| The application of buckling restrained brace (BRB) is an effective means to reduce the structural damage which has a good energy dissipation capacity. However, due to the low post yield stiffness, the BRB frame under the strong earthquake is prone to endure large residual deformation, which made an increasing of the difficulty and the cost to the restoration of the structure after the earthquake. In order to solve the problem, self-centering (SC) system is led into the BRB and formed the self-centering buckling restrained brace with pre-tensioned tendons (SC-BRB), which has a good energy dissipation capacity and self-centered ability simultaneously. Compared to the BRB, SC-BRB has a hysteretic curve with the obvious characteristics of features of the shape flag due to the introduction of the self-centered system, with more parameters of the hysteretic performance and more complex influencing mechanism of seismic performance to the braced frame structure. However, the study of the parametric study about the seismic performance of SC-BRB frame at present is still relatively scarce, and the research for seismic design method to SC-BRB framework is also short, which has limited the popularization and application to the SC-BRB. In this paper, the author has made a further research on the influence regularity of the key design parameters on the seismic behavior of frame of SC-BRB, which is mainly focused on the hinged frame and dual system, considering different number of layers. On this basis, the author established the design method and process of the SC-BRB framework based on direct displacement, and the main contents are as follows:(1) The construction, the working mechanism and the relationship between key construction parameters and hysteretic parameters of SC-BRB are analyzed in detail. The refined finite element model for hysteretic analysis of SC-BRB is established in OpenSees. Based on the OpenSees model and quasi-static test results of components, the influence of the tube length tolerance on the initial stiffness of self-centering system is studied. The range for the initial stiffness of self-centering system is determined, which establishes the foundation for the finite element modeling and parameter analysis of SC-BRB frame.(2) Prestressed tendons of SC-BRB may fracture under strong ground motion. For this problem, the setup and numerical simulation of braces with friction device at end are studied. And the simplified finite element model of SC-BRB for structural seismic performance analysis is also established. According to the ASCE7-10 code, three braced frames with pinned connections (4-story,8-story and 12-story) and three dual system are designed. The influence of initial stiffness’ change in self-centering system on structural seismic performance is studied through pushover analysis and nonlinear time history analysis. The results show that the minimum initial stiffness considering the tube length tolerance is conservative in the process of SC-BRB structure design.(3) Parametric investigations on the seismic performance of SC-BRB hinged frames are conducted. The results of nonlinear dynamic analysis under 20 ground motions on behalf of design basis earthquakes and maximum credible earthquake are as follows. The decrease of seismic reduction factor R can reduce the inter-storey drifts and residual storey drifts, so R is recommended to be 6 and 8 respectively for short-period and long-period structures. The increase of second stiffness ratio a can reduce the inter-story drift angles and improve the inter-storey drift distribution, so a is recommended to be 0.1-0.2. With the decrease of post-yield strength ratio β, the inter-story drift angles are reduced, yet the residual storey drifts increase. So β is recommended to be 1.0-1.62. The increase of friction active inter-story drift angle θa can reduce the residual storey drifts, so 6a is recommended to be greater as possible when the pre-tensioned tendons are guaranteed not broken.(4)Parametric investigations on the seismic performance of SC-BRB dual frames are conducted and the results are as follows. The decrease of the stiffness ratio of braced frame and moment frame aB/M can improve the weak story effect. However, if the value of αB/M is small, the inter-storey drifts and the residual storey drifts will increase. So αB/M is recommended to be 1-3. The value of R is related to αB/M-When αB/M is great, R should be decreased. The influence of a in dual frames is the same with that in hinged frame, so a is also recommended to be 0.1-0.2. The decrease of β can reduce the inter-story drift angles but has little influence on the residual storey drifts, so β is recommended to be 0.5-1.0. The increase of θa can reduce the inter-story drift angles and the damage concentration factor.(5) Aiming at the characteristics of the SC-BRB framework, the concept of dual control in the maximum displacement and residual deformation was adopted, and three kinds of performance targets to SC-BRB framework is put forward. Based on the results to the parametric analysis of seismic performance, a simplified statistical relationship between residual displacement angle and maximum displacement angle is established. Pointing at the hysteresis characteristics of SC-BRB with a friction device at the end, the calculating formula to the equivalent damping ratio is derived, and equivalent stiffness reduction method to SC-BRB structure in equivalent linearization process is established. On these basis, the direct seismic design method and process based on displacement to the SC-BRB framework is set up, the results show that the method is simple and dispense with iteration, the dual control of the maximum and the residual displacement can also be better achieved. |
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