Numerical Study On Seismic Performance Of The Structures Attached With Nonlinear Eddy Current Dampers

Vibration control technology can be applied effectively to reduce the structural seismic response.Passive control has been widely utilized in vibration control of civil engineering because of its merits of constructional simplicity and independence of external energy.Viscous damper,a type of passive energy-dissipation devices,has been previously utilized in engineering structures.Even though it has outstanding mechanical properties and excellent damping effect,it has insuperable defects such as potential oil leakage risk and high maintenance cost.Eddy current damping technique can overcome the shortcomings of viscous dampers greatly,and thus it is gradually applied in the vibration control of large civil engineering structures.However,eddy current damping has strong nonlinearity which is significantly different from viscous dampers.Therefor,this paper adopts the method of combining theoretical analysis and numerical simulation to carry out deterministic,stochastic seismic response analysis and probabilistic seismic fragility analysis for the structure attached with eddy current dampers,and study the effect of eddy current damping’s nonlinearity to structural seismic performance.The main research contents and conclusions are as follows:(1)Based on the equivalent principle of energy consumption,the equivalent linear damping ratio formula of the eddy current damping structure is derived,the nonlinear dynamic characteristics of the eddy current damping are investigated,and the relationship between eddy current damping parameters and structural response has been extensively studied by seismic response spectrum analysis.More importantly,the influence of nonlinear properties of eddy current damping on the seismic performance of multi-degree-of-freedom structures is investigated.The research results reveal that the equivalent linear damping ratio of eddy current damping is related to its damping parameters and displacement amplitude,and there is an extreme value about the critical velocity ratio;the extent of nonlinear effect for eddy current damping on the structure can be determined by two parameters mutually independent dimensionless quantities: structure damping ratio and critical velocity ratio;when the additional damping ratio is not large,the nonlinearity of eddy current damping is conducive to reducing the seismic response,and the peak value of damping force can be reduced by 40%.(2)The Stochastic Linearization Technique(SLT)is applied to study the dynamic characteristics and seismic performance of the nonlinear eddy current damping-single degree of freedom system.Based on force-based equivalence principle and the energy-based equivalence principle respectively,the relationship between the nonlinear eddy current damping parameters and equivalent linear coefficients is established,and the assumption of nonGaussian distribution is proposed to consider the influence of the nonlinear eddy current damping on the system response.The SLT results are verified by Monte Carlo simulation,and the eddy current damping parameters are optimized for different vibration control objectives.The research results show that the Gaussian distribution SLT is closer to the real results when the peak damping force of eddy current damping is small or the critical velocity is large,while for high peak damping force and low critical speed,non-Gaussian distribution SLT can better reflect the actual situation;the nonlinear characteristics of eddy current damping are beneficial to reduce the displacement response of the system,but it is not benefit for the acceleration response reduction.(3)Based on the OpenSees simulation platform,the reinforced concrete frame finite element model is established,and the difference between the centralized plastic element and the distributed plastic element is compared and analyzed.The rationality of the modeling principle is verified by comparisons with the experimental tests.The Eddy Current Damper Material is developed in OpenSees,and the development is testified by Matlab program to be accurate.Multiple working conditions of eddy current damping structure are designed and elastic-plastic time history analysis are performed.The research results show that the eddy current dampers can effectively reduce the structural response,while increasing the velocity amplification factor can further improve the seismic reduction ratio;under the rare earthquakes,the seismic reduction ratio of the interstory drift ratio and floor acceleration response reaches17%;under the rare earthquakes,increasing the velocity amplification rate to 1.5 times can increase the seismic reduction ratio of the interstory drift ratio to 1.7 times,but has no significant improvement on the floor acceleration response;increasing the velocity amplification rate to 1.5 times can improve the eddy current additional damping ratio from 5%to 10%.(4)Based on Incremental Dynamic Analysis(IDA),the probabilistic seismic fragility of the structure attached with a type of eddy current damping-rack and gear wall(ECD-RGW)is studied by finite element simulation.The probabilistic seismic demand model is established,and the effect of nonlinear eddy current damping on the seismic performance of the structure.The research results indicate that: installing ECD-RGW can significantly reduce the transcendence probability of each damage state of the structure,which can effectively reduce the probability of structural damage;under frequent earthquakes,installing ECD-RGW can reduce exceeding probability of the structure remaining intact from 28.91% to 3.05%;under rare earthquakes,installing ECD-RGW can reduce exceeding probability of the structure reaching moderate damage from 28.91% to 3.05%.