The Research On Fatigue Performance Of PC Box-girder After Cracking

The prestressed concrete box-girder bridge has been widely used at home and abroad since it was built for the first time in the early years of last century. At the same time, the rapid development of our country’s economic promotes the progress of the transportation industry, vehicle load tends to be more heavy, the traffic transportation shows the characteristics of “large traffic volume, heavy load and channel traffic”. In many parts of the PC box-girder bridge appeared web diagonal cracks, it may be possible to shorten the service life, or directly threat to its security. To find out the influences to the performance of PC box-girder bridge after cracking under repeated loads, the article made a careful study, the main work and achievements are as follows:1、Read a lot of literature at home and abroad, the paper introduces research process of PC structure and the fatigue properties of material composition; compared the domestic and foreign relevant specification about the rules of the crack width calculation; introduced the research methods of traditional fatigue life, the fatigue crack propagation analysis method and solving process of the fatigue crack propagation life on the basis of fracture mechanics. Those provide a train of thought and theory foundations to the research of this paper.2、This paper has carried out a large contains 12 pieces of PC box girder test: three beams with static loading, three beams with two-stage variable amplitude loading, six beams with constant amplitude loading. Comprehensively analyzed the change of the load, stirrup strain development course, characteristics of inclined cracks and the related affection to the stirrup strain and crack propagation which have influence on its performance after cracking,carefully analyzed the experimental phenomena and the measured data.3、The measured data was analyzed combining with theory, deduced the calculation formula of the effective strain for the stirrup in the PC box-girder under repeated load, and put forward the diagonal crack width calculation formula of PC box-girder under repeated load;This type can calculate diagonal crack width quantitatively, the calculation accuracy can satisfy the use requirement.4、PC box-girder’s stiffness degradation model and its associated strength degradationmodel were established, studied the stiffness and strength degradation regularity of PC box-girder’s under repeated load, provide a basis for studding the actual surplus bearing capacity of the bridge, it proved that crack propagation analysis method based on fracture mechanics can be used to fatigue life prediction of PC box girder by calculation, but need further research.