The Double Track Railway 90m Composite Arch Bridge Steel Box Girder Program

Yandangshan Bridge is a 2×90m span stacked arch bridge with two railway lines, which skewed strides over Ningbo-Taizhou-Wenzhou highway with an angle about 22°. Its steel box girder is firstly assembled on a model frame and then incrementally launched to position because of the heavy traffic and clearance limitation. The steel box girder of the bridge is heavy and long, which makes the incremental launching very difficult and the mechanical behavior of the box girder during launching very complicated. Several launching methods were analyzed and compared. Some key problems such as mechanical state and local stability were systematically studied. The main work which has been done is as follows:1. Finite element analysis method to simulate incremental launching was studied. Analytical method was proposed by combining the overall analysis with local analysis. Simulating methods of the the precamber of the girder and the deformations of the launch bearing and the bent caps were discussed.2. Method 1, namely the launching method with four temporary piers was analyzed. The results showed that: with the length of cantilever increasing, the contact area between the launch shoes of the front pier and the steel box girder decreased. In the longest cantilever state the local stress of steel box girder was extremely high in ideal case of ignoring the precamber and the bent cap deformations.3. Based on method 1, the method was put forward in which a tower crane was used at the front pier to apply a vertical force to the girder end. The results showed that: in ideal case, the tower crane must be used when the length of cantilever was over 22 meters in order to satisfy the strength requirement of the girder. The relationship between the length of cantilever and the necessary vertical force was given. The disadvantage of this method was that the tower crane must be moved for many times during the incremental launching.4. Based on method 1, the method was put forward in which a tower with stayed cables was used at the steel girder. The results showed that: when prestress had not applied to the steel girder by stayed cables, the mechanical state of the steel box girder was not improved. However, the strength requirement was not still satisfied with 60 percent of prestress of stayed cables.5. The method in which six temporary piers were set between the three main piers during launching was analyzed. The strength of the steel box girder was not satisfied when the precamber and the bent cap deformations were considered in analysis. Based on analysis and comparison an improved measure was suggested to improve the deformation of the bent caps by increasing different heights of the launching shoes. The mechanical behaviors of the steel box girder by this measure were studied. The results showed that: with the improved measure adopting, this method was feasible. The strength and the stability of the steel box girder were satisfied.The research results of this paper can provide the ideal for the selection of optimal incremental launching construction method of Yandangshan Bridge and references for other bridges which will apply incremental launching construction.