Selection of Appropriate Input Motion for Foundation Design in Seismic Areas

Abstract eng:
Engineers often need to use site-specific earthquake ground motions for designing foundations. Seismic design of foundation requires non-linear time history analysis for evaluating soil structure interaction effects. This requires the selection of appropriate time history as input. For the cases where earthquake recorded data is available, manipulation of these records can provide the required site–specific motion to the satisfaction of the all stake holders. However, where these records are unavailable, artificial ground motions need to be generated for analysis and design purposes. Several methods are used in practice for the generation of these artificial ground motions. These approaches include: (a) Direct use of strong motion recorded elsewhere having similar expected earthquake magnitude at the site under consideration; (b) Scaling of strong motion records to the expected P.B.R.A (Peak Bed Rock Acceleration) expected at the location; (c) Code-specified spectrum–compatible ground motion. This paper presents a comparative study on the performance of these three approaches for a typical site where response spectra and the expected peak bed rock acceleration are given. The results indicate that the use of spectrum–compatible ground motion provides least variations in the response parameters. It will be concluded that this third approach provides uniformity amongst the designers and would avoid unnecessary litigations.

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