Generation of Non-uniform support accelerations of topographic site using one recorded accelerogram

Abstract

This study investigates method of producing non-uniform support acceleration in actual site condition. Factors affecting the non-uniform excitation of topographic site include time delay between the arrival time of incident wave at the canyon floor and any particular point at higher elevation, causing phase difference. Another important factor in generating non-uniform accelerations is the topography amplification. Therefore, in the present study, two dimensional models of a canyon site subjected to Ricker wave with different predominant frequencies, shear wave velocities, shape ratios have been developed and the results of boundary element analyses in time domain (HYBRID code) were obtained in different elevations on the canyon surface. Then, by conducting a series of statistical analyses (Symbolic Regression and Genetic Programming) on the results from numerous presumed cases, the relationships for calculating the time delay between support responses of V-shaped canyons was obtained. To verify the accuracy of the proposed relationships, the results were compared with the records from Pacoima dam site during two different earthquakes and good agreement of the results was observed. Eventually, by implementing the presented relationships into random vibration method, non-uniform acceleration of the site was simulated. The results indicate that the proposed relationships have an appropriate level of accuracy to calculate time delay on the V-shaped canyons.

Keywords

• non-uniform excitation
• site effect
• time delay
• amplification
• boundary element