Effect of truss installation sequence on deviation during launching of a box–truss girder

Steel box–truss composite girders (BTCGs) are generally used on cable-stayed railway bridges – the steel box with a truss on top together provide the stiffness and resistance to the applied bending moments and axial forces of the girder. When subjected to strict construction period requirements, the box and truss should be constructed at the same time to shorten the construction period. In order to avoid excessive initial installation stresses caused by auxiliary measures, adjusting the upper chord members of the truss installation sequence was investigated. The results of finite-element analysis and a practical application proved the validity of the method. The assembly error of the upper chords can be reduced to within 3 mm, meeting the requirements of field assembly. At the same time, the method can effectively reduce the free-end deflection of the launching nose during the sequential launching construction of the BTCG. The method shortened the construction period of Yuxi River Bridge by 5–6 months.