Theoretical And Experimental Research On Seismic Performance Design Of Buildings With Pre-pressed Spring Self-centering Energy Dissipation Braces

The self-centering energy dissipation(SCED)braces not only provide stable energy dissipation capability to protect the safety of the main structure,but also provide sufficient self-centering capability to effectively reduce the residual deformation of the structures during earthquakes.The friction devices or buckling restrained brace(BRB)components are often used by the SCED braces for energy dissipation,and post tensioned tendons or shape memory alloy materials are often used for self-centering.While these kinds of SCED braces often have limitations in deformability,and their behaviors are obviously affected by temperatures.And thus,a new type of pre-pressed spring self-centering energy dissipation(PS-SCED)brace that consists of friction energy dissipation devices and pre-pressed combination disc springs with both energy dissipation and self-centering capabilities is proposed in this study.A series of low cyclic reversed loading tests are conducted to systematically analyze the hysteretic behaviors,energy dissipation and self-centering capabilities of the PS-SCED brace specimens with different design pairameters.Nonlinear restoring force models applicable for accurately predicting the flag-shaped hysteretic behaviors of the braces are proposed.And then,the design theory and method of the PS-SCED brace are developed.Additionally,typical low-,mid-,and high-rise PS-SCED braced frames are designed and modeled,and nonlinear dynamic analyses are conducted to study the seismic performance and resilience of braced frame structures under the fortification level,severe and mega earthquakes.The influences of design parameters of the brace on the structural performance are also investigated.Ultimately,the performance based seismic design method for the PS-SCED braced frame structures are developed.The main contents and achievements are summarized as follows:(1)A novel PS-SCED brace that is composed of friction energy dissipation devices for energy dissipation and combination disc springs for self-centering is developed.A series of low cyclic reversed loading tests of four brace specimens with different types of disc springs,overall lengths,and section forms are conducted.The hysteretic behaviors,energy dissipation,self-centering capabilities and the influence rules of design parameters of the braces with the same pre-pressed force of combination disc springs but different friction forces of friction energy dissipation devices are analyzed.The results demonstrate that the PS-SCED braces exhibit unique flag-shaped hysteretic curves under the low cyclic reversed loadings,and the energy dissipation capability of the brace increases with increasing friction force.A better self-centering behavior can be achieved by providing adequate pre-pressed force of the combination disc springs to overcome the friction force.Additionally,an inverse calculation method is proposed to predict the overall hysteretic responses of the brace employing the strain data of the measurable working sections of the specimen,and the hysteretic responses of the PS-SCED brace can be accurately described by the proposed method.(2)Destructive and low cyclic fatigue behavior tests are conducted to analyze the hysteretic behaviors,energy dissipation,ductilities and bearing capacities of the PS-SCED braces under large deformation cyclic loadings.Results demonstrate that the PS-SCED brace has a superior fatigue resistance,and can maintain stable energy dissipation and self-centering capabilities under large deformation cyclic loadings.The ductility,energy dissipation and self-centering capabilities of the brace constructed with a circular inner tube are better than those of the brace constructed with an X-shaped inner tube.The bearing capacity of the brace can be effectively enhanced by employing the disc springs without a bearing surface.Using the disc springs with a bearing surface,and increasing the lengths of the brace or segments of the disc springs are better for improving the ductility of the brace.In addition,the failure mode of the brace is the tensile failure of the inner tube,and the fracture occurs at the inner tube slots that used to locate the high-strength bolts of the friction energy dissipation devices.(3)The design theory and method of the PS-SCED brace are developed,and the specific design process and suggestions are provided.Based on the Bouc-Wen model,two nonlinear restoring force models are proposed that are applicable for accurately describing the hysteretic responses of the braces.Comparisons of the model prediction and test results indicate that the piecewise simplified model and the nonlinear mechanical model can effectively describe the hysteretic behaviors of the PS-SCED brace.The nonlinear mechanical model is more accurate in predicting the restoring force,smoothness of stiffness transition,equivalent viscous damping ratio and cumulative energy dissipation than that by the piecewise simplified model.The parameters of the nonlinear mechanical model that determined the energy dissipation level and stiffness of the brace have obvious effect on the hysteretic responses of the brace,whereas the other parameters controlling the shape of cycles have a little effect on the hysteretic responses,and thus,these parameters can be set to constant values to simplify the model of the PS-SCED braces with the same configurations.(4)The proposed nonlinear mechanical model of the PS-SCED brace is implemented in LS-DYNA.Typical low-,mid-,and high-rise PS-SCED braced frames with 4,8 and 16 stories are designed and modeled based on the four-level seismic performance objective of the earthquake-resilient structures,the seismic performance and resilience of the structures under the fortification level,severe and mega earthquakes are analyzed.Results demonstrate that the PS-SCED braces can reduce the interstory drifts of the structures more effectively than the conventional steel braces(CSBs),and can have the same control effects as the BRBs under the severe and mega earthquakes.The braces can effectively reduce the residual deformation of the structures due to their unique flag-shaped hysteretic behaviors,but which also make the structural accelerations slightly larger than that of the BRB frames,and the structural accelerations increase obviously with increasing contact friction between the combination disc springs.The influence rules of design parameters of the brace on the seismic performance of the buildings with the PS-SCED braces are analyzed,the performance based seismic design method for the PS-SCED braced frame structures are developed.