Behaviour of unpropped composite girders curved in plan under constructionloading

Composite steel and concrete curved bridges are often used in highways, par ticularly for motorway interchanges where high speeds require smooth change s in direction. A composite steel and concrete curved bridge often consists of horizontally curved steel girders and concrete deck slabs. The use of s teel I-section curved girders is commonplace because of their economy and e ase of construction. During construction, the curved steel girder carries a uniformly distributed load, comprising its self-weight and the wet concret e 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 st ructural behaviour of composite steel and concrete I-section girders curved in plan during construction. However, when an I-section girder curved in p lan is subjected to a vertical uniformly distributed load, it experiences p rimary bending and non-uniform torsion actions. Because of this, the vertic al deflections perpendicular to the plane of the girder are coupled with th e twist rotations of the cross-section. The primary bending and torsion act ions, vertical deflections and twist rotations couple together to produce s econd-order bending actions in and out of the plane of the curved girder. T he interactions between these actions can grow rapidly, and produce early n onlinear behaviour and even early yielding. Hence, the predictions of a lin ear theory may be very misleading for the behaviour of composite steel and concrete I-section girders curved in plan during construction. This paper u ses an efficient nonlinear inelastic curved beam finite element model devel oped by the authors to investigate the structural behaviour of composite st eel and concrete I-section girders curved in plan during construction. It i s found that a nonlinear analysis is needed to predict the structural behav iour of the girders under construction loading. The load carrying capacity of the steel curved girders during construction has to be ascertained and p recautions may have to be taken to prevent the failure during construction of the composite curved girders. (C) 2001 Elsevier Science Ltd. All rights reserved.