Studies on the effect of differential motions of two foundations upon the response of the superstructure of a bridge

Abstract

This report contains two studies that were made of the effects of differential motion of the foundations upon the response of the super structure of a bridge. The first study deals with the dynamic response of a "1ong beam" model of a bridge to both steady-state and random excitations applied at the supports. The study has been simplified by considering a long shear beam, simply supported at two ends; this beam is subjected to two end excitations in the form of ground displacements. Harmonic excitations, differing in phase at the ends, were considered in the frequency domain by analyzing the steady state vibrations and calculating the displacement amplitudes at specific points on the beam. The energy content of the system has been presented, and the correlation between the two end excitations has been considered. For the random excitations, the analysis has been made in the time domain; two different cases of random motions have been considered. The second study develops a method to analyze the dynamic soilbridge interaction of a simple two-dimensional bridge model erected on an elastic half-space, with the input motion in the form of incident plane SH-waves. The bridge model consists of an elastic shear girder supported by two rigid abutments and rigid foundations which have a circular cross section and which are welded to the half-space. Finally, the dynamic response of the bridge and the effect of the radiative damping in the half-space on the interaction of the bridge are also studied.