Study On Seismic Performance Of Base-isolated System With Inerter System

Base seismic isolation as a passive control technology,with characteristics that effectively mitigate seismic response,is widely used in new buildings and reinforced repair structures in high-intensity zones since the Wenchuan earthquake.Particularly,in recent years,seismic isolation technology has been promoted in primary and secondary school buildings and hospital construction.In recent strong earthquakes,characterized by high intensity,large pulse,and long duration,a survey of seismically isolated structures identified that some rubber bearings endured significant horizontal deformation and bearing uplift.Most existing built seismic isolation structures are located in high-intensity zones,and as earthquakes are occasional,random extreme events,situations may occur where the actual seismic intensity is significantly greater than the design intensity.From a seismic resilience perspective,it is necessary to upgrade the seismic target,to resist the safety reserves of the isolated structure in the event of beyond-designed or extremely rare ground motions.Therefore,this study focuses on the requirement to reduce the seismic isolation layer displacement of the base isolation structure subjected to near-fault type and far-field type harmonic ground motions.The proposed solution is based on a hybrid control strategy of the inerter-based dampers and base isolation structure for seismic performance research.Hence,the main contributions of this research can be summarized as follow.(1)A mechanical model based on the inerter-based isolation system is developed to derive an optimized parametric solution for a single degree of freedom system equipped with an seriesconfigured inerter-spring-damper system(ISD)and an optimized parametric closed solution for the ISD based on fixed point theory is obtained.This was confirmed to be equally effective for the design of multi-layer isolation systems using an example.Subsequently,three different passive vibration control system combining seismic base isolation equipped with inerter systems were evaluated,namely seismic base-isolation with ISD,seismic base-isolation with tuned viscous mass damper system(TVMD)and seismic base-isolation with tuned inerter damper system(TID).The results demonstrate that the seismic isolation layer response and the superstructure can be effectively reduced using hybrid control of the base isolation and the inerter-system,and the displacement of the isolation layer can be effectively reduced under strong earthquakes conditions.The acceleration of the upper floors of the structure can also be effectively reduced with reasonable inerter-system parameters.(2)An expression for the axial force at the end of the ball screw type inerter was developed and the factors affecting the non-linearity of the inerter were analyzed.Based on the rotary viscous damper,mass flywheel,and ball screw linear module assembled by rigid coupling,the dynamic response characteristics of the rotary viscous and inerter-based dampers were tested respectively.The damping parameters were calibrated and the dampers energy dissipation capability was verified.(3)Shake table tests were conducted based on the assembled inerter-based damper to test the damping effect of the traditional seismic isolation structure and the proposed new passive vibration control system combining seismic base isolation with inerter-based damper.The results demonstrate that the new passive vibration control strategy effectively controls the root mean square value of the absolute acceleration of the floor subjected to the far-field harmoniclike ground motions,while significantly reducing the displacement of the seismic isolation layer,which has superior engineering application prospects.(4)A comparative study was conducted involving the seismic capacity of traditional isolation structures(TIS),TIS with ISD,TIS with TVMD,and TIS with TID,considering the effect of the non-linearity of the isolation layer and the non-linearity of the superstructure on the control effect of the base isolation system with inerter system.The Bouc-Wen hysteresis model was used to simulate non-linear behavior of the rubber bearing and the superstructure,and the synergetic equations for the motion of the non-linear base-isolated system with inerter system were derived.Finally,a non-linear incremental dynamic analysis and seismic fragility assessment was conducted.The results demonstrate that the additional ISD,TVMD,and TID all significantly reduce the displacement demand of the seismic isolation bearing,as assessed from the perspective of the 50% quantile IDA curve.Improves the seismic capacity of the isolation layer under rare and very rare earthquakes conditions without significant impact on superstructure seismic capacity.From the perspective of the seismic fragility curve,the seismic base isolation system with an inerter system significantly reduces the seismic vulnerability of the isolation bearing and improves isolation layer seismic resistance under strong earthquake conditions.However,this increases superstructure seismic vulnerability.Superstructure vulnerability to near-field pulsed ground motion is more sensitive than that of far-field and near-field non-pulsed ground motion,the superstructure vulnerability curve is extremely steep,and superstructure failure is possible prior to the isolation layer.Hence,the effect of near-field pulse ground motion characteristics must be considered when using a base isolation system with an inerter system.