Study On The Seismic Performance Of Eccentrically Braced Steel Frame With Self-centering Very Short Shear Links

The effective improvement of the seismic performance and seismic resilience capacity of the newly buildings is currently in higher demand to meet the modern code for seismic design.Therefore,how to effectively reduce the seismic hazard and improve the seismic performance and seismic resilience capacity has become an important part of seismic research of building structures.The energy dissipation technology is one of the most directive and effective way to achieve the high seismic performance and strong seismic resilience capacity.Eccentrically braced frames(EBFs)have been accepted as one of earthquake-resistant structural systems.The shear links in the EBFs are usually designed to allow high ductility and energy dissipation capacity during rare earthquake,and only shear links are supposed to replaced to recover the seismic performance after the earthquake.However,the shear links may experience the severe deformation and damage during the rare earthquake,and the repair processes for earthquake damaged EBFs will be considerably complicated and expensive.EBFs needs to further improve the ductility and energy dissipation capacity of the energy-dissipating section and reduce the damage as well as residual deformation of the energy-dissipating section.In this paper,an innovative self-centering very short shear link(SC-VSSL)with the self-centering SMA braces and VSSL-SSBC that has an advantage of high ductility,good energy dissipation capacity,low damage and low residual deformation is developed and used in the EBFs.The SC-VSSL will slip in shear of VSSL-SSBC and bear the axial force of SC-SMAB to satisfy the seismic requirement during the frequent and design earthquake,and all the components in the SC-VSSL will be always in elastic.During rare earthquake,the shear slotted bolted connection,very short shear link and SC-SMAB will dissipate most of earthquake input energy to reduce the seismic response of structure,and the SC-SMAB provides the restoring force,so the deformation and residual deformantion of SC-VSSL can be minimized.In this way,the new seismic design goals “No damage under the frequent and design earthquake,little damage and high seismic resilience capacity under rare earthquake”can be easily and effectively realized.This thesis attempts to gain a deep understanding of seismic mechanism and design method for an innovative eccentrically brace frame with SC-VSSL.The research content mainly consists of following aspects:(1)To summarize the background and investigative statues of EBFs,shear links,slotted boltted connection,VSSL-SSBC,self-centering steel frame,SMA,and self-centering SMA components,and the advantages and disadvantages of the above-mentioned structures or components are discussed,then the main research contents of this paper are described.(2)A comprehensive experimental investigation of the mechanical property of1.0 mm diameter SMA wires under different cyclic numbers,strain amplitude,loading rates,and initial strains is developed,then the improved Graesser model program in the SIMULINK toolbox of MATLAB are developed to simulate the hysteretic curves of SMA wires,and the accuracy of numerical results is verified by comparison with test results.(3)The basic constructs and work principle of SC-SMAB are expounded,then cyclic tests are carried on non-SMA braces specimens and SC-SMAB specimens,As a result,the hysteresis curves,skeleton curves,secant stiffness,energy dissipation capacity and self-centering ratio of these specimens can be investigated.The improved numerical model that combines with the Graesser model and Bouc-Wen model in MATLAB are used to simulate the seismic performance of the SC-SMAB.(4)Cyclic loading tests are carried on three very short shear link specimens with stiffener spacing and placing,so the failure modes,hysteresis curves,bond curves,secant stiffness,energy dissipation capacity and energy dissipation coefficient can be investigated.Finite element models,verified by comparison of tests results,are utilized to investigate the mechanical property of very short shear links,including the ratio of flange over web area,flange strength and stiffener spacing.(5)The influences of friction coefficient,bolt pretension and slotted hole of shear slotted bolted connection are analyzed by using experimental and numerial analsysis.Then the mechanical property and design method of VSSL-SSBC that combine with the very short shear link and shear slotted bolted connection can be determined by using the experimental,numerial and theoretical analysis method.(6)Based on the above-mentioned results of SC-SMAB and VSSL-SSBC,the mechanical properties of SC-VSSL are analyzed by the experimental,numerial and theoretical analysis method,the interaction and influence rule between the SC-SMAB and VSSL-SSBC are investigated,and hence the design method of SC-VSSL is established,which can provide the theoretical basis for the EBF with SC-VSSL.(7)Investigations on seismic performance of eccentrically braced steel frame with self-centering SMA brace,VSSL-SSBC as well as self-centering very short shear link are undertaken respectively,and the seismic performance and seismic characteristics of the frames and EBFs under different earthquakes are also expounded in detail,the advantages of EBF with SC-VSSL can be evaluated and summarized.