Shear-lag Effect Analysis Of Steel Box-girder Based On Hamiltonian Principle

The steel box-girder has many advantages such as strong torsional stiffness, high intensity, light deadweight, prefabricate and machining conveniently, short construction period, good integrity, small building height good integrity, succinct and beautiful appearance. With the development of the transportation, steel box-girder are widely used in bridge construction.Under the action of load, the box-girder bridge may present the phenomenon of shear lag. Overlooking this problem in designing would underestimate the stress and have serious influence on the safety of bridge. Solution methods of shear lag effect of straight concrete box-girder are mentioned in specifications of many countries now, but the researches of shear lag effect of wide flange plate steel box-girder is absent. Our country's current code for design of highway bridge and culvert prescribe the effective width of flange plate of concrete box-girder which of curved steel box-girder is not mentioned. So the research of shear-lag effects of steel box-girder is of vital significance. The meaning of'shear lag effect'was that the bending normal stress near the boundary of wing plate and web plate is bigger than the stress near the midpoint of the wing plate.When discuss the phenomenon of shear lag, the most used analytic methods are traditional classic elastic mechanics method and the calculus of variations and functional analysis based on principle of energy.But both of the two methods need to solve second order differential equation,it's troublesome.Sometimes,it needs to suppose stress function or displacement function,So the whole solutions can not be obtained.This paper, based on Hamiltonian system of elastic mechanics,simplified the simply supported beam reasonablely and researched the the issue of shear lag of the simply supportive steel-box beam theoretically under the uniform (distributed) load.Also, the parameters affecting the phenomenon of shear-lag are discussed with finite element method program.The work of this paper is as follows.First,introduced the Hamilton system of rectangular coordinate system on plain-stress problem in elasticity.The plain problem solving system is formed through variables separation and solution of transversal latent root.And the solving system can be directly used in the solution of the rectangular domain.Secondly, the solution of simply supportive box-girder under uniform (distributed) load is obtained based on st. venant principle.At the same time, the closed multinomial expression of effective width is achieved.Thirdly, the Ansys programs are used to solve one instance,made a comparison of the result of the finite element method and the result from this paper ,it demonstrate that the method in this paper is effective.Fourthly,used finite element method to modle the steel-box girder with different designparameters.And compared the effects of different size parameters on shear-lag.The result demonstrates that the effect of the width-span ratio is first, the thickness and the interval of central longitudinal partition also affect the shear-lag effect,but not as significant as the with-span ratio. The other parameters'effect can be ignored.