Keywords: seismic evaluation, soil-structure interaction, hysteretic energy, inelastic inter-story drift ratio, optimisation.

This paper deals with the evaluation of the seismic behavior of reinforced concrete moment resistant frames (RC-MRFs) considering soil-structure interaction (SSI) effects. The parameters that are usually used for seismic performance evaluation of structures are the inelastic inter-storey drift ratio and plastic hinge rotation at the each end section of the structural elements. In addition to the mentioned parameters, the parameters based on energy concepts including input and hysteretic energy dissipation (HED) of structures during an earthquake excitation can be used for this purpose [1].

On the other hand, during an earthquake, SSI effects play an important role in determining the behaviour of structures constructed on the relatively soft soil. Hence, SSI effects between soil and structure should be considered in the seismic behaviour of structures [2].

In this paper, a direct method is employed for the modeling of the SSI system. In this method, discretized dynamic equations of the structure and soil are considered simultaneously. The infinite boundaries of the soil under the structure are modelled using viscous boundaries. The finite element model of the SSI system is established using OpenSees, a structural analysis software framework for nonlinear analyses. The soil is layered with constant material properties along its depth, and the foundation is considered as a rigid strip footing.

To evaluate the seismic energy demand of RC-MRFs, a nine-storey three-bay RC-MRF optimally designed based on the recommendations of the design codes is considered. In this regard, the frame is designed using an optimisation technique and the minimum structural cost is considered as an objective function. The discrete particle swarm optimisation (DPSO) algorithm [3] is utilized to perform the optimisation process. Six strong ground motion records are selected for the evaluation of the seismic energy demand of the frame. Consequently, the inelastic inter-storey drift ratio and HED of the frame for each record are investigated with and without considering the SSI effects. The results show that as a result of considering the SSI effects on the structure, the non-linear responses tolerate numerous variations.

1

C.M. Uang, V.V. Bertero, "Evaluation of Seismic Energy in Structures", Earthquake Engineering and Structural Dynamics, 19(1), 77-90, 1990. doi:10.1002/eqe.4290190108

2

J.P. Wolf, S. Chongmin, "Some cornerstones of dynamic soil-structure interaction", Engineering Structure, 24, 13-28, 2002. doi:10.1016/S0141-0296(01)00082-7

3

E. Salajegheh, S. Gholizadeh, M. Khatibinia, "Optimal Design of Structures for Earthquake Loads by a Hybrid RBF-BPSO Method", Journal of Earthquake Engineering and Engineering Vibration, 7(1), 14-24, 2008. doi:10.1007/s11803-008-0778-y

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