Research On Seismic Performance Of The Rocking Wall Frame Structure With Buckling-Restrained Braces

At present, design methods of buckling-restrained braced frames (BRBFs) are usually complex processes with lots of parameters. In particular, it is difficulty to make sure buckling-restrained braces (BRBs) in all floors yield simultaneously and avoid the weak story. While in rocking wall frames, rocking walls provide no additional lateral resistance and energy dissipation capacity. Based on the design complexity of BRBFs as well as the stiffness and energy dissipation demand of rocking wall frames, a kind of rocking wall frame structure with BRBs is proposed. On the one hand, it can be considered that the deformation pattern of the BRBF is well controlled by rocking walls to make full use of BRBs. The other hand, it can be regarded as a rocking wall frame in which BRBs provide lateral stiffness and consume seismic energy. The main work and conclusions are as follows:(1) The dynamic characteristics of rocking components, which are regarded as independent and elastic, and mechanical characteristics of rocking wall frames are analyzed. The time history analysis method and several mode solving methods of rocking components are discussed. The restoring force modal is explored by the mode-superposition method. The results of forced resonance analysis show that internal forces are mainly affected by higher modes, while displacements are controlled by the first mode. Through the mechanical analysis of the rocking wall frame, the main design parameters such as the stiffness ratio are presented. When the lateral stiffness and height of the frame are uniformly distributed, the addition of rocking walls has no influence on the ratio of the base shear and the roof displacement, otherwise the ratio will be affected. Rocking walls play the role to transfer lateral stiffness, thereby improving the lateral resistance of the whole structure.(2) The rocking wall frame structure with BRBs is proposed. The design concepts and advantages of this structure are described firstly. Through the mechanical analysis of the structure, the main design parameters such as the rotational stiffness ratio are presented. Compared with rocking components, the results of forced resonance analysis of hinged wall with BRBs in base (HWBB) show that, with the increase of the rotational stiffness ratio, the effect of the first mode on internal forces and that of higher modes on displacements both raise. Based on the Benchmark model, the seismic performance comparisons between this structure and others are conducted. The results confirm that:before BRBs yield, this structure performs similarly to the shear wall frame, in which additional lateral stiffness is provided by BRBs and transferred by rocking walls; after BRBs yield, the structure tends to rock, in which rocking walls control the lateral mode and BRBs consume seismic energy, leading to full use of the seismic capacity of each part.(3) Three kinds of stiffness ratio (named as the stiffness ratio, the rotational stiffness ratio and the post-yield stiffness ratio) in the hinged wall with BRBs in base frame (HWBBF) are investigated by means of dynamic analysis, and the results are as follows. Whether in the rocking wall frame or the HWBBF, when the stiffness ratio is large enough, the lateral mode of the structure is more approximate to that of walls, which means a good control effect. For the HWBBF whose stiffness ratio is great, with the increase of the rotational stiffness ratio, the lateral mode gradually transforms from the rocking wall-pattern to the shear wall-pattern. Moreover, the base shear and the central moment increase while the roof displacement and the peak inter-story displacement angle show little change. Without consideration of the P-A effect, no matter what value the post-yield stiffness ratio is, the HWBBF is basically in agreement with the equal seismic displacement principle. However, with consideration of the P-A effect, the smaller the post-yield stiffness ratio is, the greater the roof displacement and the residual displacement will be. Nevertheless, when the post-yield stiffness ratio is larger than 0.1, the structural responses are almost free from the P-A effect.(4) Analysis on the design method of the HWBBF is conducted. The conversion relationships of the basic seismic capacity elements (bearing capacity, lateral stiffness, lateral displacement and ductility) between BRBs and the HWBBF are derived according to the geometric relationships. Among them, the ductility relationship is analyzed and the results indicate that the ductility of the structure is not only related with that of BRBs, but also affected by the rotational stiffness ratio. After BRBs in base yield, the base moment of the HWBB will not increase, yet the central moment can still generate significant increment. According to the distribution of post-yielding moments of the HWBB, a superposition method is proposed and verified. The results show that the method is convenient and accurate.