Analysis Of The Web Plate Crack's Origin Of Continuous Rigid Frame Bridge

With continuous progress of the level of bridge materials and construction technology, continuous rigid frame bridge structure becomes the first choice of many bridges because of its high structure quality. However, after the continuous box girder bridge's massive uses, the prevalence of box-girder web cracks becomes the outstanding obstacle to their development and has become a focus of concern in engineering academic. In order to investigate the causes of cracks in the web, this article taking Guang Yangdao bridge reality engineering project as a backing, has conducted the systemic analysis and research to the c continuous rigid frame bridge's box girder web plate's stress condition and the displacement.This article, based on analysis of the literature of China's continuous rigid frame bridge cracking, particularly in the general box girder web cracking phenomenon and the reasons for cracking, noted the deficiencies of the continuous rigid frame bridge in the design and construction. And then through space finite element method, the article has analysed the entire box girder bridge and particularly stress state of the web. In the space finite element analysis of local stress of the continuous box girder web ,the article give full consideration to various factors on the local model of the box girder and conduct the mechanical analysis of the web, especially focused on the loss of vertical prestress and Temperature gradient changes in the box girder web cracking. At the same time, the article has conduct on-site investigation of stress state of key pieces in the actual structure of the box-girder bridge web, in order to test the finite element analysis model's reliability and accuracy.In this article, the results of analysis show that the main reason why this continuous rigid frame bridge web cracks formed is: when the concrete block begins to contract, the cracking block is affected by the binding effect of the former block and the two block age difference led to the additional restriction which produce the pull stress; the differences in absorption of heat in the atmosphere of two pieces of blocks produce expanding and cracking stress on the cracking block, which is called the contraction and boundary stress and absorption heat difference stress. Contraction and boundary exist in every blocks, absorption heat difference stress only appear in rapid warming quarter in the spring. Although stress from the two combined make web cracking, only contraction and boundary stress do not have the ability to make web cracking, so absorption heat difference stress is the main factor. In addition box girder soleplate crack will have a biggish shear stress which will push the cracks to develop.