Research On Hysteretic Performance And Design Method Of A New Type Assembled X-shaped Buckling-restrained Brace

The configuration of buckling-restrained brace(BRB)mainly includes diagonal,chevron and V-shape nowadays.The details and working mechanism of middle connections of X-shaped buckling-restrained brace(XBRB)are relatively complicated,and therefore only a few research and application has been conducted on the XBRBs.Nevertheless,the X-shaped BRB has the advantages such as large lateral rigidity and the two braces along two directions providing lateral constraint for each other to enhance overall stability of the compressive brace,etc.In this paper,core-separated configuration is used to design an assembled X-shaped BRB with reasonable configuration and working mechanism.The quasi-static tests and finite element analysis were carried out to examine the hysteretic behavior of the X-shaped brace.The main research contents are as follows.(1)An assembled X-shaped buckling-restrained brace,with the configuration of separated encased plate braces,was designed.Two encased plate braces are not connected at middle of the overall brace,the encased brace in each direction is offset by a half of the thickness of the plate brace from the center,the X-shaped restraining members is pre-welded at each side,and all parts are assembled together fo form an overall X-shaped brace by high-strength bolts.(2)Quasi-static tests were carried out on the designed three diagonal and six X-shaped BRBs.The test results show that the bearing capacity of two braces in each X-shaped buckling-restrained brace is relatively uniform,and both diagonal and X-shaped BRBs have full hysteresis curves with good ductility and energy dissipation capacity.Except for the local flexural failure of restraining member due to large distance of the bolts,the low cyclic fatigue faiure of encased brace with tension fracture occurred eventually.The test results also showed that the X-shaped steel plate braces encesd in the wall panel by arranging the auxiliary steel tubes around the brace with profiled sheets also have good ductility and energy dissipation capacity.(3)Using the ABAQUS program,finite element analysis models of diagonal and X-shaped specimens were established,and comparison analyisis between the simulation and test results was done to verify the feasibility of the simulation models.The parameter analysis by varying the length of brace,the size and the yield stress of constraining steel tube,the thickness and width of plate brace,etc.was conducted to investigate the overall stability and the local bearing capacity of the specimens.In terms of overall stability,the elastic buckling analysis was first used to acquire the calculated length coefficient of the diagonal and X-shaped BRBs,and then the formulas for the calculation of the overall stability bearing capacity of the diagonal and X-shaped BRBs were obtained.The formulas above were verified at last by the nonlinear analysis.In terms of local bearing capacity,the waveform of encased brace with multi-wave flexural buckling deformation was classified according to the nonlinear analysis,and the formulas to calculate half-wavelength,as well as the formulas to calculate the lateral compression force applied on the restraining member by the encased brace,were provided.Analysis models and calculation ways to check the tensile yielding of high-strength bolts and local flexural failure of the restraining members were given.