Study On The Origin Of Cracking Of Long-span Pc Continuous Rigid Frame Bridge

Since the first long-span PC continuous rigid frame bridge was built in1988in China, nowadays more and more PC continuous rigid frame bridges are under construction or have been built, and the spanning capacity of these bridges is growing fast. However, according to the actual situation of some domestic and foreign engineering projects, girder cracking occurs in a large number of continuous rigid frame bridges during the construction or operation process, which has become the common problem of long-span cantilever constructed box girder bridges. Therefore, research on the crack origin of the continuous rigid frame box girder bridge is of great importance.In this thesis, Xiluodu Jinsha River Bridge was taken as the example project, the influence of spatial stress state and crack resistance under temperature effect and prestressing effect were analyzed respectively. The main factors leading to the bridge cracking were discussed combining with the actual test results. The main research work was carried as follows:1. The basic forms and origins of cracks of PC continuous rigid frame bridge and the main factors which cause box girder cracking were summarized and analyzed.2. The analysis theory and bridge design criteria at home and abroad of temperature effect was introduced briefly, the longitudinal stress distribution under different temperature gradient mode and the spatial stress state considering vertical temperature gradient and internal-external temperature difference the box girder was analyzed.3. The stress distribution in the deck slab, web and bottom flange of the box girder under different value of prestressing loss was calculated, the contribution of different kind of prestressing on the crack resistance to different parts of the box girder was discussed.4. The shear lag effect caused by prestress in cantilever construction stage was calculated, the spatial distribution of box girder longitudinal normal stress by prestressing was studied.5. The spatial stress state of the top plate of the example project under each single load was calculated, the main cause of the cracking was analyzed.