Preliminary Studies of the Effects of Degrading Infill Walls on the Nonlinear Seismic Response of Steel Frames

Keywords: Seismic Response, Steel Frames, Infill Walls, Nonlinear Static Analysis, Infilled Frames, Capacity Spectrum Method, Computer Codes, PREPF, Preprocessor for Framed Structures, STAND (Computer Software), Static Analysis and Design Program, Dynamic Loading, and Modeling.

Abstract: The effects of infills on the nonlinear response of steel frames was studied. The primary goals of this preliminary investigation were: 1) to incorporate degrading infill wall models into a nonlinear steel frame analysis program, 2) to compare the nonlinear response of a series of frames with and without infills, and 3) to utilize the Capacity Spectrum method to estimate the demand for several earthquake spectra. The equivalent strut model was adopted to represent degrading infill walls which did not have any openings. A nonlinear static analysis program was used to calculate the load-displacement curves of a variety of steel frames. As expected, the walls increased the capacity of the frames and decreased their initial periods. The number of hinges in the frame decreased significantly. Most of the peak lateral displacement was caused by deformations in the first story if the frame had infills at all levels. The analysis performed in this study provided good preliminary estimates of the effects of infills on frame response. Additional experimental data is needed to refine the models and to extend their applicability to walls with openings and to evaluate the effects of walls on local frame member behavior.