Interaction between Cross Frames and Girders

Abstract

This paper presents a three‐dimensional finite element algorithm for computing internal forces in intermediate and end cross frames of multibeam composite steel bridges. The developed algorithm was applied to four medium‐span [137 ft (41.75 m)] simply supported multigirder tangent four‐lane bridges, with X‐type intermediate cross frames and end cross frames of the Warren truss with verticals type. One was a right bridge and the others had 20°, 40°, and 60° skew angles. It was found that: (1) Most members of the intermediate cross frames may develop compressive and tensile forces; (2) maximum compressive forces occur in the cross‐frame diagonals attached to the ends of exterior stringers, close to the obtuse angles of the bridge; (3) maximum tensile forces occur in the cross‐frame chords, at midspan; (4) the effect of skew may be neglected for skew angles of 20° or less; (5) the higher the skew angle, the higher the maximum forces induced in the cross‐frame members; (6) the larger the cross‐frame members' sections, the higher the internal forces induced in them, and vice versa; and (7) vertical deflections are not affected by the change in cross‐frame members' sections. However, the horizontal displacements of the girders' bottom flanges are reduced with the increase in the cross‐frame members' sections, and the maximum differential vertical displacements between adjacent girders occur near the obtuse angles of the bridge between an exterior girder and the first interior one.