Bearing Capacity Calculation Method Of Test Box Girder Based On Stress Test Of Prestressing Tendon

After the reform and opening up,China has ushered the peak of development of transportation industry,with a large number of PC bridges been constructed.However,after twenty or thirty years of operation,there are many problems,such as the transverse cracks at the bottom of the girder,the corrosion of steel bars and prestressed tendons,and so on.There are many reasons for these diseases of PC bridges,but the main reason is that the attenuation of prestress is too large,which couses the effective prestress less than expected.If the problem can not be found and solved timly,it will have a significant impact on the durability and safety of the PC bridge structures,and even couse losses to the state and society.Therefore,it is of great significance to carry out the research on effective prestress detection and safety assessment of in-service PC bridge.As an important part of transportation construction in Shanxi province science and technology project " The research of cracked and damaged PC box girder's performance ",this paper summarizes the longitudinal simulation method of effective prestress,and derives the iterative algorithm of the cross section analysis with considering the tensile strength of concrete;Secondly this paper improves the calculation accuracy of prestressing loss l1? by inproving the practical algorithm of it.This paper also presents a new method to predict the effective prestressing with multi prestressing test in cross section based on the idea of parameter identification and correction;Then the old prediction method and the new prediction method in this paper are used and compared through prestressing test and loading test of three test girders.The results show that the new prediction method of this paper involves fewer parameters and calculation steps,and is not easy to make mistakes;At last by using the prestressing predicted and iterative algorithm of the cross section analysis,this paper caculates the stress of the middle-span section of the test girders,and compare it with test value.The results show that the methods of this paper is reliable.and assesses the stiffness and bearing capacity of the three test girders finally.The results of this study can be used as reference for the safety assessment of the PC bridge based on the stressing test.