Influence of Ground Motion Incoherency on Earthquake Response of Multi-Support Structures

Report No. CCEER 02-2This report focuses on analyzing the influence of three factors: geometric incoherency effect, wave-passage effect, and local site effect on the seismic response of multi-support linear structures using response history analysis. The computer programs were developed in Northern Jiaotong University. A one-span frame and a reduced model of a 24-span bridge, located in Las Vegas, Nevada were studied, in which the influence of each of the three factors, and their combinations was analyzed. The analytical model was linear and was used to determine the longitudinal response of the structures. It was revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamic response of uniform base excitation and inducing pseudo-static response which does not exist in structures subjected to uniform ground motion. The structural response when ground motion incoherency is considered may be larger or smaller than that of uniform excitation, depending on the position, the response, soil conditions, and ground motion. When all three sources of incoherency were included in the analysis, analyses showed that the internal forces could be substantially larger than those of uniform motion