Research On Mechanical Behavior Of Toggle Buckling-Restrained Braces

One of the effective ways to improve the seismic behavior of the structure is to add energy-dissipation devices in the structure.Buckling-restrained brace(BRB),which is one of the metallic yielding braces with stable enegy-dissipation capacity,can significantly improve seismic performance of the structure.The existing research and application of BRB mostly use in either diagonal or chevron installation,which results that BRB can exert the function only in the case of large structural drift.At the same time,in some engineering situations,it is necessary to design BRB with high yield bearing capacity,which leads to the problem that the core area is too large,the design of the buckling restraint mechanism is complicated and the BRB manufacturing is difficult.The toggle-brace-damper can magnify the displacement requirements of the damper with the toggle mechanism that allows the story to yield at a small displacement.Moreover,the zoom capacity of BRB's yield strength and stiffness by means of toggle mechanism can be used to reduce the BRB bearing capacity requirements,thus simplifying the BRB production.In this study,based on research results of BRB and toggle-brace-damper,a new concept for BRB design:toggle buckling-restrained brace(TBRB)system has been proposed.In TBRB system,BRB is fixed near the toggle.Through the opening and closing movement of toggle-brace system,the deformation of BRB is much larger than drift,which greatly dissipates the vibration energy,reduces the structural responses and improves the seismic performance of the structure.Through theoretical analysis and numerical simulation,the main work and conclusions are as follows:(1)The geometrical relationships and displacement magnification mechanisms of TBBRB were profoundly analyzed,especially presented three new systems:upper convex toggle buckling-restrained brace(U-VTBRB),lower convex toggle buckling-restrained brace(L-VTBRB)and lower concave toggle buckling-restrained brace(L-CTBRB).Detailed formulas of the three kinds of TBRB's displacement magnification factor was derivated.The results show that:displacement magnification factor is in the range of 2.0 to 6.0,while BRB can exert the energy-dissipation function even in small structure deformation.The stiffness of TBRB system is discussed when the toggle deformation was considering.Taking the story drift ratio as a control target,the magnification factor of three kinds of TBRB under different design parameters were compared to optimize TBRB systems with good displacement magnification effect.It is concluded that all three kinds of TBRB systems under rational design have a larger magnification factor than diagonal BRB system.With same design parameters,the U-VTBRB system has the same displacement magnification effect as the L-VTBRB system,which is superior to L-VTBRB system.(2)The mechanical properties of TBRB system was also studied.By comparing the restoring force curve of TBRB system and diagonal BRB,the relationship between the core area of TBRB and the core area of diagonal BRB is obtained while TBRB system's yield force or stiffness is equal to diagonal BRB.In most cases,to achieve the same yield strength or stiffness as the BRB,the TBRB core area is smaller in size and the TBRB system can yield under smaller story drift.So TBRB system can reduce BRB size,and greatly dissipates the vibration energy under small structural deformation.By changing the geometric design parameters of TBRB,the position of the yield point on the TBRB system restoring force curve can be adjusted flexibly.To facilitate practical applications,through derivation,a procedure for determining the geometry and design factors of TBRB mechanism was established.(3)Based on the finite element software ANSYS,a numerical model of TBRBF was established.The relationship between toggle-joint's installation error and the lateral force of TBRB was studied by nonlinear static analysis,and the effect of installation error on the out-of-plane stability of TBRBF was investigated.The stability of TBRB in the process of stress was analyzed with the principle of minimum potential energy too.The results show:When the shear force causes the toggle to be tensile,with the increase of the force,the toggle-joint with out-of-plane installation error gradually returns to the original frame plane,indicating that the out-of-plane stability of the TBRBF is gradually improved.When the shear force causes the toggle to be compressed,the out-of-plane stability of TBRBF is gradually deteriorated as the force increases.In practicral applications,it is recommended to strengthen the plane stiffness of TBRB,while trying to avoid toggle-joint's installation error.(4)A toggle buckling-restrained brace(TBRB)energy dissipation system is proposed based on a super tall frame-core tube structure.According to nonlinear time history analysis,it's structural vibration responses were fully approved in ETABS program and compared with chevron BRB system.It is found that the TBRB in strengthen layer has the better control of the story displacement and story drift,and can reduce BRB size for easy installation.Therefore TBRB is particularly suitable for engineering applications where yield strength or stiffness requirements are large,such as high-rise or super-high-rise buildings.The effect of TBRB energy dissipation system has the advantages of explicit energy dissipation mechanism,high energy dissipation,little influence on function and daily use of the structure,and the study of this new form of brace is bound to play a positive role in the application of energy dissipation technology in high-rise and super-high-rise structure.