Evaluation of Load Patterns in Nonlinear Static Analysis for Estimating Dynamic Behavior of Structures Including Soil-Structure Interaction

In the last ten years, nonlinear static analysis, commonly denoted as pushover analysis, has become the forefront for determining the ultimate load and the deflection capability of a structure. Therfore, an important step in performance base design is to estimate the nonlinear seismic response of buildings. In pushover analysis the magnitude of the structural loading is incrementally increased until a predetermined target displacement is reached at a monitoring point. Nevertheless, the method is limited by the assumption that the response of the structure is controlled by its fundamental mode. Moreover, in the seismic analysis of structures, it is often customary to idealize the buildings as fixed at base. The influence of soil-structure interaction (SSI) implies restrictive applicability of dual-design system since the total displacement of system includes the elastic and inelastic displacements of the structure plus displacement resulted from foundation movement. Therefore, the evaluation of SSI effects on nonlinear structural responses is the objective in this study. Insight into SSI phenomenon has been achieved through the pioneering studies. However, most of these studies have generally been directed by the exclusion of non-linear behavior of structures. The current paper evaluates a new pushover procedures which can take into account higher mode effects considering soil-structure interaction. The procedure utilizes single-stage and multi-stage pushover analysis and the concept of cone models is employed to evaluate the effects of soil-structure inertial interaction on dynamic response of structures. The structural responses are determined by enveloping the results of single-stage and multi-stage pushover analysis. In addition, a comparison between the new procedure and the exact values obtained from nonlinear dynamic analysis, as well as modal pushover analysis (MPA) has been carried out. The new pushover procedure is more accurate than the FEMA load distribution as well as MPA procedure in predicting seismic demands of structures

Keywords:

Pushover-based Nonlinear Static Procedures , Nonlinear Seismic Demands , Soil Structure Interaction , Higher Mode Effects