COMPOSITE DAMPING RATIO OF SEISMICALLY ISOLATED REGULAR BRIDGES

In this paper seismically isolated regular bridges are modelled as two -degree-of-freedom systems in the longitudinal or transverse direction , The equivalent linear characteristics, including the effective stiff ness and equivalent viscous damping ratio of isolation bearings, are u sed to formulate the equivalent linear theory of the seismically isola ted regular bridge. The system composite damping ratio, attributed to the equivalent viscous damping ratio of isolation bearing and the visc ous damping ratio of bridge column bents or piers, is obtained both by classical damping and nonclassical damping assumptions. The parametri c influences including those of the mass ratio, stiffness ratio, visco us damping ratio of bridge column bents and equivalent viscous damping ratio of isolation bearings on the composite damping ratio are invest igated. The composite damping ratio formulated in the study is compare d with that obtained from the modal strain energy method. In addition, the parametric influences on the system composite damping ratio of is olated bridges are compared with those of isolated buildings. Copyrigh t (C) 1996 Elsevier Science Ltd.