MULTIPLE-SUPPORT SEISMIC ANALYSIS OF LARGE STRUCTURES

The effect of the spatial variation of earthquake ground motion on the dynamic response of multiple-support structures may be important. The relative performance of two simple analytical methods to model multiple-support seismic analysis of large structures is investigated. These are the relative motion method (RMM), which divides the structural response into a dynamic response component and a pseudo-static response component, and the large mass method (LMM), which attributes fictitious large mass values at each driven nodal degree of freedom (DOF) to obtain the total response of the structure. The seismic response of a four-span bridge using the traveling wave assumption is used to illustrate the practical application of the methods. It is found that the LMM is able to yield results that are almost identical to those of the RMM using large mass values equal to approximately 107 times the total mass of the bridge. Parametric analyses where the travel wave speed is systematically varied show that the structural response tends to increase as the wave velocity decreases and can become significantly larger than the response obtained from synchronous excitation. © 1990.