Study On Stiffness Calculation Of Concrete Box Girder Considering Shear Lag Effect

The box girder is widely used and has been widely used in the field of modern bridge construction because of its good adaptability and many advantages.China has a vast territory and the geological situation is complex,the box section beam both to meet the safety and economic conditions but also have a greater span and thinner and lighter weight web of thin-walled box beam is born.Symmetric loads by wall structure inevitably shear lag effect is generated,causing shear deformation changes the actual cross-sectional flexural rigidity and the vertical flange plate produced may affect the safety of the bridge member.As the thin-walled box girder web area is small,the shear flow may be too large to cause the web shear damage,the current relevant design specifications in a certain range to ignore the impact of shear lag.Concrete box girder inevitably produces cracks that will affect the synergistic performance of reinforced concrete and concrete,RC box beam is more obvious for the RC box beam once the tensile zone crack section bending stiffness will be reduced.This paper focuses on the practical calculation method of bending stiffness under shear lag effect of stiffness and cracking of RC beam considering shear lag effect of box girder in considering research.(1)Based on the one-dimensional shear theory,the theoretical solution of the vertical deflection of 32 m standard concrete box girder and the elementary beam theory are studied by calculating the two-stage dead load and converted uniform load.;this paper analyzes the influence of the standard box girder under different load conditions and the vertical deformation of the beam model without considering the shear deformation.(2)From the literature to have a shear angle of the flap and it is proved shear lag shear lag effect that is relatively independent of the mechanical behavior of the viewpoint,which the material mechanics calculates the stiffness only for the pure bend section without considering the actual presence of the bending section and the effect of shear lag effect of box girder is not considered.The shear lag plate is deformed under the flange and the web of continuous shear deformation vertical deformation conditions,including the assumed vertical deflection.The paper using the standard box girder model deduces the results of finite stiffness solution of linear stiffness under shear and shear lag effect,and proves the accuracy and rationality of the method in a certain range.(3)The short-term stiffness calculation formula of the cracked reinforced concrete box girder considering the shear lag effect is deduced.Combining the analytical results of the existing box girder and using the short-term stiffness calculation method and ANSYS numerical solution,the results show that the shear lag effect of the reinforced concrete box girder calculated by the method is in good agreement with the finite element method;the RCbox girder with shear lag effect is deduced to bear the long-term modified stiffness expression under long-term load in this paper,based on the existing box girder model,the long-term deflection is calculated by using the formula given by the specification and the long-term deflection correction expression of this paper and compared with the standard calculation result,the ratio of long-term and short-term deflection of box girder is closer to the experimental results of the literature model.