2015 CSCE Annual Conference Regina - Building on our Growth Opportunities Conference
Dr. Khaled Sennah, Ryerson University
Dr. Ghrib Faouzi, University of Windsor
Canadian Highway Bridge Design Code (CHBDC) and AASHTO-LRFD Bridge Design Specifications allow cross-frames to be parallel to the skew angle if less than 200. However, for skew angles greater than 20°, both design specifications require the cross-frames to be perpendicular to the longitudinal axis of the girder. Literature review showed that the effect of cross-frames layout in skew composite concrete slab-over steel I-girder bridges on load distribution among girders is as yet unavailable. In this paper, three cross-frame layouts commonly used in skewed bridges are considered, namely: parallel cross frames to the skew support lines (parallel layout), perpendicular cross-frames to the skew support lines (perpendicular-continuous layout) and perpendicular cross-frames to the skew support line with staggered arrangement between girders (perpendicular-discontinuous layout). A three-dimensional finite-element modelling was conducted to determine the magnification factor for moment and shear in bridge girders with different skew angle, cross-frame layout and stiffness, span length, number of design lanes and truck loading conditions. The finite-element results are presented in terms of cross-frame forces at bridge supports, differential vertical displacement of cross-frame at obtuse corners, girder longitudinal bending moment and vertical support reactions. Results showed that parallel cross-frame layout can be used for skew angles up to 300. Also, skew bridges with perpendicular-discontinuous cross-frame layout exhibited better structural performance than the perpendicular-continuous cross-frame layout. Moreover, results showed that the maximum positive moment in exterior girder is located at the girder mid-length for right-angle bridges while this location shifts towards the obtuse corner with increase in bridge skewness.