Study On Self-centering Steel Link Beams Based On Shape Memory Alloy

Link beam is an energy-consuming beam in earthquake-resistant structures such as eccentrically braced frames and coupled shear walls.They dissipate energy through plastic deformation during earthquakes,but plastic deformation cannot recover after earthquakes,making it difficult to repair structures after earthquakes.For the above reasons,the academic community has proposed the concept of self-centering link beams.In the self-centering link beam,the steel link beam does not undergo plastic deformation during the earthquake,but it provides certain energy-consuming capacity by embedding dedicated energy-consuming and self-centering components,and at the same time provides restoring force to restore the structure to the near-initial state.Among them,self-centering steel link beam systems based on shape memory alloy is newly proposed.This thesis proposes two kinds of self-centering link beam systems based on SMA rods,establishes a theoretical analysis model,and deduces the load-deformation relationship,providing a basic model and method for the theoretical calculation and design of the self-centering link beam systems.In this thesis,the study of SMA rod properties was carried out,and tests are carried out to investigate the effects of heat treatment parameters,loading rate,strain amplitude,cycle number,and process sequence on the mechanical performance include stress-strain curve of SMA rods,energy consumption per unit volume,equivalent damping ratio(EVD),residual strain,forward transformation stress,and elastic modulus(EA).The analysis results show that the optimal pretreatment for the dog-bar rods with a diameter of 14mm is heating in 350? for 30 minutes and then quenching in pure water.After the above treatment,these rods has a full stress-strain curve,good energy consumption,obvious phase change steps,maximum recoverable strain of up to 5%,and stable mechanical properties.According to the experimental results,the SMA simplified stress-strain model for numerical analysis was obtained.This thesis conducts finite element simulation on the constitutive model of the SMA rods and the self-centering steel link beam based on shape memory alloy.The simulation results show that all components except the SMA rods are in the elastic range for self-centering steel link beam systems based on shape SMA.Superelastic SMA rods can restore the link beam to the initial position and can provide a certain energy dissipation capability under cyclic loading.In this thesis,two kinds of self-centering steel link beam systems based on SMA rods are studied by pseudo-static test.The test mainly analyzes self-centering capability,hysteretic energy consumption capacity,stiffness,bearing capacity,deformation capacity,failure mode,strain history of SMA rods,distribution of strain on steel link beams,etc.Then,the comparison between the finite element simulation results and the test results is conducted,and mainly compare the difference between the deformation shape and the force-opening angle curve.Finally,this thesis analyzes the reasons for this result.The results show self-centering steel link beams based on SMA rods,when the load is zero,the opening angle returns to the closed state,which means that self-centering capability is better.At the same time,because the SMA rod in the link beam still has some residual deformation,which causes the prestress relaxation,the initial stiffness of the system cannot be completely restored to the state before loading.Therefore,when self-centering steel link beam systems based on SMA rods is applied,it is necessary to pre-tightened the SMA tension bar after the earthquake to ensure the initial stiffness of the structure.