Study On Shear Properties Of Reionforced Thin-wall Box Girders Under Vertical Prestressed

For its good mechanical properties and stability of space, the box beam, in modern bridge design, has become a first choice for many bridge designers. Although the concrete box girders are very popular, the design theory is not perfect, the Shear design of concrete box beams is one of the elements need to be improved. As the shear performance of box girders is affected by many factors, it requires a lot of tests and theoretical analysis. Based on these, the paper which takes the vertical prestressing as a factor, presents the researches on the shear capacity of vertical prestressed concrete box girder. And the main research work is summarized as follows:(1) Both the domestic and foreign research and development of shear strength of concrete box girder and the status and development of the truss theory are reviewed, then combining some researches of shear performance of the box girder, the main contents of this paper are presented.(2) Taking Red River Bridge in Laibin Guangxi as the prototype, finite element method is used to analyze its principal compressive stress level of webs under vertical prestressed, then taking it as the design standard, the test beams are designed.(3) Based on shear tests of the vertical prestressed thin-walled box girders, the main mechanics of test beams with different parameters such as fracture behaviors and failure modes and the beam deflection, concrete-principal tensile strain, the average web strain, hoop strain, web reinforcement strain are analyzed. Then the shear capacity of the test is calculated with several different typical norms at home and abroad, and it is compared with experimental data, results show that the norms present a safe capacity calculation for reinforced concrete box girder except Railway Bridge design specification and of Soviet Union code.(4) A softened truss program is developed to predict the shear capacity of the box girder and it is verified by experimental results. It is proved that the truss program can simulate the beam shear test performance very well. On this basis, using validated non-linear process, the parametric analysis is carried out to study the box girder shear properties with the different parameters, which select the vertical prestressed strength and spacing of vertical tendon as factors.