| The PC continuous rigid frame bridges with box-girders have been applied extensively in our country in the last 30 years. However, considerable cracks have appeared during most construction or operational course of PC bridges with box-girders,especially cracks in the webs. The appearance of cracks exerts negative impact on the safety, endurance and normal using of the structure. Therefore, it is necessary to ascertain the reason of the web cracks in box-girders not only for the preserve of the bridges but also for the designing and constructing of bridges. Combined with the West Traffic Construction Research Project, "Research on the crack reasons of the prestressed continuous and continuous rigid frame bridge being used with structure box-girders and the technology how to do with it", based on Weijiazhou Bridge (continuous rigid frame bridge with box-girders), this thesis uses ANSYS's parameterize design language(APDL), puts forward the partial and whole models of this bridge and analyzes the characteristics of the spacial force in various construction conditions. On the basis of theoretical research and the entity structural models I have made further study on the causes of cracks in the webs of the box-girders from such aspects as the change of temperature and loss of prestressed force. Through the research, I find that the concrete stress limit prescribed in the standard "Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts"(JTJ023-85) is somewhat high in our country. Although the current standard(JTG D62-2004) has amended and reduced the stress limit value,it is still unsatisfied that 1-direction is still applied to control the webs concrete crack of 2-direction stress state. On the basis of the existed test results and some concrete destroying norms,this thesis studies the stress limit value and puts forward a new concrete stress limit value, which can be viewed as a valuable reference for project design. |
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