Shaking Table Test On The Earthquake Mitigated Structure With Magnetorheological Dampers

As a typical representative device of semi-active control,magnetorheological(MR)damper perfectly combines the flexibility of active control and the reliability of passive control,and it can provide continuously tunable damping force with tiny energy consumption.Therefore,MR damper has received extensive attention from scholars both at home and abroad.For the reason that the MR damper mitigation system is a cross-discipline involving many fields,there are still many problems that have not been solved.In particular,the systematic exploitation and design of the damping system of MR damper,and how to realize the high integration and miniaturization of the MR damper mitigation system are less studied,and there are few researches on the real-time online control effect of the highly integrated MR damper mitigation system.Therefore,the study of the mechanical properties,magnetic field distribution,optimization design,design and exploitation of controller are carried out.The main contents are as follows:(1)Mathematical model considering Stribeck effect for MR damper is proposedThe performance test of a double rod MR damper developed by our research group is carried out under different currents,displacement amplitudes and excitation frequencies to study the hysteretic damping characteristics especially the Stribeck effect in the low velocity region.Then the reason for the Stribeck effect and its variation with current,frequency and displacement amplitude are studied.Then,an improved model based on sigmoid model is proposed to describe this Stribeck effect.Finally,the predicted forces of the proposed model are validated with the experimental data.(2)Magnetic circuit analysis and experimental investigation of MR damper based on full component modelIn order to carry out the optimal design of MR damper,the magnetic induction strength at the damping gap of a MR damper is accurately analyzed.First,the magnetic circuit of a MR damper based on a full component model is theoretically analyzed,and the computational method for the magnetic induction intensity at the damping gap of the MR damper is proposed based on the equivalent magnetic circuit theory.Then the finite element models for the MR damper with different components are established by using the general finite element software.The magnetic induction intensity at the effective damping gap is calculated,and the magnetic induction intensity under the corresponding working conditions is tested.The results show that the simulation results of the models considering the non-working magnetic circuit are in good agreement with the experimental result;The results of magnetic induction calculation based on full component finite element model are more accurate and reliable.(3)Optimal design of damper based on performance objective is realizedThe maximum damping force and adjustable coefficient of MR damper are highly dependent on the strength of the magnetic field at the damping gap and the geometrical dimensions of the damper.In order to realize the optimal design of the MR damper with specific performance,an intelligent target optimization design method for MR damper is proposed,which realizes the optimal balance between magnetic induction intensity and damper geometry at the damping gap.The MR damper was fabricated according to the optimization results,and the magnetic field test and mechanical property test were carried out to verify the effectiveness of the optimized design method.(4)Piecewise smart control strategy for MR mitigation system is proposed.Considering the reliability,stability and easy implementation requirements of the MR vibration mitigation system in practical applications,based on the balance between control effect and simplicity,this dissertation proposes a piecewise smart control(PSC)strategy based on the feedbacks of displacement and ground excitation acceleration.This control strategy makes a significant reduction in the calculative effort of the control forces,and does not need more feedbacks,and its control effect is better than the two passive control strategies,which is beneficial to the realization of the miniaturized controller,and better solves the practical application requirements of the MR mitigation system.(5)Shaking table tests on MR earthquake Mitigated Structure is carried outShaking table tests are carried out on a three-story steel frame structure which incorporates the MR damper with the micro-controller into the first floor.The dynamic responses of the real-time online intelligent controlled structure are compared with those of passive-on and passive-off controlled structures under different earthquake to evaluate vibration control efficacy of the MR mitigation system.Test results show that the MR damper mitigation system significantly reduce the vibration response of the structure and effectively realize the real-time online control of structural vibration.The comprehensive control effect on displacement and acceleration response is better than the two passive control methods.The innovations of this paper are of the followings:(1)An improved hysteresis model which can fully consider the Stribeck effect in the low velocity region is proposed.the main advantage of the model is that it can accurately describe the Stribeck effect,by a simple explicit function;(2)An intelligent target optimization design method for MR damper is proposed,which realizes the optimal balance between magnetic induction intensity and damper geometry at the damping gap;(3)A piecewise smart control(PSC)strategy based on the displacement and ground acceleration is proposed.A highly integrated MR damper vibration mitigation system is built and its vibration control effect is verified by shaking table test on model structure with MR dampers.