Effects of the restrainer upon bridge motions under seismic excitations

Dynamic responses of a multi-span simply supported bridge retrofitted with cable restrainers between longitudinally adjacent girders are examined under seismic excitations. A simplified and idealized mechanical model is adopted and the corresponding analysis tools are developed to examine the effects of restrainers, in which the nonlinear behavior as well as the fracture of the cable are considered. Using the proposed model, the effects of the cable length, the stand-by clearance length, and the stiffness of the restrainer upon the global seismic behaviors are verified. The variations of the pounding forces between adjacent girders are evaluated to see the overall effect of the application of restrainers, and the corresponding shear forces and bending moments on each pier are investigated. The main effect of restrainers upon global bridge motions is found to constrain and redistribute the relative distances between adjacent vibrations units. It is also found that the cable length, clearance length, as well as cable section area should be selected properly depending on the level of seismic intensity.