Seismic fragility assessment of steel frame structures equipped with steel slit shear walls

Abstract

The steel slit shear wall (SSSW) dissipates seismic energy through the developed plasticity at steel plate links separated by cutting slits. Its shear hysteretic behavior is influenced by parameters such as link configuration, amplitude of out-of-plane deformation and steel property. To investigate the contributing factors for different types of shear hysteretic behavior, four SSSW specimens with design parameters of link configuration (flat or twisted) and steel property (common carbon steel or low yield steel with significant strain hardening) are designed and tested under quasi-static cyclic loading. Four types of shear hysteretic behaviors are obtained: pinched, pinched without cyclic degradation, plump and combined (plump first and pinched later). Though pinching also occurs in the SSSW with twisted links, there is no strength and stiffness degradation in the hysteresis. Thanks to the strain hardening of low yield steel, the low yield SSSW presents plump hysteresis. These different shear hysteretic behaviors are successfully simulated using macro models firstly, including user-defined models for the pinched type without cyclic degradation and the combined type. Then moment resisting steel frame (MRSF) models equipped with these SSSWs are built respectively to study their influence on the overall structural performance. Results of fragility analysis show that four types of SSSWs enhance the seismic performance of MRSF structures at both small and moderate damage states nearly in the same degree. At extensive and collapse damage states, the SSSW with twisted links performs the best, followed by the low yield SSSW.