The Ultimate Capacity Research Of Prestressed Concrete Girder Bridge Based On The Nonlinear Layer-Shell Theory

With the improvement of hoisting construction technology and standardization of design, prestressed concrete(PC) composite box-girder bridge has got widely application in small and medium span bridges as well as the span of it has increasing trend. However, the PC box-girder bridge under the standardized design is analyzed mainly based on the classical theory and the cross section of transverse distribution of strength theory at present. There are a little experiments and theoretical analysis of loading process are carried out on the PC box-girder bridge, which seriously impediment to the application and development of PC box-girder bridge. Therefor, a static loading experiment and a detailed analysis of the stress process based on the basic theory of layer-shell isoparametric elements have conducted on the background of a four-span continuous PC box-girder bridge.A space analysis method is given to the design of PC box-girder bridges and put forward the suggestions to improve the mechanical of this structure. The achievements can provide reference for the design of the PC box-girder bridge.The main research contents and conclusions are as follows:(1) The basic theory based on the layer-shell isoparametric elements has been introduced for PC box-girder bridges that have thin-walled box girder. The element stiffness matrix of layer-shell isoparametric elements has been deduced and the constitutive relation of concrete and steel material that have to consider the nonlinear mechanical behavior has been described detailedly. In addition, the estructive test of simple T-beam has been used to verity the reliability of the basic theory.(2) The static loading experiment of a four-span continuous PC box-girder bridge in operation has been applied to inspect currently operating state of it. Meanwhile, finite element model of this bridge has been annlyzed through adopting the basic theory of layer-shell isoparametric elements to contrast the results of testing and beam element modle. It turned out that this brideg has a good mechanical condition and both deflection and strain of testing is lesser than the results of FEM. Whereas this bridge which under eccentric load appears to phenomenon that the single girder undertake the major loading. It reflects that this bridge has worse lateral ties. Besides, the accuracy of layer-shell isoparametric elements exceed in the beam element when this bridge is analyzed by the finite element simulation.(3) The ultimate bearing capacity analysis of the standard design four-span PC box-girder bridge under various load arrangement has been completed. And the variation of failure load, failure characteristics and load-deflection curves of key sections have discussed in detail when this bridge unders three typical loading conditions. Study on the regularity of internal force redistribution when the compressive region concrete of this bridge has changed into plastic state. Besides, the design parameters, which include the tension control stress, the number of prestressed reinforcement, common reinforcement and stirrup, the thickness of floor, roof and web, have been studied to reflect the influence on the ultimate bearing capacity of this bridge for optimizing the structure design of PC box-girder bridges to provide scientific reference basis.(4)The change law of transverse mechanical characteristics when the PC box-girder bridge under the increasing load based on the concept of transverse load distribution factors has been researched. And the effect of mechanical property of this bridge turough add in the cross beams have been investigated. The results show that the transverse load distribution factors of PC box-girder bridges with standard design vary with the stiffness of bridge. The typical transverse theory that is used to design bridge is not agreed with the real stress state of bridge. Also, PC box-girder bridge transverse stress performance is significantly improved and the girder bear loading become more uniform after adding the across beam.