Research On Displacement And Combination Method Of Displacement Action Effects For Long-Span Cable Supported Bridges

As the stiffness of long-span cable supported bridges is low, the displacement of the girder always large under load and natural function. Beam-ends displacement is a important design parameters for construction and devices of girder end, and for the bridge health monitoring. So, study on the effect action, construction factor, and the combination for action effects of beam-ends displacement that has great engineering values and important meaning. In the paper, it take cable-stayed bridge and suspension bridge as object of study, action and structure factor that effect beam-ends displacement was analyzed using FEM method, and the combined effect of girder displacement has studied based on the reliability theory. In turn, design method of displacement parameters for devices of girder end was put forward. The main conclusions are as follows:1. Systematically study the influencing factor such as temperature, vehicle, static wind and earthquake which how to influence beam-ends displacements. For different cable surpported bridge, displacements and rotation angles which need calculation in bridge design was definited. which action is must be take into account when calculating beam-ends displacements was also provided. The results of studied on rotation angle show that the current limit rotation angle(±0.02rad) can not meet the needs of all of cable surpported bridges, it must be specific design.2. The structure factor, such as auxiliary pier, supports frictional resistance, connections between tower and beam, which how to infuence on displacements and rotation angles was studied Systematically, and which structure factor is must be take into account when calculating beam-ends displacements of cable supported bridges was definited. Rigid-plastic model was used to analyze the effection of supports frictional resistance on beam-ends displacement and results indicated that the supports frictional resistance should be include During the cable-stayed bridge displacement prediction. Flexible cable between tower and beam can efficiently decrease the beam-ends longitudinal displacement caused by vehicle, static wind and temperature longitudinal gradient of tower. but it may be enlarge the beam-ends longitudinal displacements under the excitations of earthquake with designated frequency spectrum.3. Based on First-order Second-moment Method on reliability analysis, set up the action effects combination method of beam-ends displacement effects, direct towards the influence factors of beam-ends displacement. Defined the design reference period and target reliability index of girder fixtures according to the characteristic of them, derive the maximum distribution during reference period using the probability distribution function of loads, certain the partial safety factor of action effects combination. The advantages of the combination method are that it is banausic and convenient, and has clear reliability index.4. According to the influence factors of girder displacement and the action effects combination, taking all displacements and rotations of girder end, improving the design methods for displacement parameters of beam-ends devices and construction.