Baikuntha Silwal, Osman E. Ozbulut 2018
The performance of steel buildings designed with superelastic viscous dampers (SVD) was assessed under mainshock and aftershock seismic loading sequences. A case study that consisted of a nine-story steel structure was tested with a special moment resisting frame (SMRF) and a reduced strength SMRF equipped with SVDs. Incremental dynamic analysis (IDA) are performed on the steel structures to simulate mainshock and aftershock loading conditions. The continued ability of the mainshock-damaged steel structure, equipped with SVDs, to withstand aftershocks was evaluated. The aftershock fragility assessment and collapse capacity at demolition are analyzed in the steel building systems to improve seismic performance and mitigate residual drifts of steel frame building.
System Concept
Shape memory alloy (SMA), which displays favorable re-centering and energy dissipation capacity, is investigated in their effectiveness to be strategically utilized to develop superelastic viscous damper (SVD). The SVD efficiently combines SMA cables and a viscoelastic damper. The SMA cable provides high tensile force capacity, while the damper uses butyl rubber compounds bonded to steel plates that significantly dissipate energy and reduce residual drift.
Experimental Study, Results and Discussion
The aftershock performance of a steel building with SMRF was investigated and compared to the performance of the building with the SVD. The superelastic viscous dampers are tested in a steel MRF, which consists of five bays spanning along each direction in addition to a basement. Alternatively, the structural system that consisted of SMRF on the perimeter of the building resisted lateral forces. A FE model simulated the SMRF in different loading conditions to evaluate degradation in structural strength and stiffness of the steel frame. Three damage states were identified through a mainshock incremental dynamic analysis for the SMRF and SVD frames. An aftershock incremental dynamic analysis was performed and results displayed that the collapse capacity of the mainshock-damages SVD frames did not significantly decrease with increasing mainshock damage. Not only did the SVD frames show a higher median collapse capacity than SMRF after the mainshock, but a continued higher collapse capacity after aftershocks. The aftershock performance of the SVD in steel structures was not affected by the intensity of the mainshock. The SVD frame was successful in improving seismic performance, especially improving aftershock capacity, reducing residual story drifts.
Reference
WBaikuntha Silwal, and O. E. Ozbulut.; (2018). “Aftershock fragility assessment of steel moment frames with self-centering dampers.” Engineering Structures