A Simplified Non-Linear Spring Approach for Dynamic Soil-Structure Interaction

Abstract eng:
The linear behavior of the soil is only valid for very small level of strain. Therefore, the deformations induced by a seismic motion in the soil can easily reach the limit of its linear elastic domain. Consequently, it is very important to develop methods for taking into account the non-linearity of the soil in the problem of the dynamic soil-structure interaction, especially for moderate to strong motions able to induce damage on the superstructure. With the aim of making a simplified dynamic soil-structure interaction analysis, instead of a complete costly numerical modelling which includes the soil and the superstructure, it is possible to model the soil by springs which have equivalent characteristics (Winkler’s springs approach). Thus, in order to take into account the non linear behavior of the soil, the use of springs with bilinear elastoplastic behavior is investigated. For each simplified model, two sets of springs are used: one for vertical displacements and the other for the horizontal one. The investigated structure is a two-story reinforced concrete frame placed on a rigid shallow foundation. Plastic-hinge beam-column elements are used to represent the behavior of reinforced concrete structural elements. The values of the springs’ parameters are obtained by matching the dynamic non-linear structural response of the proposed simplified approach and a complete 2D finite element analysis using a realistic constitutive model for the soil. In order to obtain the optimal set of springs’ parameters for a given input motion, an optimization procedure based on the value of the induced structural damage is applied. It is shown that for a given optimal set of springs’ parameters, the accuracy of the simplified method is strongly correlated with the frequency content of the input. Thus, an applicability domain can be established for a set of parameters in terms of the soil classification and frequency contents of the motion.

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