Performance-Based Design of Geotechnical Structures: Recent Advances

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• Professor Susumu Iai, Disaster Prevention Research Institute, Kyoto University
• Friday 05 March 2010, 16:30-17:30
• Engineering Department - LR6.

If you have a question about this talk, please contact Zelda Stuck.

An overview is presented on the recent advances in earthquake geotechnical engineering with respect to the seismic design of geotechnical structures. In conventional seismic design, many factors that should be considered for design are specified rather than evaluated. The principles in performance-based design presented in this lecture are much more generalized and allow the experienced practicing engineers and code writers go back to the critical issues in design, including performance criteria to specify the design parameters. The modern principles in seismic design presented in this lecture allow a sophisticated approach to deal with the uncertainty. The life-cycle cost approach is an promising approach. The optimum design in the life-cycle cost approach has a certain probability of failure. This probability is not prescribed by an authority (such as 10% over 50 years) but rather determined as a result of the minimum life-cycle cost procedure.

Strong non-linearity in site-response recorded through instruments during earthquakes is different from the view based on the equivalent linear or non-linear models without the effect of dilatancy. The non-linearity does not diminish the high frequency nature of the accelerograms, or necessarily reduce the peak acceleration that can exceed 1g as manifested by the strong motion record during the 2004 Niigataken-chuetsu and the 2008 Iwate-Miyagi inland earthquakes.

Strong non-linearity in soil-pile interaction is identified as the manifestation of strain localization in the vicinity of the pile side. Load-displacement curves of a pile for saturated sand deposit follow a hardening-spring type shape similar to the stress strain curve during cyclic mobility of saturated sands. The effects of soil-pile separation are significant in the behavior of a single and group piles. These facts direct us to a critical view on the conventional design recommendations for designing pile foundations.

Facing with the highly non-linear response of soil-structure systems during strong earthquake motions recorded in recent years, we may well be going back to the basics of understanding the mechanism of soil-structure interaction as is rather than hastily jumping into adopting a simplified method and trying to temper the model parameters in order to get the simplified model fit the recorded case histories.

Combined hazards, such as those at the 2004 Sumatra earthquake, poses a new challenge to the geotechnical earthquake engineers. The use of design charts, that reflect a series of comprehensive parametric studies based on the effective stress analysis, may be one of the efficient approach to meet this challenge.

This talk is part of the Engineering Department Geotechnical Research Seminars series.

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