DYNAMIC SOIL-STRUCTURE INTERACTION OF DUCTILE STEEL FRAMES IN SOFT SOILS

Results of static and dynamic nonlinear analysis of ductile steel frames of 8- and 12-stories buildings are discussed in this paper. The influence of dynamic soil-structure interaction in deformation demands, failure mechanism, ductility and overstrength capacities and maximum demands in columns were analyzed. For this purpose, buildings were designed and studied under three boundary conditions: (i) fixed-base (no Soil-Structure Interaction), (ii) pile foundation and (iii) mat foundation condition. The influence of the lateral stiffness was studied through the response of moment resisting frames (unbraced frames), 1-braced bay frames and 2-braced bays frames. Soil foundation dynamic stiffness (impedance function) is introduced by a set of springs in horizontal and rocking direction, which were computed from the dynamic behavior and properties of the soil-foundation system. It was found that fixed base model might not be a conservative representation of the response of buildings with flexible foundations, especially when a pile foundation system is considered.