Investigation of the Effect of Soil-Foundation-Structure Interaction, Soil Type and Connections on the Behavior of Steel Moment Frames

Structural analysis has significant importance against dynamic and earthquake forces. The responses of structure, foundation and soil to a specified ground motion can be only evaluated using soil-structure interaction. In this study, the effect of modeling beam-column connections, the type of structural systems, the structure height, the type of soil and shallow foundation, and variation of safety factor are studied to assess the seismic responses of steel buildings. For this purpose, five and ten stories buildings with special and intermediate steel moment frames and two different soil types (II and IV) have been considered. Prequalified connections used for these buildings. The footing and strip shallow foundations have been designed for five stories buildings with safety factors of 2, 3 and 4 and strip shallow foundations have been designed for 10 stories buildings with safety factor of 3. Direct method has been selected for the investigation of soil-foundation-structure effects and the nonlinear behavior of soil is modeled using nonlinear Winkler springs. Several 2D finite element models are developed using OpenSees software considering connections, soil-foundation-structure interaction (SFSI) and also without considering these parameters. The modal, nonlinear static pushover and nonlinear dynamic time history analyses are performed for all models. Seven far–fault ground motions are used at this study. Generally, connections and soil-foundation-structure interactions and existing soil type IV have a great influence on structural ductility and responses of steel moment frames, and the lack of them lead to unrealistic consequences. The numerical results are shown that at the models with beam-column connections, SFSI and soil type IV, the maximum lateral displacement and maximum inter-story drift are more than models without connections and fixed based conditions. The maximum base shear of structures at mentioned models are also decreased. At models located on soil type II, maximum values of these three parameters are diminished. At five stories models that situated on soil type IV and included beam-column connections, footing foundations have lower yield resistance and maximum base shear, than models with strip foundations or with fixed based conditions. It is also observed that the structural ductility, maximum base shear are increased with enhancing the safety factor at models with footing foundations, but changing safety factor at models with strip foundations leads to very small difference at above parameters. The safety factor and foundation types have not any effect on yield resistance and seismic responses of structures that located on soil type II. Keywords: Soil-foundation-structure interaction, beam-column connections, nonlinear Winkler springs, soil type II and IV, shallow foundation, safety factor.