Hysteretic Behavior And Design Methods For A New Type Assembled Self-centering Buckling-restrained Brace With Disc Springs

Although the buckling-restrained brace(BRB)has a stable bearing capacity and good ductility and energy dissipation capacity,it is inclined to have large residual deformation under the strong earthquake,which increases the repair cost after earthquakes.In order to overcome these disadvantageous aspects,the self-centering system(SC)can be introduced into the BRB to form a self-centering buckling-restrained brace(SCBRB).At present,the commonly used materials for self-centering system are shape memory alloys or high-performance composite fiber bars or high strength steel strands.However,the shape memory alloys are expensive and their performance is susceptible to temperature.The anchoring of composite fiber is difficult and the elastic deformation capacity of high strength steel strands is limited.Therefore,a new type assembled self-centering buckling-restrained brace with disc spring was proposed in this paper.The quasi-static tests and numerical simulation were carried out to investigate its seismic performance.The main contents of this research are as follows.(1)A new type assembled SCBRB was proposed to realize that the combined disc springs in the self-centering system is always under compression when the overall brace is either in compression or in tension.The constructional details of the SCBRBs were described,and the design process and working principle of the SCBRBs were provided in detail.Based on the simplified bilinear hysteretic models of both buckling-restrained brace and self-centering system,the load-displacement formulas of the SCBRBs were deduced,the hysteretic models of SCBRB in both the first loading cycle and subsequent cycles were given,and hence the design of the specimens was carried out according to the hysteretic models.(2)The quasi-static tests of one self-centering brace,one buckling-restrained brace and three self-centering buckling-restrained brace were carried out.The results show that,compared with the buckling-restrained brace,the SCBRBs have good self-centering capacity with obvious flag-shaped characteristics in their load-displacement curves.The residual deformation of the SCBRBs is greatly reduced.Based on the fact that the working behavior of the self-centering system in each SCBRB is independent and stable,the bearing capacity of the SC part and that of the BRB part were separated for each SCBRB.The contribution of either bearing capacity or energy dissipation capacity from both the SC part and the BRB part to each SCBRB was evaluated.The energy dissipation of SCBRB is mainly provided by the BRB part.Meanwhile,the SC part of SCBRB also has considerable energy dissipation capacity and shares most of the bearing capacity of the SCBRB.(3)Finite element models for the SC,the BRB and the SCBRBs were established by the ABAQUS program,and the simulation results were compared with the test results to verify the rationality of the finite element models.The effects of main constructional details on the hysteretic behavior of the SCBRBs were investigated by the parametric analysis.The details include the size,initial preload and friction coefficient of the combined disc springs,the length,yield stress and cross-sectional area of steel core and the cross-sectional area and initial stress of stud bolts,etc.Based on the analysis results,the regression equation of the relationship between the self-centering ratio and the residual deformation,after unloading from the inter-story drift of 1/50,for the SCBRBs was provided.