Analysis Of Cracks In Prestressed Concrete Continuous Box Girder Bridges

Aiming at the crack phenomena in long-span prestressed concrete continuous box girder bridges at present, on the background of Modaomen Bridge in Guangdong province, the main factors effectting the capability against cracking for long-span PC box girder bridges are studied and discussed in this thesis. The main contents are described as follows:(1) Through looking over lots of literatures, the standpoint is brought forward in this thesis that the key on analysis of the capability against cracking for long-span PC box girder bridges is three-dimensional stress. It is necessary to study on the analysis of the capability against cracking based on three-dimensional stress, especially on the local analysis.(2) In the three-dimensional finite analysis of the whole model, the stress response of the structure under the permanent load (dead load + prestressing force) add each single factor (shrinkage, creep, temperature difference, foundation displacement and live load) is analysed, and the shortage of the plane software is pointed out, the conclusion is made that prestressed reinforcement is the most important factor and local temperature difference takes the second place.(3) Aiming at the deficiency of capability against cracking in bottom deck of span center in midspan, the local analysis is applied. And the conclusion is considered to be that overlarge prestressing reinforcement in bottom deck is the main factor resulting in the ultralimit of principal tensile stress .The optimization case is proposed.According to the calculation and analysis in the whole thesis, it is necessary to analyse the capability against cracking based on three-dimensional stress. And through the local analysis , the more reasonable design precepts of the prestressing force , line shape and reinforcing steel against break-up in the bottom deck of long-span PC box girder bridges can be obtained, then the crack development of the bottom deck can be avoided.