Study On Shear Lag Effect Of Steel And Concrete Composite Box Girder

Steel and concrete composite box girder is a new structure composed by concrete slab and steel box girder connected by shear connectors. Its advantages such as small cross-section size, high capacity, good dynamic performance and good seismic performance have made it widely been used. The phenomenon of uneven distribution of flange stress in box girder under symmetrical load is called the shear lag effect. Ignoring the shear lag effect may cause structural insecurity. Most of previous studies on steel and concrete composite box girder did not take the shear lag effect into consideration, so this paper will focus on analyzing the shear lag effect of steel and concrete composite box girder. The main components of the work are illustrated as follows:This paper used the minimum potential energy principle to establish the basic differential formula of steel and concrete composite box girder shear lag effect. It established deflection and stress calculation formula of shear lag effect of simply supported composite box beam and cantilever composite box beam under the concentrated load and uniformly distributed load.This paper established the calculation formula of equivalent flange thickness and stiffeners area of steel and concrete composite box girder by using the bar simulation method and the transformed section moment of inertia. It established the differential formula of bar simulation method, and gave the calculation formula of the simply supported composite box beam under the concentrated load and uniformly distributed load by using the three-bar simulation method.This paper analyzed the influence factors of steel and concrete composite box girder, including loads, span-width ratio, web inclination. The results showed that the span-width ratio is the most important factor to affect the shear lag effect of composite box girder.This paper established the finite element model to simulate the simply supported beam under the concentrated load and uniformly distributed load by using ABAQUS, the finite element analysis program software. The results reflected the shear lag effect of composite box girder.Empirical calculation formula of the concrete flange effective width in mid-span section of simply supported steel and concrete composite box girder was presented by using the regression fit.