SHAKE TABLE TESTS AND NUMERICAL MODELINGOF SEISMICALLY ISOLATED RAILWAY BRIDGES

摘要

In the implementation of seismic isolation system to railway bridges, the basic requirements are asrnfollows. The first is to secure the running safety of trains under occasional earthquake (Level 1) groundrnmotion. For this purpose, the isolation bearings should work almost like fixed hinges not to allow largerndisplacement. The second is to protect bridge piers from severe damage under rare earthquake (Level 2)rnground motion. For this purpose, the isolation bearings should play their roles effectively to add flexibilityrnand damping capability to railway bridge systems. It is also expected to come back to the original positionrnafter severe earthquake motion is over, to maintain the function of the train operation. To satisfy abovernmentioned requirements, accurate estimation of dynamic behavior of the seismically isolated bridgernstructures is necessary. Especially, complicated constraining force from the railway track to the bridgesrngirder has to be accurately investigated and modeled. For this purpose, shake table tests of partial modelsrnof railway bridge structures are conducted subjected to different types and levels of earthquake groundrnmotion. The direct measurement of the constraining force to the girder is almost impossible, so, in thisrnstudy, it is detected from the equilibrium of dynamic motion of the system using displacement andrnacceleration data of the tests. The nonlinear and non-symmetric constraining force is found first time inrnthis field. The numerical models are proposed based on the experimental results. The numericalrnsimulation of the isolated bridge structures with the proposed models agrees with experimental resultsrnfairly well, suggesting that the proposed models can be used for structural design process for newrnconstruction and seismic retrofit of existing railway bridges.