Behaviour of unpropped composite girders curved in plan under construction loading

Composite steel and concrete curved bridges are often used in highways, particularly for motorway interchanges where high speeds require smooth changes in direction. A composite steel and concrete curved bridge often consists of horizontally curved steel girders and concrete deck slabs. The use of steel I-section curved girders is commonplace because of their economy and ease of construction. During construction, the curved steel girder carries a uniformly distributed load, comprising its self-weight and the wet concrete deck. At this stage, each girder acts separately as an individual simply supported curved beam, with much of its load acting at the top flange level. It is often considered that linear analysis may be used to predict the structural behaviour of composite steel and concrete I-section girders curved in plan during construction. However, when an I-section girder curved in plan is subjected to a vertical uniformly distributed load, it experiences primary bending and non-uniform torsion actions. Because of this, the vertical deflections perpendicular to the plane of the girder are coupled with the twist rotations of the cross-section. The primary bending and torsion actions, vertical deflections and twist rotations couple together to produce second-order bending actions in and out of the plane of the curved girder. The interactions between these actions can grow rapidly, and produce early nonlinear behaviour and even early yielding. Hence, the predictions of a linear theory may be very misleading for the behaviour of composite steel and concrete I-section girders curved in plan during construction. This paper uses an efficient nonlinear inelastic curved beam finite element model developed by the authors to investigate the structural behaviour of composite steel and concrete I-section girders curved in plan during construction. It is found that a nonlinear analysis is needed to predict the structural behaviour of the girders under construction loading. The load carrying capacity of the steel curved girders during construction has to be ascertained and precautions may have to be taken to prevent the failure during construction of the composite curved girders.