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Simplified approach for design of raft foundations against
fault rupture. Part II: soil-structure interaction

I. Anastasopoulos1,2, N. Gerolymos1, G. Gazetas1 and M. F. Bransby2

1. School of Civil Engineering, National Technical University of Athens, Greece
2. Civil Engineering, University of Dundee, Scotland, UK

Abstract: This is the second paper of two, which describe the results of an integrated research effort to develop a four–step simplified approach for design of raft foundations against dip-slip (normal and thrust) fault rupture. The first two steps dealing with fault rupture propagation in the free-field were presented in the companion paper. This paper develops an approximate analytical method to analyze soil–foundation–structure interaction (SFSI), involving two additional phenomena: (i) fault rupture diversion (Step 3); and (ii) modification of the vertical displacement profile (Step 4). For the first phenomenon (Step 3), an approximate energy–based approach is developed to estimate the diversion of a fault rupture due to presence of a raft foundation. The normalized critical load for complete diversion is shown to be a function of soil strength, coefficient of earth pressure at rest, bedrock depth, and the horizontal position of the foundation relative to the outcropping fault rupture. For the second phenomenon (Step 4), a heuristic approach is proposed, which “scans” through possible equilibrium positions to detect the one that best satisfies force and moment equilibrium. Thus, we account for the strong geometric nonlinearities that govern this interaction, such as uplifting and second order (P−Δ) effects. Comparisons with centrifuge–validated finite element analyses demonstrate the efficacy of the method. Its simplicity makes possible its utilization for preliminary design.

Keywords: fault rupture; semi-analytical expression; soil-structure interaction; earthquake

 

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Copyright© 2009 IEM. Journal of Earthquake Engineering and Engineering Vibration. All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as described below, without written permission from the Publisher. Copying of articles is not permitted except for personal and internal use, to the extent permitted by national copyright law, or under the terms of a license issued by the National Reproduction Rights Organization of China.