Analysis and design of slab-on-girder highway bridge decks

It has been observed from test and analysis results that the differential deflection between girders in a slab-on-girder bridge deck reduces the negative bending moments in the deck slab. However, the effect of girder deflection is not considered in the traditional design method for bridge decks.;A simplified method for bridge deck analysis considering the effect of girder deflection is developed based on a closed-form analytical solution which is fine tuned with results of finite element analysis. This is based on the superposition of two analytical solutions. The first solution is for calculating the negative bending moment in a deck slab on rigid girders. This is obtained with a three-edge-simply-supported and one-edge-fixed slab subjected to a concentrated load. The second is for evaluating the positive bending moment in a deck slab induced by girder deflections. The latter is obtained with the moment-displacement relation of a two-edge-simply-supported slab subjected to a wheel load. To this end, the differential deflection between girders in a deck subjected to a single axle load is estimated with the orthotropic plate theory. With this approach, the effects of the girder stiffness and spacing, and the span length of the bridge on the maximum negative bending moments in a deck slab can be assessed. The simplified analysis method is validated with finite element models.;With the simplified analysis method, the maximum negative bending moment in a deck can be accurately evaluated based on the magnitude of the wheel load, the girder spacing and stiffness, and the bridge span length. The maximum negative bending moments in a deck tend to be over-estimated by the method recommended by AASHTO, especially for deck sections at the mid-span of a bridge where girder deflection is most significant. Design recommendations that can lead to a significant reduction of the top reinforcement in a deck slab by taking advantage of girder deflections are proposed.