Study On Ultimate Bearing Capacity Of Prestressed Concrete Box Girder Mixed With Internal And External Beams

With the continuous improvement of the construction technology of the prestressed concrete box girder in the body and outside,the prestressed concrete box girder with mixed bundles in the body and outside has been more and more widely used.At present,the research of prestressed concrete box girder with mixed bundles inside and outside the body is mainly concentrated in the experiment.Its theoretical analysis is relatively less.It lacks a relatively clear understanding of the nonlinear mechanical behavior of the structure,which is not conducive to the popularization and application of the structure of mixed beam prestressed concrete box girder in the body and outside.In this paper,based on the theory of shell and shell,a three-dimensional nonlinear finite element program of reinforced concrete is written.The working state of the prestressed concrete box girder with mixed bundles in the body and outside is analyzed in detail.The development and change rules of the stress and the stress of the prestressed reinforcement with the load are obtained.The research results have certain reference value for actual projects.The main work of this article is as follows:(1)The basic theory of shell isoparametric elements is introduced in this paper.The element stiffness matrix of the degenerated shell isoparametric element is derived.Considering the nonlinear effects of concrete and steel,a three-dimensional nonlinear finite element program for reinforced concrete is compiled.Taking a prestressed concrete multi T beam bridge as an example,the analytical model of multi T beams is established.The reliability of the program is verified by experimental data.(2)According to the three-dimensional nonlinear finite element program of reinforced concrete,six typical loading conditions are designed respectively.The development of the deflection of the prestressed concrete box girder,the development of ordinary stress and the development of the stress in the body and in vitro prestressed reinforcement are discussed in detail.The failure load,failure characteristics and dangerous section deflection of box girder bridge under typical loading conditions are analyzed in detail.(3)The effect of prestressed reinforcement and prestressed reinforcement on the structural properties of the prestressed concrete box girder with the same beam distribution and the different placement of the prestressed concrete box girder is discussed.At the same time,the prestressed concrete box girder of the prestressed concrete box girder with the same bundling amount and different placement position is compared with the prestressed concrete box girder with mixed bundles inside and outside the body.The influence of the internal prestressing reinforcement and the external prestressed reinforcement on the structure performance is studied.Through the study of prestressed concrete box girder with the same reinforcement number of prestressed concrete box beams and mixed bundles inside and outside the body,it is concluded that the cracking load of the prestressed concrete box girder with reinforcement in the body is higher than that of the prestressed concrete box girder with mixed bundles inside and outside the body.But with the increase of external loads,the ultimate load of both is basically the same.(4)By changing the main influence parameters of the prestressed concrete box girder,such as the tension control stress,the number of prestressed reinforcement in the body and in vitro,and the reinforcement ratio of the longitudinal steel bar,the influence on the structure performance is discussed.It provides a scientific basis for improving the structural design of prestressed concrete box girder bridges with mixed beams in vivo and abroad.