Deck modeling for seismic analysis of skewed slab-girder bridges

Seismic analysis of slab-girder single-span skewed bridges is greatly simplified if one can assume the concrete deck to be rigid in its own plane. In effect, the deck can be replaced with a rigid bar and this will eliminate many degrees of freedom associated with the superstructure. In this study, the importance of this modeling assumption, in conjunction with AASHTO’s seismic analysis methods, is highlighted. Furthermore, to investigate the effect of this assumption on analysis, a parametric study is performed on bridges with skews ranging from 0 to 60 degrees and with spans up to 30 m. It is assumed that the bridges are elastically supported with elastomeric or pinned bearings in the longitudinal direction, and cross-frames in the skew direction at each end. Linear finite element response spectrum dynamic analysis is performed on bridges with decks modeled as rigid and flexible shell elements. The effects of deck stiffness on the translational and torsional periods of vibration are noted. Stresses for flexible decks are evaluated and shown to be negligible. Seismic demand on supporting elements with rigid and non-rigid decks are compared. It is shown that the rigid deck assumption simplifies the analysis and is valid for practical ranges of slab-girder bridges.