Study On The Effect Of Diaphragm On The Distortion Of Steel Slab Box Girder

With the wide use, the effect of distortion on the mechanical properties of steel slab box girder is more and more drawn attention by engineers. In engineering practice, the way of install diaphragms is regard as the most effective method to reduce distortion effects. But the research about diaphragm, such as the rational density and position of diaphragm installation, the difference of distortion effect under different boundary conditions and load cases, is very deficient. So it is significative to investigate the influence rule of diaphragm to distortion to project practice.In this paper, the effect of diaphragm density on restraining the distortion of thin-walled steel box girder with rectangle cross section is analyzed based on the finite element method. With different load cases of concentrated load and uniformly distributed load and different boundary conditions of two simply supported ends, two fixed ends and cantilever, the displacement and stress are examined individually and compared with each other under distortion, torsion, bending, and eccentric loads cases. By changing the amount of the diaphragm, the relations between density of diaphragm and distortion effect are investigated. According to the results, variation curves of distortion effect with density of diaphragm under different boundary conditions and load cases are drawn. Based on the analysis results, a simplified design calculation method of steel box girder subjected to eccentric load is proposed. Analysis results indicate that:â‘  Installing amount of diaphragms can effectively reduce the distortion effects.There is a close relation between distortion and density of diaphragms, the density of diaphragm is determined by distortion effects.â‘¡ Even with a fairly great density of diaphragms, the distortion effects can not be neglected compared with the effects of rigid torsion.â‘¢ The effect of diaphragm on distortion are different under different load cases and boundary conditions.â‘£ In the places of diaphragm installation, the deformation is negligible. For box girder subjected to dead force, only one diaphragm at load point can reduce the deformation to a negligible level.