Effects of Height and Number of Bays on the Seismic Behavior Factor of R.C. Moment-Resisting Frame Structures Including Soil-Structure Interaction

Abstract In this study, the impacts of structure height and number of bays on the seismic behavior factor R of reinforced concrete (RC) moment-resistant frames are investigated with the consideration of soil-structure interaction (SSI) effects. For this purpose, 2-, 5-, 8- and 11-storey RC moment-resisting frame structures with the variation of the number of bays for each structure height are selected and designed according to the Algerian seismic code RPA 99/Version 2003. Three different soil deposit classes suggested by ATC 40and FEMA 356 are taken as reference to choose the mechanical properties of the soil. Fixed-base models and soil-structure interaction models using the substructure approach are analyzed by performing non-linear static pushover analyses in order to compute the R factor components, such as ductility and overstrength factors, with the consideration of failure criteria at both member and structural levels. Furthermore, to highlight the effect that could have the mechanical response of the soil on the R factor, two different soil responses are adopted, namely, elastic linear and elastoplastic nonlinear consecutive models. The results show that, for fixed-based models, the value of the seismic behavior factor decreases as the structure height increases, whereas for the number of bays parameter, the R factor seems to not be influenced at all. For the flexible base models, the tendency observed is the same as in fixed-base models, but with substantially lower values of R, particularly in soft soil with an elastoplastic nonlinear consecutive model. This implies that SSI has detrimental effects for RC frame structures under seismic action. These observations are extremely significant for most seismic design codes, which at present do not prescribe any link between the seismic behavior factor intended to represent structural ductility and the SSI.