Research On Seismic Design Of Tall Piers For Railway Bridges

Bridges with tall piers have been widely applied in high-intensity earthquake areas in western China. Based on the characteristics of tall piers of railway bridges, seismic response of railway bridge piers is systematically studied by a combination of theoretical analysis, numerical simulation and experiments. The related problems in practical seismic design are analyzed and a corresponding seismic design method is presented. Effective improvement measures are proposed for the seismic design of the existing railway tall piers. The major work and results are detailed as follows:(1) On the basis of general tall hollow piers of railway bridges, the length of plastic hinges, failure characteristics, skeleton curve and hysteretic laws of tall hollow pier are obtained under horizontal cyclic loading. Skeleton curve and the hysteretic curve are obtained by numerical simulation methods and are compared with the experimental results. Rational ratio of reinforcement and reinforcement arrangement are presented.(2) The nonlinear beam element analysis model is established based on quasi-static model experimental results and nonlinear seismic responses of tall hollow piers are studied. Formation and development of plastic hinges are studied by incremental dynamic analysis (IDA) for tall piers. Ductility design method for tall piers is proposed based on results of seismic response. Ductility categories, energy dissipation mechanism, index and method of ductility verification for tall pier are discussed respectively. The applicability of the proposed method is verified by an example.(3) The concept of resisting small earthquakes and controlled rocking for stong earthquake is proposed on considering the importance of the tall pier in the earthquake relief and reconstruction process. A controlled rocking isolation device for tall pier is devised. Pier utilizing this device can effectively prevent earthquake damage and can be completely reset by self-weight after the earthquake. Lift-off of pier bottom is simulated by many vertical springs, which can only bear the pressure. The distributed Winkler spring model is proposed for the controlled rocking of pier. The validity of the distributed Winkler spring model is verified by a comparison with the results of shaking table test. Two-spring model for the controlled rocking of tall piers on rigid foundation is presented through the extension of the Winkler spring model.(4) Design of controlled rocking for tall pier with pile foundations is studied. Isolation effect of tall piers is analyzed in strong earthquake. The results show that the tall pier with controlled rocking of has no fixed vibrating period and isolation effect is stable and fine. The base moment of tall pier with controlled rocking is basically unchanged. The hysteretic relationship between base moment and rotation angle is inverted'Z'shape. (5) The concentrated rotational spring model is proposed for easy by designers. The concentrated rotational spring model can simulate the rocking isolation of tall pier with pile foundation by contrast with the distribution of winkler spring model.(6) Effect of steel bars for restrainers on the seismic response of tall pier with controlled rocking device is analyzed. The results show that steel bars can reduce displacement of the pier top but will increase moment of the pier base.