient of restitution, use is made of the strong-motion data recorded on a concrete bridge that experienced significant pounding during recent California earthquakes. It is shown that (1) seismic pounding generally reduces the column forces; (2) large impact forces generated in the superstructure are not transmitted to the bridge columns and foundations; and (3) pounding does not increase the longitudinal separation at the hinges.