| Buckling Restrained Braces (BRB) have get the attention of scholars and are more and more applied to the project for its good hysteretic energy capacity. However, some problems of BRB need to be solved for wider application. Firstly, the outer restrained components of traditional BRB need perfusion mortar or concrete which consume much time and labor, these BRB can't be reused after damage. Secondly, the existing buckling restrained braces which have low fatigue life and unstable performance. Finally, the lack of a design method which considers lateral stiffness and damping ratio of BRBIn this paper, a set of BRB with all-steel combined section were designed and made by use of Q235, and high dissipative viscoelastic material proposed by our research group is served as unbonded layer on one specimen, then performance experiments were performed. Finally, in order to solve the problem of application, a simplified design method of BRB-steel frames was proposed. The main contents and conclusions of the paper are as follows:(1) A set of BRB with all-steel combined section were designed and made, the outer restrained components are able to provide great flexural rigidity, the outer constrained components were connected by bolt, which have assembled characteristics. After the destruction of BRB, the inner core can be replaced, then the BRB can continue working which act as "structural fuse". Two specimens were made, one specimen was Buckling-Restrained Brace with high dissipative viscoelastic material serves as unbonded layer (BRB-2), the other was named All-steel assembled Buckling-Restrained Brace (BRB-1).(2) The viscoelastic layer were regarded as micro-springs when the stability of inner core was checked, the formula of buckling capacity was induced and the formula indicates that the smaller thickness of viscoelastic material layer and the greater modulus of elasticity which lead to the higher buckling bearing capacity. Force analysis was carried out on the buckling half-wave of the two specimens respectively, inducing the formula of the maximum strain amplitude and then predicting the fatigue life of two specimens, analyzing the relevant parameters based on Manson-Coffin model of smooth steel specimens. The predictions indicate that:BRB-2 has a higher fatigue life than BRB-1. The parametric analysis indicate that:the bigger bulk modulus/thickness ration of the viscoelastic leads to a higher fatigue life of BRB-2; the smaller the gap leads to a higher fatigue life of BRB-1.(3) 5 kinds of frequency and 4 kinds of amplitude cycling load were applied on the two specimens, the results indicate that the fatigue life of BRB-2 is higher than BRB-1, which consistent with the theoretical prediction and the error is within 20%, indicating that the method based on Manson-Coffin model can predicate the fatigue life of BRB accurately. Meanwhile, the hysteresis curve of BRB-1 is slightly fuller than BRB-2, but the hysteresis curve of BRB-2 is flat and stable and the hysteresis curve of BRB-1 "jump" in the compression stage obviously which result in imbalance of the bearing capacity. The stability factor of hysteretic energy dissipation almost unchanged with the increase of cumulative plastic deformation, which shows high stability and symmetry of BRB-2.(4) Based on the finite element analysis software ANSYS, finite element model of BRB-1 was built with solid45, and the finite element model was calibrated with the existing experimental results. The gap between inner core element and outer restrained element which affect the performance of BRB were analyzed. Comparing the performance of BRB-2 with finite element model whose gap is 2mm, the results show that skeleton curves of finite element analysis and BRB-2 coincide well. However, the hysteresis curves of BRB-2 were flat and barely "jump" in the compression stage. The hysteretic energy dissipation and the equivalent damping ratio of BRB-2 is better especially in the large displacement amplitude loading.(5) Assuming the story displacement distribution of structure under rare earthquake, then the additional damping of BRB which adds to the structure was considered. A simplified design method of BRB-Steel Frame was proposed based on the reduction of response spectrum. A 7-story BRB-Steel Frame was designed by using the method and time history analysis were applied under rare earthquake. The results show that:the controlled structure's story drift meet the specification requirement and the lateral deformation is well-distributed which consistent with the assumed distribution. The number of plastic hinges was largely reduced and the control structure was basically in elasticity state. Therefore, the simplified design method of BRB-Steel Frames based on response spectrum was reliable and feasible. |
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