Distortional Loads and Brace Forces in Steel Box Girders

Torsional behaviour of curved composite beams in construction stage and diaphragm effects

“…In this method, the sectional bending moment of the curved open box beam produced by the vertical load is expressed as a pair of equal axial forces with opposite directions, which act in the upper and lower flanges, respectively [6]. Taking an infinitesimal element ds of the lower flange of the steel girder as the study object, when the bending moment is positive, the tangential tension forces at both sides of the bottom flange of the element are not equal due to the effect of the curvature, so the lateral force (M/(rh)) that is perpendicular to the axis and towards the inside of the curve is induced, as shown in Fig.…”

“…The lateral braces were modelled by means of virtual steel plates with an equivalent thickness, so as to transform the open U-shaped steel girder to the so-called "quasi-closed box girder" [3,4]. Fan and Helwig conducted detailed analyses on the mechanical mechanism of the lateral bracing systems and the internal cross frames, which proposed a fundamental theory for the subsequent research [5,6]. By using the finite element (FE) method, Kim and Yoo [7] proposed a calculating method for the internal force within K-type transverse braces in box steel girders, afterwards the bending behaviour of the semi-closed trapezoidal box section with X-type internal braces was studied by Kyungsik and Chai [8], and the matrix solution to the internal force of the braces was presented.…”

Bending behaviors of quasi-closed trapezoidal box girders with X-type internal cross-frames

“…The webs in the box girders have negligible resistance against lateral bending of the top flanges. (3) No solid diaphragms are provided in the box girder other than at the supports. Additional member forces developed in bracing members in the panels adjacent to interior supports due to the solid diaphragm are evaluated separately and superimposed to assess the total brace forces acting on the members adjacent to the internal supports.…”

“…Several different approaches to estimating the forces in lateral bracing members and internal cross frames of quasi-closed steel box girders have been suggested in recent years [2,3,[5][6][7]. This study examined steel tub girders with a single-diagonal-type top lateral bracing system and internal X-frames subjected to bending action.…”

“…Fan and Helwig [2,3] made a considerable contribution to the understanding of the mechanics involved in lateral bracing systems and internal cross frames in quasi-closed box girders. After deriving general form equations for estimating the forces in both crossed diagonal type and single-diagonal-type lateral bracing systems induced by vertical bending and applied torque [2], bracing system.…”