Study On The Rocking Wall Frame Structure With Buckling-Restrained Braces In Base

Buckling-restrained brace (BRB) is a kind of seismic resistance device with favorable energy dissipation capacity. Nevertheless, due to the low post-yield stiffness of BRBs, frames equipped with BRBs as main lateral resisitance system (BRBF) are prone to be under a weak layer effect, which may lead to a large residual deformation after the earthquake, raise the difficulty of structure repairment and the cost, and this effect will limit the development and application of BRB. Effectively controlling the location and degree of damage of the BRBs can make full use of the energy dissipation ability of BRB and can help obtain the goal of "repairable" or "easy to repair"of the frame structure. Rocking wall, used as a typical component of controling structure deformation mode, have an ability to rotate with large lateral stiffness at the bottom, which can effectively control the structural damage location and damage degree. Based on the structural level, this paper puts forward the conception of a hinged wall with BRBs in base (HWBB) and the frame with HWBB (HWBBF), which can make full use of the BRB energy dissipation ability and be repaired conveniently after strong earthquakes. The HWBB can provide the lateral stiffness, and the attached frame is assumpted to provide the stiffness of gravity only, so the HWBBF is applicable to precast frame with low stiffness. The HWBBF is convinent to be repaired after the strong earthquake and can be produced on a industrialized scale. The research contents and results of this paper are as follows:(1) In this paper, the structure system and seismic resistance of HWBBF were presented. The seismic performance of HWBBF was conducted by the nonlinear time history analyses. The modal analyses were addressed through the simplified modal of HWBBF, and the results indicate that the variation of rotational stiffness ratio has a large effect on the first-order period, while little effect on high-order periods. A project designed as HWBBF was analysed and the nonlinear time-history analyses were conducted, which indicated that performance objectives could be satisfied and the deformation mode was dominated by the first modal shape. The base shear and the central moment showed a considerable increment after the appearance of plastic hinge at the bottom of HWBBs. A simplified design method, which means the superposition of intensity of ground motion, was presented for estimating the internal force of wall. The estimated values of equations were compared with the results of time-history analyses, which proved the good precision of this method.(2) A series of experiments under El Centeo seismic wave were conducted on a 1:3 scaled HWBB specimen, including pseudo-dynamic, pseudo-static and repairment experiments. The experimental results indicated that rocking wall remained elastic while BRBs dissipated seismic energy during the experiment, and the damage mechanism of the HWBB was in accordance with preconceived. The repairment process of resudial displacement after earthquake which applied moment to the specimen was convenient and controllable. The global hysteretic curves of structure under pseudo-static load were stable and HWBB behaved in a ductile and stable manner without strength degradation even when the test structure was pushed to a drift of 2.5%. One of the BRBs in H WBB ruptured at the end, which indicated a controllable characteristic of failure mode. After replacing BRBs, pseudo-dynamic and pseudo-static experiments were conducted again and the global hysteretic curves wrere nearly identical before and after replacement of BRB.(3) A series of finite element analyses were conducted on the specimen by SAP2000 to assess the effectiveness of different repairment methods. The pseudo-dynamic loading process and repairment after earthquake were modeled and the results indicated that the modeling results conincide with experimental results well, considering the sliding of pin at the bottom of wall and the tilting of ground beam, while BRB of trilinear model could reflect its actual hysteretic response precisely. On this basis, the effect of applying counter torque on one side or both sides were compared, indicating that applying counter torque on both sides cause less internal forces. The effects of loading precise or estimated displacement showed that displacement-controlled repairment has less requirment for accuracy of the model and repair effect coluld be ensured by loading estimated displacement.