M Abbasi - Shiraz University of Technology
E Hosseinkhani - Shiraz University of Technology
H Rahnema - Shiraz University of Technology
S.M Binesh

In the traditional dynamic structural analyses, free field responses of the site being used as the foundation input motion. To consider the effects of earthquake torsional motion, an accidental eccentricity is assumed at the imposition point of earthquake forces. However, studies on kinematic soil-structure interaction show that assuming a fixed value for eccentricity by ignoring the geometry and mechanical characteristics such as foundation dimension, soil shear wave velocity, angle of incident wave and the natural frequency of structure significantly reduces the accuracy of results. In this paper an efficient approximation formula is implemented for the estimation of foundation input motion. The lateral and torsional acceleration response spectrum of Iranian earthquakes are evaluated and, changes in the response spectrum with respect to the changes in the ratio of the foundation dimension to the shear wave velocity is also investigated. At the end of the paper the obtained lateral and torsional response spectral for each type of soil are used to estimate the required accidental eccentricities for common structural analysis.

Torsional Motion, Kinematic Soil-Structure Interaction, Accidental Eccentricity