Analysis of structural behaviour in widened concrete box girder bridges

Structural performances for a widened post-tensioned concrete box girder bridge under dead load, prestressing force, shrinkage and creep of concrete and settlements of piers are analysed. The existing and new box girder bridges are connected with their flange slabs. Connection of the two bridges will cause internal force to be redistributed between them, and cause great local stress in the connecting slab. To reduce the influence of internal force redistribution, those factors such as connecting time, usage of low-shrinkage concrete and prestressing arrangement for the new bridge are discussed. The local structure of the connecting slab and factors which influence the stresses in the connecting flange slabs of box girders, are also discussed. The results of analysis show that the time for connecting the two bridges should be as delayed as possible, while the usage of low-shrinkage concrete will reduce internal force redistribution, and optimization on the prestressing design of the new bridge can improve the stress states in both the existing and new bridges. The analysis results also show that settlements of piers of the new bridge must be strictly controlled.