DYNAMICS OF SEISMIC POUNDING AT EXPANSION JOINTS OF CONCRETE BRIDGES

Motivated by a need to understand the effects of earthquake-induced po unding at thermal expansion joints of concrete bridges, the first part of this paper deals with collinear impact between concrete rods of th e same cross section but different lengths. It is shown that (1) the c oefficient of restitution between rods depends only on the length rati o and the damping ratio of the rod material; and (2) the duration of i mpact is equal to the fundamental period of axial vibration of the sho rter rod. These results are then used in the second part of this paper to formulate a realistic yet simple analysis of seismic pounding in c oncrete bridges. In determining a suitable value of the coefficient of restitution, use is made of the strong-motion data recorded on a conc rete bridge that experienced significant pounding during recent Califo rnia earthquakes. It is shown that (1) seismic pounding generally redu ces the column forces; (2) large impact forces generated in the supers tructure are not transmitted to the bridge columns and foundations; an d (3) pounding does not increase the longitudinal separation at the hi nges.