Theoretical And Experimental Study On Rate-dependent Mechanical Model Of High Damping Rubber Bearings

Seismic isolation has been widely utilized in the civil engineering practices to protect the structures from the damage of earthquake.Recent strong earthquake events,such as those in Kobe(1995),Wenchuan(2008)and Lushan(2013)have revealed favorable examples that show the effectiveness of seismic isolation in significantly improving the earthquake resistance of structures.Among various types of isolation devices,laminated rubber bearings,including natural rubber bearings and lead rubber bearings,were mostly used in the past decades.In recent years,an evolving type of laminated rubber bearings was invented,named as high damping rubber bearings(HDRBs).Due to the addition of chemical agents,the high damping rubber possesses high damping property,therefore,the HDRBs can endow a structural system with enhanced damping and elongation of its natural fundamental period,resulting in a reduction of its seismic response without environmental pollution.Because of the abovemetioned advantages,the HDRBs have aroused worldwide attention from the researchers and have been increasingly utilized in recent major civil engineering practices.The mechanical behavior of the HDRBs is strongly nonlinear and rate-dependent,few constitutive models of the HDRBs can capture these behaviors accurately.In this study,a rate-dependent constitutive model of the HDRBs was developed based on the rubber material property,and the influence of rate-dependent behavior of rubber bearings on the comprehensive seismic response of the global isolation system was also experimentally and analytically studied at the structural level.The main contents of this study are summarized as follows:(1)A rate-dependent constitutive model of the HDRBs was developed based on the rubber material property.This model splits the total stress of the HDRBs into rate-dependent part and rate-independent part.It consists of two hyperelastic springs and a nonlinear dashpot,which can be utilized to accurately characterize the rate-dependent property of the HDRBs.(2)On the basis of multi-step relaxation tests and cyclic shear tests of natural rubber and super high damping rubber,a generalized rate-dependent constitutive law for three kinds of rubber bearings was proposed.(3)An improvement of traditional real-time substructure test system was achieved from the prospective of both hardware and control method.A new real-time substructure test system based on the velocity-control loading concept was utilized to experimentally probe the influence of rate-dependent behavior of rubber bearings on the comprehensive seismic response of the global isolation system.(4)The newly proposed rate-dependent analytical model and the traditional rate-independent bilinear model for rubber bearings were used in the numerical simulation,comparison of the simulated results indicated that the proposed model performed better than bilinear model in the seismic response analysis.(5)A rate-dependent constitutive model of the HDRBs including the consideration of vertical compressive load was developed.With the help of ANSYS software and its secondary development platform,a preliminary study was conduct to investigate the seismic response of isolated building under the far-field and near-fault earthquake ground motions with different mechanical models of the HDRBs.