Dynamic analysis of sliding structures with unsynchronized support motions

The dynamic analysis of sliding structures is complicated due to the presen ce of friction. Synchronization of the kinematics of all the isolation bear ings is often granted to simplify the task. This, however, may lead to inac curate prediction of the structural responses under certain circumstances. Stepped structures or continuous bridges with seismic isolation are notable examples where unsynchronized bearing motions are expected. In this paper, a logically simple and numerically efficient procedure is proposed to solv e the dynamic problem of sliding systems with unsynchronized support motion s. The motion equations for the sliding and non-sliding modes of the isolat ed structure are unified into a single equation that is represented as a di fference equation in a discrete-time state-space form and the base shear fo rces between the sliding interfaces can be determined through simple matrix algebraic analysis. The responses of the sliding structure can be obtained recursively from the discrete-time version of the motion equation with con stant integration time step even during the transitions between the non-sli ding and sliding phases. Therefore, both accuracy and efficiency in the dyn amic analysis of the highly non-linear system can be enhanced to a large ex tent. Rigorous assessment of seismic structures with unsynchronized support motions has been carried out for both a stepped structure and a continuous bridge. Effectiveness of friction pendulum bearings for earthquake protect ion of such structures has been verified. Moreover, evident unsynchronized sliding motions of the friction bearings have been observed, confirming the necessity to deal with each of the bearings independently in the analytica l model. Copyright (C) 2000 John Wiley & Sons, Ltd.