Development of seismic infill wall isolator subframe (SIWIS) system

by Aliaari, Mohammad.

The Seismic Infill Wall Isolator Subframe (SIWIS) system is developed in this study for use in building frames with masonry infill walls in order to prevent damage to columns or infill walls and to minimize life-safety hazards during potentially damaging earthquakes. Because of the conventional tight-fit construction within structure frames, 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 because the infill wall is usually treated as a non-load bearing wall, and, thus, is not designed to carry in-plane loads. Complete isolation of infill walls by separation gaps as an alternative construction suffers from lack of convenient and satisfactory solutions for fire and acoustic protection of the gap and the out-of-plane stability of the wall. The SIWIS system, which consists of two vertical and one horizontal sandwiched light-gauge steel studs with SIWIS 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 severe damaging events. The SIWIS system acts as a “sacrificial” component or a “structural fuse” to protect the infill wall and frame from failure. An experimental testing program planned and carried out tested the concept of the SIWIS system. The experimental program mainly included a series of tests on three different designs for fuse element (centerpiece) including concrete disk, steel disk, and lumber disk followed by a series of in-plane static pushover tests on a scaled two-bay three-story steel frame in three forms of bare frame, rigid frame, and pinned frame equipped with an SIWIS device. Generalized nonlinear finite element modeling schemes were developed for infilled steel frames with and without SIWIS system. Validation of modeling schemes was accomplished by comparing the experimental observations with the numerical predictions for: (1) a previously tested and studied single-bay single-story infilled steel frame selected from the literature; and (2) the tested two-bay three-story steel frame. The analytical and experimental results show that the concept of the proposed system works as a “seismic isolation” system for infill walls by utilizing, initially, the beneficial stiffness and strength effects of the infill wall up to a predefined point, but, ultimately isolating the infill wall from the frame for their safety. Practical design approaches were proposed and applied to three examples including: low rise, mid-rise, and high-rise buildings in high seismic and wind zones to demonstrate the performance of the proposed system. iv