Analysis of masonry infilled steel frames with seismic isolator subframes

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 studs 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 them under damaging events. The SIWIS system acts as a “sacrificial” element just like a “fuse” to save the infill wall and frame from failure. Nonlinear finite element models for two cases, a single-bay, single-story steel frame and a two-bay, three-story steel frame, in three forms including bare frame and infilled frame with and without SIWIS system were performed to develop an understanding of how the system responds to lateral loading. Analysis results show that the concept of SIWIS system works in providing initially high stiffness followed by an isolation of infill wall from interaction with the confining frame. Practical design guidelines are proposed and applied to an eight-story office building.