Study On Seismic Mitigation Principle And Performance Of Clutching Inertial Structure

In recent years,natural disasters such as strong earthquakes and typhoons have occurred frequently,seriously endangering the safety of people’s lives and property.Disaster prevention and reduction of civil structures,especially major projects,has become a national strategic demand,and improving the disaster prevention capacity of civil structures has always been a research hotspot in the field of civil engineering.The inerter has been widely studied because of its mass amplification effect,and inerterbased devices have played a good role in many aspects.Because the inerter provides considerable apparent mass,it can effectively reduce the natural vibration frequency of the structural system,which may be a good solution for the structure to effectively avoid the predominant period of the site,and also provides an idea to replace the traditional base isolation strategy.However,the larger apparent mass of the inerter will also reduce the damping ratio of the original structural system,so it will amplify the resonant response of the structure;in addition,when the structure begins to decelerate,the inerter may push the structure due to maintaining the inertia after the maximum velocity inherited from the structure,which will delay the attenuation process of the structural velocity and bring adverse force to the support of the inerter and transmission elements such as gears.In order to improve the theoretical performance of inerter,an ideal model of clutching inerter with one-way force transfer mechanism was given in existing studies,and it was pointed out that the theoretical performance of the clutching inerter is better than that of traditional inerter;however,the existing research about the clutching inerter on its seismic mitigation mechanism,simplified evaluation method,physical realization of the device and structural test verification are not sophisticated.Based on the above,this paper carried out systematic theoretical and experimental research on the clutching inerter and its structural system,which is summarized as follows:(1)The damping principle of inertial structure(IS)and clutching inertial structure(CIS)systems is revealed.The performance of inertial structure system is quantitatively evaluated through the inertance-mass ratio β;the frequency response performance of the clutching inertial system is analyzed by simulation,and the positive effect of the clutch on vibration attenuation is explained.According to the characteristics of inerter that reducing the natural frequency,the differences between the seismic mitigation effect of the inerter and other strategies are compared and analyzed through single-degree-of-freedom(SDOF)and multi-degree-of-freedom(MDOF)models,the feasibility of inerter to realize the effect of base isolation is discussed.The results show that the inerter will reduce the natural frequency of the structure,reduce the damping ratio of the structure and reduce the load input intensity,and the peak displacement resonance response of the inertial structure will be(?)times larger than that of the uncontrolled system;whereas the resonance response of the clutching inertial structure has been obviously reduced compared with the unctrolled structure.When the frequency of inertial structure is in line with that of other damping systems,it has better performance among them;under a certain inertance,the inerter can prolong the period of the structure to a certain extent,and when their basic period is the same,the inerter can be comparable to base isolation in performance.(2)The shaking table test of small-scale clutching inertial structure is carried out.The inerter damper(ID)with rack and pinion transmission mechanism,the clutching inerter damper with ratchet(CID)and the CID device with reducer(ECID)and the ECID with additional motor damping are designed;the structures employing the four devices,i.e.IS,CIS,ECIS and DECIS,were tested for dynamic response under different excitations.Based on the CIS test model,considering the influence of flywheel damping term of the device,the real model of the device is established,and the influence of flywheel damping on the performance of CIS is studied through simulation analysis and test verification.The comparison test between CIS and IS shows that CID can better control the structural resonance response and the peak response under seismic excitation;the comparative tests of ECIS and CIS show that increasing the flywheel inertia can further improve the control of the device on resonance response and peak response under seismic excitation,but it can not effectively improve the inertia capacity of the device;The comparative test between DECIS and ECIS shows that the flywheel damping term can effectively improve the inertial capacity of the device,which is also verified by simulation analysis.(3)The simplified evaluation method,and performance design method of the CIS system are established.Based on the principle of period equivalence and energy balance and statistical linearization method considering complex excitation,the equivalent linearization analysis of the CIS system is carried out,and the equivalent parameters of the equivalent linear system(ELS)is determined.On the basis of ELS,the performance evaluation of CIS based on random excitation and displacement response spectrum was carried out;the optimal layout of the device was studied in the MDOF model,the optimal layout position of shear deformed structure is determined.Based on the simplified evaluation method,the displacement-based design method of the multi-degree-of-freedom CIS are given;based on the modal reconstruction method,the equivalent linearization of the multi-degree-of-freedom CIS is studied.The results show that the obtained equivalent linear formula is simple and easy to use,and has sufficient accuracy to perform quick simplified performance evaluation.By maximizing the inertance-to-mass ratio of the key mode,it is found that the weak layer of rigidity is the best arrangement position of the general shear deformed structure.The proposed displacement-based design step can quickly complete displacement control target for a multi-degree-of-freedom structure;the proposed equivalent linearization method of multi-degree-of-freedom CIS enriches the calculation and analysis methods of multi-degree-of-freedom CIS.(4)Hybrid control strategies of time domain and frequency domain based on inerter and spring units are proposed.Based on the piecewise inertance system represented by the CIS,combined with the piecewise stiffness system,a time-domain hybrid control strategy is proposed,and the performance is analyzed.Considering the case of frequency-domain excitation,combined with the excellent performance of the inerter unit and the spring unit in high frequency excitation and low frequency excitation,respectively,a frequency-domain optimal hybrid control strategy is proposed,and the vibration transmissibility of SDOF isolation system is analyzed subjected to frequency-domain hybrid control strategy.The proposed time-domain hybrid control strategy makes up for the lack of control force of the structure in the deceleration phase under the piecewise inertance strategy;absorbs the advantages of piecewise inertance system and piecewise stiffness system,and achieves better performance than single piecewise control strategy.The proposed frequency-domain hybrid control strategy can achieve better shock absorption performance by switching the use of inerter or spring as the control unit according to different frequency domains,especially overcomes the problem that the traditional damping unit increases the vibration transmissibility after the frequency ratio is greater than(?);the frequency-domain hybrid control strategy may be a better choice for vibration systems subjected to fixed frequency-domain excitations.(5)The performance of inerter-based devices in various energy dissipated systems are analyzed.The tuned-mass-damper-inerter(TMDI)model is introduced to the storey isolation system;considered the change of the location of the isolation layer,the performance improvement effect of TMDI on the SIS at different isolation layer positions is studied,and the result shows that as the position of the isolation layer is increased,the enhancement level of TMDI is more obvious.The clutching inerter is introduced into the traditional TMD model,and the damping unit in it is replaced to form a clutching TMD(CTMD),which aims to expand the energy dissipation path of the tuned mass unit.The performance analysis and equivalent linearization of the CTMD system have been carried out,and the results have proved that the CTMD system can approximately achieve the performance of the optimal TMD to a certain extent.The effect of tuned inerter damper(TID)on improving the seismic performance of the mega-frame substructure system is analyzed,and the optimal control parameters of TID are obtained;the TID is then compared with traditional viscous damping(VD)strategy,base isolation(BIS)strategy and TMD strategy,and the scope of application of each strategy was summarized;the results showed that when the frequency ratio of the sub-structure to the mega frame fs<1,TID may be the best control strategy of them,and when fs>1,the BIS strategy works better.