Buckling Of Stiffened Plate Under Uniform Compression With Stiffener Torsion Included

Owing to the excellent post-buckling performance, closed-section stiffeners are recommended in the high-rise steel structure design code. Unlike open-section stiffeners, the closed-section ones have large torsion rigidity. But present design codes for minimum stiffeners calculation are all for open-section members and based on the assumption that the torsion rigidity of stiffeners is small and can be neglected. Eccentrically stiffened plates are more economically and mechanically efficient than concentrically ones but the analysis of the problems is very complex. So some relatively conservative methods are adopted in present codes. The behavior of stiffened plate under uniform compression with torsion rigidity included was studied and emphasis was put on the effect of torsion rigidity on minimum stiffeners. And a convenient and accurate method to determine the effective stiffness of eccentrically stiffeners was studied.Firstly, the buckling behavior of stiffened plate under compression with stiffener torsion included was studied using principle of minimum potential energy and the POWELL algorithm was used to obtain the buckling load and the associated mode. An example demonstrated the stiffening mechanism of longitudinal and transverse stiffeners, that is, longitudinal stiffeners are dependent bracing system and transverse ones are independent. Another example shows that determining the minimum stiffener based on the neglection of stiffener torision would be unsafe.Secondly, the governing equations for the buckling of stiffened plate under uniform compression were derived. And an accurate equation to describe the relationship between stiffener area and stiffener threshold stiffness was obtained based on the governing equations. Moreover, the drawback of the method was also pointed out and a FEM model which was the same as the analytical model was established to analyze the effect of the stiffener torsion and the unloaded boundary condition on the stiffener threshold. In the end. an equation with physical significance to determine the stiffener threshold was suggested and verified.Thirdly, a method to determine the effective stiffness of eccentric stiffener is brought up based on the principle of stiffness superposition and the distribution of stress of stiffener during buckling. With the method, the problem of eccentric stiffener can be transformed to an concentric one. And the factors that affect the effective stiffness of eccentric stiffener were analyzed.Finally, three typical problems of the beam-rail system under wheel pressure were studied using ANSYS and analytical method. The stress distribution and maximum compressive stress at the top of the crane beam web in both continuous and discontinuous rail cases were analyzed numerically. A formula for the maximum bearing stress amplification factor at the top edge of web due to the track discontinuity was brought up. The contribution of rail flexural rigidity to the elastic stability of the web under wheel pressure was studied. It showed that the flexural rigidity of rail could not improve the stability of the web further if the stress dispersion due to the presence of rail has been included. And the stability analysis of web plate under wheel load was conducted, in which the bending moment due to the wheel load were fully eliminated by exerting counterbalancing shear stresses on the top and bottom edges. And a formula with good accuracy was proposed for elastic buckling coefficient of web under wheel pressure.