Abstract: “The response of a multi supported structure subjected to spatially varying ground motion at its different supports is of great importance for structures like bridges, pipe lines, viaducts, tunnels etc,. Various reasons like local site conditions, wave passage effect, incoherence effect and attenuation effect tend to induce a phase difference and time lag in the ground motion which results in differential ground motions ateach supports. Assuming that the differential input is available at the various supports the response of the structure can be obtained by the Pseudo-static methods. In these methods the static component of the response is expressed as a function of influence matrix and the input motion which remains independent of the dynamic response. The dynamic component is then computed by using various methods which are then combined with the static components to get the total response. In literature many authors have tried using the modal superposition method for finding the dyna”

Keywords: Multi-support excitation, spatially varying ground motions, bridge, modal vectors, Ritz vectors