Research On The Web's Work Of The Long-span Prestressed Concrete Box Girder Bridge

The prestressed concrete (PC) box girder bridges have been widely applied due to their advantages in applicability, safety and economy and so on. However, numerous investigations indicate that the representative cracks, especially skew cracks develop in the bridge web. The skew cracks have effect on the appearance, bearing capacity, service life of the bridge and even the traffic safety. The causes of skew cracks in web are multiple. This thesis investigated the effect of the stress loss of vertical prestress on the development of skew cracks and proposed the important issues in the design and construction of PC bridges.(1) Based on the experiments, this thesis discusses the stress loss of vertical prestress caused by deformation of anchorage, the resilience of the tendon and the joint compression (σl2), the elastic compression of the concrete (σl4) and the relaxation of the tendon (σl5). It is concluded that the anchorage deformation is dominated in vertical stress loss. Measures are suggested to diminish the loss of the vertical prestress during the design and construction of the bridge.(2) To clarify the distribution of the vertical stress of the web under the action of the vertical tendon, a three-dimension (3-D) finite element (FE) model is established to calculate the stress distribution of the web under the action of one bind and binds of vertical tendons and investigated the analytical method on vertical stress, the dispersion angle of stress and the calculation of the suitable spacing between the tendons.(3) According to the calculation result of 2-D FE model, a 3-D FE model was established for the Jintang Xiangjiang Bridge to analyse the effects of the tendons in the top deck, the base plate and the web on the web. The tendons in the top and the base plate have an effect, namely"opposite tension", on the web. Moreover, it is found that the web prestressed reinforcement is necessary since it is capable of lowering the principal tensile stress. The reinforcement arrangement without the web prestressed reinforcement is not mature in theory since its disadvantages are not solved in practice. This thesis brings forward some advices on how to improve the performance of web prestressed reinforcement based on the calculation...