Researchon Anti-seismic Performance Of Long-Span Continuous Bridge Considering Vertical Earthquake Force

As the development of the monitor techniques,more earthquakes have been recorded.Many vertical motions were detected and attracted many scholar's attention.Specially,in high intensity area and epicentral area the vertical seismicmotion even more drastic than horizontal seismic motion.Both at home and abroad,some achievement have been accomplished about the researchin horizontal isolation technique of bridge and such technique performed well in engineering practice,however,there still no good solution to vertical seismic motion.So,by combining the properties of the vertical and horizontal seismic motion and the previous research,this dissertation present a new three dimensional isolator and its effects on the seismic performances of long span continuous bridge.The main research of this dissertation are as follow:1)Based on many theses and international research in multidirectional seismic motions and multidimensional isolation technique this dissertation introduce the design of a new three dimension isolation device——high damping rubber and discspring three dimension isolation device.This device is composed of superstructure and substructure in series,the superstructure mainly consist of high damping rubber isolation cushion,and the substructure consist of discspring and viscous damper in parallel.High damping rubber isolation cushion can isolate the horizontal seismic action,and by changing the combination of the disc springs the device can also regulate the vertical dynamic property,and the vertical viscous damper dissipate vertical seismic energy.The three dimensional isolation device combine the advantages of high damping rubber,disc spring and viscous damper,and the device can possess suitable stiffness and damp by proper design.2)According to the mechanic properties of components of the device,this dissertation present the methods of mechanic coefficients calculation and numerical simulation about the three dimensional isolator.3)By using the finite software SAP2000 to establish the calculative model of a long span continuous bridge and analyzing the seismic response when the device are installed at different location,this dissertation figure out that only installing the devices at the piers is produce the best performance.4)This dissertation have compared the seismic responses among the bridge installed three dimensional isolator,the bridge installed horizontal isolator and the bridge without isolator,and have researched in the effects on horizontal seismic action caused by vertical seismic motion and the effects on horizontal isolation system caused by vertical isolation system.The result show that for the shear force in the pier bottom and the longitudinal displacement of the girder the vertical seismic motion exert slight influence on the horizontal seismic action and for the longitudinal acceleration of the girder and vertical acceleration of the midspan the vertical seismic motion amplify the horizontal seismic action,especially for the vertical acceleration.5)This dissertation have researched the effects on the seismic performance of the three dimensional isolator caused by variation of the pier anti-push rigidity,variation of the vertical stiffness of the device and variation of the damping coefficient.The result indicate that the seismic performance of three dimensional isolation device decrease as the height of the pier increase,based on seismic responses this example show the best range of the pier height is 10-20 m,and variation of the vertical stiffness have hardly influence on the shear force in the pier bottom and the longitudinal displacement of the girder,the decreasing amplitude ratio about the longitudinal acceleration of the girder and vertical acceleration of the midspan increase as the vertical stiffness decrease,and the variation of the damping ratio have hardly influence on the shear force in the pier bottom and the displacement of the girder,however,the decreasing amplitude ratio about the longitudinal acceleration of the girder and vertical acceleration of the midspan increase as the damping coefficient increase,moreover,according to the increase velocity of the decreasing amplitude ratio the most economic damping coefficient is about 5000kN·S/m.