Pushover analysis of masonry infilled steel frames with seismic infill wall isolator subframe (SIWIS) system

Because of the conventional tight-fit construction of masonry infill walls within structure frames and their large in-plane stiffness, infill walls participate in resisting wind and seismically induced loads. Although beneficial during wind loads and minor earthquakes, the lateral load resistance of infill walls during strong events can damage the wall or the frame. The Seismic Infill Wall Isolator Subframe (SIWIS) system is developed for use in building frames with masonry infill walls in order to prevent damage to columns or infill walls and minimize life-safety hazards during potentially damaging earthquakes. The SIWIS system, which consists of two vertical and one horizontal sandwiched light-gauge steel plates with "rigid-brittle" elements in the vertical members, is designed to allow infill wall-frame interaction under wind loading and minor to moderate earthquakes for reduced building drift but to disengage the infill wall-frame interaction under damaging events. In this paper, the SIWIS system is briefly introduced and preliminary analysis results for a single-bay, single-story infilled frame system and a two-bay, three-story frame with masonry infill walls, with and without SIWIS elements (in each bay) are presented. Details of the finite element modeling are described and the analysis results, including loaddisplacement relationships and failure modes, are explained.