Seismic Performance And Design Approach Of Self-centering Damping Energy Dissipation Braced High-rise Resilient Steel Structures

The self-centering energy dissipation brace(SCB)is developed from the conventional steel brace and the buckling restrained brace(BRB).It can provide structural lateral force resistance,dissipate input earthquake energy,and reduce or even eliminate residual deformation as far as possible,resulting in the structural safety and the reduction of post-earthquake repair time and cost.This paper focuses on solving the shortcomings of existing SCBs and their structural system researches.Two new types of the self-centering damping energy dissipation braces are developed,and their hysteretic behaviors under cyclic loading are studied through theoretical analysis,numerical simulation and dynamic behavior tests.The restoring force model and simplified simulation method of the braces are proposed,and the design approach of the self-centering damping energy dissipation braces based on behavior requirements is established.A self-centering damping energy dissipation braced high-rise steel frame structure and a super high-rise steel frame-self-centering damping energy dissipation braced tube structure are developed.Through the nonlinear seismic response simulation analysis,their seismic performances and seismic resilience are studied,and the performance-based seismic design approach of the structure is established.The main research contents and conclusions are as follows:(1)A magnetorheological constant-damping self-centering brace(MR–SCB)and a magnetorheological variable-damping self-centering brace(VD–SCB)are proposed.The combination disc springs are used in their recentering devices,and the new type of smart material magnetorheological fluid is adopted for their damping devices.The dynamic behavior tests of the constant and variable damping devices were conducted under different loading amplitudes and frequencies.Results indicate that the damping devices have full hysteretic responses,and the damping forces increase as the loading amplitude and frequency increase.The MR–SCB and VD–SCB specimens with different pre-pressed forces and stiffness of the combination disc springs were designed and manufactured.The dynamic behavior tests were carried out under sinusoidal excitations with amplitudes of 3?26 mm and frequencies of 0.05?0.5 Hz.The results demonstrate that the MR–SCB exhibits a full flag-shaped hysteretic response with a high ultimate bearing capacity and a small residual deformation.Its activation force and activation deformation are stable with a symmetric behavior in tension and compression.The existence of a unique superior energy dissipation capacity results in that the pre-pressed force of the combination disc springs should only be greater than the Coulomb damping force provided by the damping device to ensure the recentering after earthquakes.The VD–SCB exhibits a full quasi-flag-shaped hysteretic response,and the combination disc springs effectively reduce the residual deformation.The brace has small activation force and stiffness sudden change when activation,an excellent energy dissipation capacity and a symmetric behavior in tension and compression.Under the premise of satisfying the bearing capacity of the brace,the pre-pressed force of the combination disc springs must be greater than the initial damping force provided by the damping device,and the appropriate stiffness of the combination disc spring should be selected.(2)The mechanical properties of the MR–SCB and VD–SCB are analyzed theoretically.Their guiding rods or outer tube and inner tubes can be divided into three and two sections,respectively.The theoretical,simulation and test results of the stress characteristics in each section are in good agreements.The low cyclic fatigue tests and failure tests of the MR–SCB and VD–SCB specimens were carried out under dynamic loading with frequencies of 0.1 and 0.2 Hz.The relative ranges of the envelope areas of half-periodic hysteretic curve and the ultimate bearing forces of the two braces are less than 6.2%,which indicates that the braces can provide stable energy dissipation and bearing capacities.After the optimization design of the non-ideal failure modes,the braces can keep excellent working conditions before the axial displacement exceeds the design value and the combination disc springs are fully compressed.The design approach of the self-centering damping energy dissipation braces based on behavior requirements is established.Through seven steps,the design parameters of the braces can be determined successively,the local mechanical behaviors should be checked,and then,the braces are completely designed.(3)A modified Bouc-Wen based restoring force model is proposed,which can describe the work stages of the self-centering damping energy dissipation braces completely and accurately.The overall stiffness of the model should be consistent with the actual stiffness in each stage of the braces.All model parameters are directly or indirectly related to the design parameters of the braces.The responses of the MR–SCB and VD–SCB specimens with different pre-pressed forces and stiffness of the combination disc springs are predicted by the modified restoring force model.The results show that the model can accurately simulate the axial force time history,force-displacement and force-velocity curves of the braces.The restoring force model subroutine of the self-centering damping energy dissipation braces is developed by using the modified restoring force model and the general finite element software LS-DYNA.This subroutine is used to simulate the hysteretic responses of the braces under seismic loading,indicating that the hysteretic behaviors of the MR–SCB and VD–SCB can be simulated well,and the results are smooth without ambiguity.(4)A self-centering damping energy dissipation braced high-rise steel frame structure is proposed.The braced exterior frame mainly bears the horizontal load,and the interior frame mainly bears the vertical load.Through the nonlinear seismic response simulation analysis,it can be found that under the strong earthquakes,the maximum average residual deformation ratios of the steel frame structures with the MR–SCBs and VD–SCBs are significantly smaller than those of the structures with the BRBs and existing SCBs.The displacement and acceleration control effects of the structures with the MR–SCBs and VD–SCBs are similar to that of the structures with the BRBs and better than the structures with the existing SCBs.The recommended values of the design parameters of the MR–SCB and VD–SCB are as follows: the activation force remains at the initial value;the activation displacement is 50% of the initial value;the ratio of the recentering to energy dissipation capabilities is 1.0 and1.0?1.1,respectively;the variable damping region of the VD–SCB is designed according to the axial displacement of the brace when the interstory drift ratio is 1%;and the viscous damping coefficient of the brace is increased appropriately.The maximum interstory drift ratio and residual deformation ratio of the structure increase with the increase of the peak ground acceleration.When the structural interstory drift ratio exceeds the elastic-plastic limit,the residual deformation ratio of the MR–SCB structure is only 0.30%.The near-field earthquake has larger velocity amplitude and longer velocity pulse period,and the influence of higher-order modes is more significant.The maximum average interstory drift ratio,floor acceleration ratio and residual deformation ratio of the structure with the VD–SCBs increase by 13.90%,11.18% and 33.25%,respectively.Combined with the damage development process of different types of components in the structure,the seismic performance of the self-centering damping energy dissipation braced high-rise steel frame structure is divided into four levels,and is quantified as the limit values of the interstory drift ratio and residual deformation ratio.In the design process,the design parameters of different components should be checked and optimized according to the quantitative limits of the seismic performance levels.(5)A super high-rise steel frame-self-centering damping energy dissipation braced tube structure is proposed.Braced tube and exterior frame constitute two seismic fortification lines of the structure.Through the nonlinear seismic response simulation analysis,it can be found that both the MR–SCB and VD–SCB tube structure can meet the performance requirements under different seismic levels.The maximum average residual deformation ratios are 0.052% at both the 39 th and 33 th stories,which exhibits a good seismic resilience.With the increase of the peak ground acceleration,the superior energy dissipation capacity of the MR–SCB makes the dissipated energy increase,hence,its control effects on the structural displacement and residual deformation become slightly better than the VD–SCB,and the acceleration control effect is close to the VD–SCB.The excellent seismic performances of the MR–SCB and VD–SCB tube structures indicate that the selection principles of the brace design parameters for high-rise braced steel frame structure are also available for the super high-rise steel frame-braced tube structure.