Study On The Relation Between Cracks And Stiffness And Load-carrying Capacity Of The Prestressed Concrete Box Girder

With the rapid development of our nation's traffic utilities, techniques relevant to prestressing have been continuously improved and prestressed concrete box girder bridges are common in China. However, concrete cracks occur on many of the box girder bridges in service. The cracks impair the safety and durability of the bridges, which must be duly reinforced and repaired. Before the decision-making, a scientific estimation must be made about the load-carrying capacity of these prestressed concrete box girder bridges so as to determine the maintenance plan. Currently, research on cracking prestressed concrete box girder bridges remains insufficient, hence precise estimation about the real state of these structures is hard to make.Combined with the Western Project about Communication Science and Technology entitled "Research on the Cause and Disposal Technology of the Cracks Occurring on the P.C. Continuous Box Girder and P.C. Continuous Rigid Frame", this paper starts from the chief stressed cracks (cross cracks and diagonal cracks) and makes a systematic study of the load-carrying capacity of cracking prestressed concrete box girder bridges.This paper, according to a statistical viewpoint, sets up statistical parameters for cross cracks and diagonal cracks and turns the factual cracks into average cracks in a statistical sense whereby cracks can be described quantitatively. It also provides the basis for simulating cracks by means of FEM. This paper also puts forward the Section Analysis Method for cross cracks, the Plane Frame Model for diagonal cracks and the Discount Coefficients for the stiffness and load-carrying capacity of damaged bridges.Sensitivity analyses of crack parameters for prestressed concrete simply supported beam bridge and prestressed concrete continuous beam bridge are made respectively. The analysis data demonstrates that the cross crack width is the most sensitive parameter, the diagonal crack number is a sensitive parameter, and the diagonal crack height is not a sensitive parameter. So, we can seize primary influence factor, predigest or ignore secondary influence factor, and furthermore take an effective numerical simulation for the structure with cracks.In the laboratory, model beam experiments are done. Compare the experiment result with theoretical result, we can conclude that the theory raised in this paper is reasonable and the result is credible. This paper provides references for estimating the load-carrying capability of damaged bridges, and has important engineering application worth.