The shear stiffness of an elastomeric bearing plays an important role in the transfer of seismic forces from the superstructure to the substructure. This paper investigates the effects of this flexibility on the free vibration of skewed bridges. Slab-on-girder, single-span bridges with skew angles ranging from 0 to 60 degrees are considered. It is assumed that the bridges have cross-frames at the ends. The mass or span of the bridge is also considered as a parameter. Analytical formulation for the free vibration is compared with finite element model using SAP2000 program. It is shown that the modes of vibration are coupled and depend on cross-frame stiffness as well. It is concluded that for the usual elastomeric stiffness the first period varies but the second period is constant. It is also shown that in an actual earthquake, such as El Centro, seismic demand depends on the frequency content of the earthquake. In general, the demand goes down in the longitudinal direction and up in the transverse direction as skew angle increases.

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