| Steel frame structures are widely used in a variety of buildings,including hospitals,schools,and residences,due to their good seismic performance and ease of construction.However,previous earthquake damage results have demonstrated that steel frame structures can be severely damaged during severe earthquakes,resulting in significant residual deformation or even collapse of the structure after the earthquake,which has a significant impact on the structure’s occupancy and maintenance.To improve the seismic toughness of the steel frame structure,this study developed a new type of high-performance self-centeringing viscous device and systematically investigated the seismic performance of the new self-centering brace-steel frame structure system using a combination of theoretical analysis,numerical simulations,and experimental studies.The main research contents and conclusions are as follows:(1)A novel self-centering viscous device(SC-VHD)was developed.First,its structure,working principle and mechanical model were introduced.Its numerical simulation method and related material model were then developed using Open Sees software.Finally,a full-scale SC-VHD was designed,manufactured and tested.The results indicated that ring springs in the SC-VHD could provide the self-centering ability and displacement-related energy dissipation,and the viscous damper could provide velocity-related energy dissipation.The SC-VHD had excellent energy dissipation ability and could achieve complete self-centering,while also presenting excellent fatigue performance.The proposed numerical simulation method accurately described the hysteretic performance of the SC-VHD.(2)The parametric analysis for the SDOF system with the SC-VHD was performed.To investigate the effects of these design parameters on the seismic performance of the SDOF system with the SC-VHD and obtain their reasonable value range for structural design,the main design parameters were selected to conduct parametric analysis on the SDOF system with the SC-VHD.The results indicated that the SC-VHD could reduce nearly 30-50%of peak displacement and 80%of residual displacement.Reduction in peak displacement was achieved by increasing the viscous damper dampingξ_v,the ratio of preload to structural yielding strengthαor the ratio of loading stiffness to structural elastic stiffnessβ,whist the residual displacement could be significantly reduced by increasingα,βor the ratio of unloading to loading stiffnessγ.When the SC-VHD met the following requirements:ξ_v was at least 5%;αandβwere at least 0.1;andγwas at least 0.4,it ensured that the structure could meet the 2%peak inter-story drift and 0.2%residual inter-story drift criteria under the design basis earthquake.At the same time,the base shear of the main frame could be designed to be 0.8 times that of the conventional frame,with the same ductility demand as the conventional frame.(3)Spectral analysis was carried out on the SDOF system with the SC-VHD,and plastic displacement calculation methods were proposed.First,the effects of design parameters on the inelastic displacement ratio C_i spectrum,residual displacement ratio C_r spectrum,and strength reduction factor R_μspectrum were investigated.Then,using the statistical data,calculation equations for the corresponding spectra were proposed.Finally,three different methods of estimating inelastic displacement were proposed based on the proposed formulas.The results indicated that the inelastic displacement ratio C_i spectrum increased with the increase of ductility ratioμandγ,decreased with the increase ofξ_v,αandβ,and was essentially not affected by the post-yielding stiffness ratio(?).With the increase of(?),α,β,andγ,the residual displacement ratio C_rspectrum gradually decreased,but it gradually increased with the increase ofξ_v.The strength reduction factor R_μspectrum was less affected by the parameters of the ring springs and(?),which primarily increases with the increase ofμandξ_v.When calculating inelastic displacement,the maximum error of the C_i spectrum method was less than 8%,the error of the R_μspectrum method was usually less than 10%,and the maximum error of the equivalent linearization method could reach 20%,but most of the error was within 10%.(4)Force-based and displacement-based design methods were proposed for the steel moment resisting frame with the SC-VHD(SC-VHD frame).First,a force-based design method for the SC-VHD frame was proposed.The plastic hinge distribution and deformation mechanism of the SC-VHD frame were then investigated using numerical simulation,and a reasonable column-to-beam strength ratio was obtained.Finally,the lateral displacement profile of the SC-VHD frame was determined by taking into account the effects of various factors.Finally,a displacement-based design method was proposed based on the established lateral displacement profile.The results indicated that the SC-VHD frames designed adopting the force-based and displacement-based design methods could satisfy the design criteria of the peak and residual inter-story drift under the design basis earthquake.To achieve the strong column-weak beam mechanism,the column-to-beam strength ratio should be equal to or more than 1.8 for SC-VHD frames below 8 stories,whilst for SC-VHD frames with or more 8 stories,it should be equal to or more than 1.5.The lateral displacement profile of the SC-VHD frame was mainly affected by the number of stories and the column-to-beam strength ratio.(5)A three-story SC-VHD frame was subjected to a shake table test.First,the shaking table test was performed on a 1/3-scale three-story SC-VHD frame under the main-aftershock sequences.After that,the seismic performance of the middle to high-rise SC-VHD frames under the main-aftershock sequences was analyzed by numerical simulation.The results indicated that the test results were in good agreement with the numerical simulation results.The aftershock could amplify the dynamic response of the uncontrolled frame,and the increase in residual displacement was significantly larger than the increase in peak drift due to increased structural damage.However,this amplification effect could be effectively suppressed by the SC-VHD,as a result,the seismic response of the SC-VHD frame under the mainshock-only and main-aftershock sequences were nearly the same.With the increase of seismic intensity,the influence of the aftershock on the displacement and acceleration response of the SC-VHD frame and the uncontrolled frame became more and more significant due to the increased damage to the structure.Compared with the uncontrolled frame,the peak displacement,the residual displacement,the acceleration amplification ratios,and the base shear of the SC-VHD frame could be reduced by about 30-50%,50-80%,25-35%,and 20-35%,respectively.Besides,the SC-VHD could dissipate around 70%of the input energy.(6)The collapse and exceeding considered residual drift risk of SC-VHD frames were assessed.Based on the fragility analysis method and combined with the seismic hazard curves,the fragility analysis and risk assessment of 4-story,8-story,and 12-story SC-VHD frames with different design parameters and conventional steel frames were conducted to investigate the probability of collapse and exceeding considered residual drift under the maximum considered earthquake and during a 50-year period.The results indicated that the 4-,8-,and 12-story SC-VHD frames had acceptable low probabilities of collapse and probabilities exceeding considered residual drift under the maximum considered earthquake and during a 50-year period.Except that the probability of collapse and the probability exceeding considered residual drift of the 4-story SC-VHD frame during a 50-year period were greater than that of the conventional frame,the probabilities of collapse and the probabilities exceeding considered residual drift of SC-VHD frames under the MCE and during a 50-year period were less than those of the conventional frames,and the more the number of stories,the more obvious. |
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