Effect Of Effective Yield Length Ratio On Long Stroke Buckling Restrained Braces Support

Buckling-restrained braces(BRBs),as a metal energy dissipating element,not only play the role of ordinary bracing,but also have stable hysteretic behavior,strong energy dissipation and good low circumferential fatigue.In recent years,buckling-restrained braces have gradually become a hot spot for bridge engineering seismic reduction,with good development potential and application prospects.In order to meet the characteristics of large bridge seismic deformation,the flexural restrained brace needs to increase the effective yield length and at the same time meet the requirement of strong energy dissipation.Combining with the theoretical analysis,this paper proposes a long-stroke flexural restrained brace,which improves energy dissipation by increasing the effective yield length ratio with the same total brace size.The research is carried out from theoretical analysis,proposed static test,and nonlinear numerical simulation,and a reasonable scheme and arrangement form is designed on the bridge to make the longstroke flexural restraint brace give full play to the energy dissipation performance on the bridge.The main work is as follows.(1)The literature research on buckling-restrained braces at home and abroad is conducted and the research results are summarized.The development and engineering applications of flexural restraint bracing are sorted out and the theoretical analysis of flexural restraint bracing is mastered,laying the foundation for the subsequent research work.(2)Consider the influence of gap,width-thickness ratio,unbonded material,and initial bending of core material on flexural restraint support,clarify the range of parameter taking values,and develop and design the test program(including total dimensions,section form,end configuration,etc.).And the design bearing capacity and weak axis moment of inertia of BRBs are calibrated and checked to meet the design requirements.(3)Proposed static tests were conducted for two sets of long-stroke flexural restrained supports with effective yield length ratios of 0.56 and 0.68.The test phenomena and damage states of the two sets of flexural restrained brace specimens are described in detail.The hysteresis curves were processed to obtain the skeleton curves,strength degradation,ductility,and dissipation capacity for comparative analysis.The results showed that both groups of specimens exhibited good hysteresis performance.The effective yield length ratio has a significant effect on the seismic performance of specimen BRB.The effective yield length ratio will increase the ultimate bearing capacity,ultimate displacement and dissipation coefficient,strengthen the displacement ductility and dissipation capacity,and have little effect on the stiffness degradation.(4)Numerical simulations of the material nonlinearity and geometric nonlinearity of the long-stroke buckling restrained support are carried out using solid cells.Using the finite element software ABAQUS platform,the concrete damage plasticity model(GDP)and the steel intrinsic model were selected considering the initial defects.The correctness of the finite element simulation method is verified by comparing with the flexural restrained bracing tests in the literature.And the feasibility of the model is verified by comparing with the tests in this paper,which are in good agreement.(5)Parametric expansion analysis was performed by finite element model for six groups of BRBs with effective yield length ratios of 0.52-0.72.The hysteresis curves and seismic indexes such as maximum tensile to compressive ratio and energy dissipation capacity are compared to further investigate the effect of effective yield length ratio on the seismic performance of long-stroke flexural restrained bracing.