Stress concentration due to shear lag in simply supported box girders

Abstract

The shear lag has been studied for many years. Nevertheless, existing research gives a variety of stress concentration factors. Unlike the elementary beam theory, the application of load is not unique in reality. For example, a so-called concentrated load can be applied as a point load or a distributed load along the height of the web. No existing research works deal with this difference explicitly and this non-uniqueness may be a reason for the discrepancy of the stress concentration factors in the existing studies. Although many researchers employed the finite element method for studying the effect of the shear lag and it is known well that the finite element mesh must be constructed with great care to evaluate stress concentration, very few researches have taken into account the influence of the finite element mesh on the shear lag phenomenon, which may be another source for the discrepancy of the stress concentration factors. The present study investigates the stress concentration in a flange due to the shear lag in a simply supported box girder by the three-dimensional finite element method using shell elements. To be specific, extensive parametric study with respect to the geometry of a box girder is carried out. The whole girder is modeled by shell elements. The effect of the way load is applied and the dependency of finite element mesh on the shear lag are carefully treated. It is also revealed that the stress distributions both in the flange and in the web can be very different from those of the elementary theory. Based on the numerical results thus obtained, empirical formulas are proposed to compute stress concentration factors due to the shear lag.