Study On The Coupling Effect Of Creep And Shear Lag Effect Of Concrete Box Girder

Concrete box girder has the characters of light weight, large stiffness of bending and torsion and its good performance on force is widely used in bridge engineering structure.Creep of concrete often causes the redistribution of the section stress, but also due to the shear lag effect of box girder, the distribution of the stress redistribution caused by creep will also be affected by the shear lag effect. Therefore, how to consider the effect of creep on the shear lag effect and establish the corresponding theoretical analysis method is very necessary.In this paper, the coupling effect of creep and shear lag effect on concrete box girder is studied through theoretical research and numerical simulation. The main research content is as follows.Considering the difference of sizes and ages of the top,web and bottom plate exist the different initial creeps and ages in the concrete box girder with single box and single chamber,the calculation formula of the creep self-restraining stress was deduced using the theory of aging and plane-section assumption. And using the energy variational method, the shear lag control differential equation considering the creep self-restraining stress is also established.The results showed that the proposed method can effectively calculation of the creep self-restraining stress, and it has the ability to constrain the development of the cross section stress, which reduce the hear lag effect. The analytical solution in this paper in line with the expectations.The influence of the creep self restrained stress on the deflection of beam and the section stress generated in the concrete box girder considering the differences of the loading age, the total creep development time and the difference of the age between the top, web and the bottom plate. The results show that the deflection of a simply supported beam grows with the increasing of the age difference and the creep time, and decreases with the increasing of the loading age. The section stress increases with the increasing of stress loading age and creep time, and decreases with the increasing of age difference.For the statically indeterminate structure existing the structure system transformation, the calculation formula of the creep secondary internal force stress was deduced considering the difference loading ages between the beam segments. The influence of the creep secondary internal force stress on the deflection of beam and the section stress generated in the concrete box girder considering the differences of the loading age and the total creep development time.The results show that creep secondary internal force stress causes the stress redistribution, and the shear lag effect in the negative bending moment region is obviously decreased, while in the positive bending moment region is opposite.Using the secondary development tool to modify the user’s creep subroutine usercr.f provided by the ANSYS according to the "Code of Design for Reinforced and PrestressedConcrete Highway Bridges". So it can simulate the creep of concrete. The finite element model is established using the Solid45 element to simulate the influence of creep on the shear lag effect under the action of dead load in the concrete box girder with single box and single chamber and the continuous beam which exists the structure system transformation. The results show that the method proposed in this paper is feasible and has a high accuracy comparing with the ANSYS numerical solution.