Study On The Isolation Performance Of Triple Friction Pendulum Bearings Used On Low-tower-cable-stayed Bridge Under The Near Fault Ground Motion

As a new type of antivibration bearings,Triple Friction Pendulum Bearings System(TFPS)can be applied to different isolation system combination between stiffness and damping,so it can be better used in low frequency and high energy place(especially near fault)for its obvious characteristics seismic isolation design of various structures under the earthquake excitation.On the basis of the previous research results,in this paper,using single friction pendulum bearings(FPS)and gap element(GAP)model established TFPS bearing finite element analysis model,using Midas/civil software to add TFPS support of extradosed cable-stayed bridge in the face of different PGA,PGV/PGA,the site characteristic period,magnitude,pulse cycle,fault mechanism and fault distance 30 near fault seismic isolation performance study.As a contrast,this paper also studies the isolation performance of TFPS supported short tower cable-stayed bridge under 5 far field earthquakes.The results show that:(1)The addition of TFPS isolation bearing can obviously change the self vibration period of the structure of the short tower cable-stayed bridge,and prolong the occurrence time of the main vibration modes of each order of the structure.(2)Using the boundary of nonlinear time history analysis,This paper extracted the forcedisplacement curve of the support and the time-history curve of bearing shear of the pier,not only the two case history response shear amplitude is large,and almost of the large displacement and velocity pulse duration of pier shear force response was also drain by the support.the different stress that TFPS bearing can maintain its isolation performance when it faces different ground motions.(3)Through statistics the relationship of the isolation rate of the action of 30 near-fault,seismic direction,PGA,magnitude,PGV/PGA,characteristic period,fault distance and pulse cycle ground motion between the relationship of the top and the bottom shear force and the displacement of the pier are found,regardless of location,direction and magnitude of ground motion,PGA,PGV/PGA,the characteristic period of the ground how to change,the shear isolation rate was more than 60%.Generally speaking,the shear isolation capacity of TFPS support pier top can remain "no difference",but the moment isolation rate of pier bottom increases with the increasing of PGA,PGV/PGA and magnitude,and decreases with the increase of characteristic period and fault distance,however,with the increasing of PGA,PGV/PGA and magnitude,the rate of seismic isolation at the bottom of the pier keeps increasing,but with the increasing trend of the characteristic period and the increase of the fault distance.Bowever,the corresponding relationship between the above parameters and moment or shear isolation rate of the pier can not be summed up.Separate consider the 4 cases of appearing negative numbers,and the results show that the occurrence of poor seismic isolation rate is mainly ground motion with obvious fault activity,longer period of feature or longer period of rise of response spectrum.It is suggested we should consider the site design,seismic acceleration and fault spacing and fault activity history mainly when designing TFPS bearing,but for pulse period,fault mechanism and site characteristic cycle,we should consider it appropriately.(4)The 5 far ground motion is similar to the near fault ground motion with low isolation rate of TFPS bearing.for its response spectrum is rising for a long time,the isolation effect is poor.