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Self-Centering System To Protect Buildings During an Earthquake

Self-Centering System To Protect Buildings During an Earthquake

Structural systems that bring a building back to upright position after an earthquake (“self-centering” systems) have existed for some time, but they are not commonly used because they involve unconventional construction methods and costly materials. BYU Honors student Emma Kratz-Bailey and her faculty mentor Johnn Judd are developing a self-centering system for steel-frame buildings that aims to address these issues by employing commonly applied construction methods and materials. In the proposed system, shear is transferred through a standard slotted shear tab beam connection, and flexure is transferred through buckling restrained steel struts that are embedded in the floor above the beam and a seat angle below the beam. Post-tensioned strands act in concert with the steel struts within the concrete or wood floor to re-center the building. In the first phase of the study, two full-scale prototypes of the proposed building system were constructed and tested in the structures lab using a quasi-static fully-reversed cyclic loading protocol to mimics earthquake shaking. The tests of the concrete floor building showed that the proposed system was able to achieve the required story drift for moderately ductile steel moment frame buildings and it was able to isolate the beam from column rotation up to 3% story drift. After 4% story drift, the gap between the floor and the column was insufficient to prevent the strut tabs from ramming into the floor. A wood floor building system with a larger gap was tested. The system showed improved ability to re-center the building and had smaller flexural strength compared to the concrete floor building. The results suggest that the proposed concept is viable, but several details of the system (such as the gap between the column and the floor, the strength of the concrete floor, and the thickness of the bearing plates for the struts) need to be refined in the next phase of the study