Effects Of The Diaphragm On Mechanical Behavior Of The Simply Supported Fabricated Reinforced Concrete T-girder Bridge

In the simply supported fabricated reinforced concrete T-girder bridges, the diaphragm set condition and damage condition have a great effect on the mechanical behavior and the reliability of structures during the design stage and operation stage. Therefore, based on the concept of lateral load distribution, the lateral load distribution performance and reliability of structures under different diaphragm set conditions and damage conditions are comprehensive studied. The main research works and results are as follows:(1)During the design stage, when the vehicular load condition is the same with that of General Code for Design of Highway Bridges and Culverts, the intermediate diaphragm has a detrimental effect on the structure. The diaphragm reduces the force in the internal girders, but increase the force in the external girders, and the design force in all girders increases. Because the load condition of the Code is the worst load condition, so the intermediate diaphragm is bad for the structures.(2)The “single plate bearing” phenomena is explained from the angles of the shear force in the flange and the torque moment in the girder. Most engineers think that the “single plate bearing” phenomena is resulted by the increasing bending moment and shear force in the girders after the diaphragms are damaged, especially the intermediate diaphragm. This study suggests that the intermediate diaphragm cannot reduce the bending moment and shear force in the girders, but can reduce the shear force in the flange and the torque moment in the girder, which is favorable for the vulnerable points of the structures.(3)The practical calculation chart is given for the common section forms in the fabricated reinforcement concrete T-girder bridges. Based on the rigid-connected slab(beam) method, this paper computes the lateral load distribution factors under the load condition of the Code and makes the calculation charts for bridge design use.(4)The reliability of structure is studied under the actual vehicle loads for different intermediate diaphragm set condition and damage condition. The actual vehicle loads are different from that of the Code, and this paper use the actual vehicle loads of 62 consecutive days on a highway to get the structure reliability. The research suggests that the intermediate diaphragm can improve the structure reliability under the worst load condition, so it is better to maintain the diaphragm without delay if it is damaged.