Double Track Railway 2 X 90m Steel Box Girder Composite Arch Bridge Construction Process Analysis And Monitoring

The main span of Yandangshan Grand Bridge is a 2 X 90m overlaying arch bridge on the new double-track railway form Ningbo to Wenzhou. The continuous steel box girder is with a single-box and nine-cell section. The two main arch ribs are with the constant steel box section, on which there are the auxiliary steel box arches with the variable section.The bridge will be built following four construction sequences: First, assemble the steel box on the full scaffolding, and incrementally launch it to the predicted position; Second, erect the temporary trestles to assemble the main and auxiliary arch ribs, then install the hangers and conduct the first tension; Third, remove the temporary piers under the structure, and pave the deck system including its subsidiary structures; Finally, conduct the final tension for the hangers and adjust the force to the target, so that the mechanical behavior of the bridge can meet the design requirements after the works is completed. The whole construction of this bridge was finely calculated and controlled in this paper. The main contents are as follows:1.Addressed to varieties of proposed schemes about the steel box girder's incremental launching, a lot of comparative analysis and optimization were done to determine the eventual plan of the launching using the finite element method on space, which could control the Mises equivalent stress of the girder in the permitted range. The alignment and stress of the girder were monitored during the launching. The measured values and the calculated were close and the girder was put in place successfully.2.The stress and displacement of the substructures during the incremental launching were calculated and monitored. The stress of the main and the temporary pies were small and the strength met the requirement. For the longitudinal and vertical displacements at the top of the temporary pie caps, the monitored values were less than the calculated, and the stiffness met the requirement as well.3.The alignment and the stress of the bridge were calculated and monitored from the second construction sequence to the third. The closing precision of the main arches met the design requirement. The stress of the girder and the main arches were maintained at a relatively low level, and the alignment of the bridge was consistent with the calculated values.4.When the pavement of the secondary dead load was accomplished, the target forces on hangers for the final tension could be calculated in terms of the expected alignment of the bridge.And then, with the whole process of the tension simulated, the tensile forces were obtained through iterative calculation adopting the forward-analysis method. After the hangers were tensioned once employing the tensile forces, the measured forces in them were consistent with the target and the alignment of this bridge was close with the design value. This method reduced the amount of work and raised the construction efficiency. Furthermore, it can also be applied to other arch bridges and cable-stayed bridges.