| Structural vibration control is an effective design strategy to enhance structural performance against earthquake and mitigate seismic response,which has been verified in the practical engineering.Passive energy dissipation is a comparative mature technology which has been widely used in earthquake engineering due to its simple configuration,low cost,easy maintenance and reliable run without power support.However,current technologies present some limitations,such as problems related to aging and durability,residual displacement, substitution after strong events,among others.Recently,the increasing research and development of smart materials and controlling devices open up a new area for seismic vibration control of structural engineering,providing a basic platform for the design and exploration of new generation high-performance passive damping devices.Shape memory alloys(SMA) are a class of novel smart materials that possess unique properties,including shape memory effect,superelasticity effect,extraordinary fatigue resistance,high corrosion resistance and damping characteristics,which make them perfect candidates for seismic energy dissipation devices in structural engineering.This thesis focuses on the use of superelastic SMA-based energy dissipation system for structural vibration control.Extensive investigations on the mechanical behavior of superelastic SMA wires by cyclic tensile tests,improvement of the constitutive model for superelastic SMA,design and performance test of innovative SMA dampers,analysis and optimization of energy dissipation system based on SMA damper and structural vibration control using SMA damper subjected to earthquakes,are carded out.The main contents are included as follows:(1) Cyclic tensile tests on superelastic NiTi SMA wires with three diameters were carried out.The effects of the different loading conditions,namely:cyclic loading-unloading number, strain amplitude,loading frequency and ambient temperature,on the mechanical behavior described by some fundamental quantities,such as energy dissipation per cycle,secant stiffness,equivalent damping,residual strain,were examined.The temperature changes of the SMA wires due to the latent heat under different loading conditions are analyzed.(2) According to the test data,a novel constitutive model of superelastic SMAs based on the Graesser and Cozzarelli's model is proposed,which is capable of describing the martensitic hardening under large amplitudes and the strain-rate dependent hysteretic behavior at different strain levels.An iterative procedure to determine parameter values of the improved model is proposed.To verify the effectiveness of the proposed constitutive model, comparisons between experimental and numerical results predicted by the proposed model were conducted.(3) An innovative telescopic recentering SMA damper(TRSMAD) was proposed by utilizing both the high damping and recentring features of superelastic SMA wire.The mechanical behaviors of the damper under various cyclical loading-unloading conditions with different pre-strain,displacement amplitude and loading rate were investigated experimentally. One-dimensional theoretical model based on plastic theory for TRSMAD was developed and the numerical simulation for the mechanical behaviors of the damper was performed by means of the developed model.(4) An innovative hybrid shape memory alloy friction device(HSMAFD) which consists of pre-tensioned superelastic SMA wires and friction devices(FD) was proposed.The most important property of the HSMAFD is the integration and unification with stable large energy dissipation capacity provided FD and re-centering feature profited from the superelastic pre-tensioned SMA wires.To investigate the mechanical behaviors of the damper as a function of pre-displacement,displacement amplitude,friction force and loading frequency, cyclic tensile tests on a scale model under various loading conditions were conducted.The theoretical model for HSMAFD was developed and the numerical simulation for the mechanical behaviors of HSMAFD was conducted.(5) The optimization of the parameters as well as nonlinear analysis of the energy dissipation system with SMA dampers was performed.Using energy balance method,the parameters of the SMA damper-based energy dissipation system were optimized,and the reasonable value ranges for the parameters were suggested.The dynamic equations of the symmetrical and eccentric structures with SMA dampers under earthquakes were developed and nonlinear time history analysis program for the energy dissipation system with SMA dampers based on MATLAB software was compiled.Then,as examples,two SMA damper-based frame buildings with or without eccentricity subjected to earthquake ground motions were analyzed to assess the effectiveness of the SMA dampers in reducing the structural seismic response.(6) Shaking table tests on a reduced-scale symmetric steel frame model with and without SMA dampers were carried out to verify the effectiveness of the SMA damper-based energy dissipation system in reducing translational response of structures subjected to strong seismic excitations.A 1/4-scale,3-story symmetric steel frame model of building was designed.One TRSMAD and HSMAFD were installed in the bottom story of the model,respectively.The building model with and without SMA dampers were tested through shake table.The energy analysis method was also utilized to evaluate the distribution of energy for the energy dissipation system.The experimental results show that the SMA dampers can effectively suppress the translational response of symmetric buildings.(7) To verify the control effect of SMA dampers in reducing torsion coupled response of eccentric buildings,shaking table tests on a reduced-scale eccentric steel frame model with and without SMA dampers were performed.A 1/4-scale,3-story steel frame model of building with eccentricity was designed.One TRSMAD and HSMAFD were installed in the bottom story of the model,respectively.The building model with and without SMA dampers were tested through shake table.The experimental results indicate that the SMA dampers can effectively reduce the torsion coupled response as well as translational vibration of symmetric buildings. |
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