DEFORMATION CAPACITY OF HYSTERESIS DAMPERS USING BENT STEEL PLATES FOR BASE-ISOLATED STRUCTURES

Abstract

 In this study, a hysteresis damper using bent steel plates for base-isolated structures (BSPD) is proposed. The BSPD comprise four steel plates bent into a trapezoid. The bent steel plates are connected together in the shape of a cross to reduce the influence of the loading direction on mechanical behavior. In chapter 2 and 3, the cyclic shear loading tests are conducted to investigate the influence of the shape of the bent steel plates on mechanical behavior of the BSPD. The conclusions of this chapter are as follows.

 1. The loading direction has little influence on the load-deformation relationship including the yield strength and initial stiffness.

 2. Failure mode are classified according to the load amplitude and direction. In all failure modes, the crack occurs near the bolt holes.

 1) d=100mm, 0°: The bent steel plates parallel to the load are broken.

 2) d=100mm, 45°: The crack propagates perpendicularly to the load.

 3) d=100mm, 0°: The steel plates parallel or perpendicular to the load are broken.

 4) d=200mm, 45°: The steel plates perpendicular to the load are broken.

 3. The yield strength _iQ_y and initial stiffness _iK_ini increase with thickness t. The deformation capacity decreases as t increases. The diagonal plate length h has little influence on _iQ_y and _iK_ini. The deformation capacity increases with h. The diagonal plate height g has little influence on _iQ_y, _iK_ini and the deformation capacity.

 4. The specimen of the steel type SN490B has larger strength as the specimen of the steel type LY225. However, the specimen of the steel type LY225 has larger deformation capacity as the specimen of the steel type SN490B.

 5. The deformation capacity n_t is correlated with the plate spring stiffness _iK, and n_t increases as _iK decreases. Due to the original experimental plan, there are bolt holes in the bent steel plate. However, in the experiment, the crack occurs near the bolt holes, which led to the strength deterioration. Therefore, in chapter 4, finite elements (FE) analysis are conducted to investigate the influence of the bolt holes on deformation capacity. The conclusion of this chapter is as follow.

 6. The FE analysis indicates that the bolt holes make the local strain increase, and to eliminate the bolt holes is effective for improving the deformation capacity.