Girder moments in simply supported skew composite bridges

Abstract

The evaluation of girder moments in composite bridges becomes more urgent with the trend to increasing truck loads. The method specified by the American Association of State Highway and Transportation Officials for such an evaluation depends only on the centre-to-centre girder spacing. This method does not account for skew and therefore is extremely conservative for skew composite bridges, since the presence of skew reduces the longitudinal moments in the girders. The method proposed by the Ontario Highway Bridge Design Code (OHBDC) depends on the longitudinal and transverse rigidities of the bridge in addition to the girder spacing. However, this method is limited to bridges with skew parameters less than a certain value specified in the code. In this paper, the influence of skew on the moment distribution factor is investigated. Furthermore, the influences of other factors such as girder spacing, bridge aspect ratio, number of lanes, number of girders, and intermediate transverse diaphragms on the moment distribution factor are examined. An experimental program was conducted on six simply supported skew composite steel–concrete bridge models. The finite element method was used for the theoretical analysis. Good agreement is shown between the experimental results and the theoretical results. In addition, the finite element method was employed to conduct an extensive parametric study on more than 300 prototype composite bridge cases. The data generated from the parametric study were used to deduce expressions for the moment distribution factor for OHBDC truck loading and for dead load. An illustrative example is presented. Key words: bridges, codes of practice, composite, distribution, moment, reinforced concrete, skew, structural engineering, tests.