Performance-Based Assessment of the Effects of Soil-Structure Interaction on the Seismic Demands of Bridge Piers: a Proposed Methodology

Abstract eng:
A methodology is proposed for simplified estimation of the effects of nonlinear soil-structure interaction (SSI) on the ductility and total displacement demands of bridge piers subjected to earthquake ground motions. The methodology is based on modifying the fixed-base demands by applying SSI Modification Factors that are proposed as functions of the ratio of the flexible-base period to the fixed-base period of the piers (Tsys/T). The proposed modification factors are estimated by using response databases obtained from nonlinear dynamic analyses of prototype SSI systems with various combinations of soil, foundation, and structure properties and input ground motions. The response data is processed probabilistically to account for the uncertainties involved in the system properties, such as the natural period, and the scatter of the results of the nonlinear dynamic analyses. The results are presented for various performance objectives and reliability levels. Thus, the SSI Modification Factors can be selected with various levels of reliability chosen by the engineer. The methodology is explained through an application example where SSI Modification Factors are presented by using response databases from nonlinear dynamic analyses of prototype pile-supported bridge piers with various natural periods of the fixed-base structure and soil layer subjected to an ensemble of ground motions. The application of the proposed methodology is shown to be suitable for implementation in a design code. Finally, the paper discusses merits and limitations of the methodology and the need for further research. KEYWORD:

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