Experimental Research on Low-Yield-Point Steel Shear Dampers

A new shear metal damper with square tubes serving as out-of-plane stiffeners is proposed. The damper is mainly composed of a core plate, square tubes welded to the core plate, flange plates at two sides and connectors for installation. In this displacement-based metallic device, the input seismic energy is mainly dissipated through the shear deformation of the core plates. The core plates are made of a low-yield-point steel with a nominal yield stress of 225 MPa, called LYP225 steel. This material possesses relatively low yield strength, moderate hardening level and good ductility, hence is suitable for metal dampers.
The paper presents the results of quasi-static tests conducted for evaluating the cyclic elastoplastic response, ultra-low fatigue failure modes and energy dissipation behavior of shear dampers made of LYP225 steel. A total of three full-scale steel shear dampers were tested with the loading condition and flange shape as test variables. The essential mechanical characteristics and ultra-low fatigue behavior of the damper specimens under cyclic loadings were investigated, and the influence of the flange shape to the failure mode was analyzed.
The test results show that the shear damper made of LYP225 steel possesses good ductility (the ultimate shear angle of the specimens achieved 4. 7%), plump hysteretic response (no sign of buckling of components and no pinching of the hysteretic loops observed during the cyclic tests), favorable energy dissipation capacity (the equivalent damping ratio of the specimens stably maintained approximately 0. 5), and satisfying ultra-low cycle fatigue performance (the loads of the specimens under thirty cycles of design amplitude were stable with slight cracks developed). The cracks of the flanges developed at the welding regions limit the deformation capacity and energy dissipation capacity of the dampers. The " dog-bone" configuration for flanges can well delay the initiation of these undesirable cracks and improve the seismic performance of the dampers. The maximum overstrength factor of specimens reached as large as 1. 63, and this hardening phenomenon is beneficial for energy dissipation but need careful consideration for preventing the second damage to the main structural components.