CONTRIBUTION OF LONGITUDINAL STIFFENER TO THE STRENGTH AND STIFFNESS OF COLD FORMED STEEL BEAM C-SECTION

Abstract

The shear center of cold formed steel beam C-section is not at the same point as that of its centre of gravity. Therefore, applying bending load on this section will technically produce torque along them. In order to reduce the excessive deformation as well as to reduce the normal stress due to the warping moments produced, the installation of stiffeners in the form of steel plates in longitudinal direction at a certain distance is proposed. In order to study the above structural behavior, this research is involving two stages, including analytical and experimental of the bending beam element model with warping torsion. During the analytical stage, longitudinal stiffeners are modeled as an unbraced fixed torque, where the derivative of the rotation angle is restrained, and the rotational is released. This element model is also compared with the beam model as a mesh of flat shells. While during the experimental stage, the influence of longitudinal stiffeners is investigated by placing the stiffeners at varying distances and dimensions. Additionally, unsymmetrical bending load with utmost half of normal stress due to combined bending and warping torsion, close to the allowable stress, is applied. The result shows that, generally, the installation of longitudinal stiffeners, either placed evenly along the beam or at the ends only, will increase the strength and stiffness of the beam. Moreover, longitudinal stiffeners installed evenly contribute strength and stiffness more than that is placed on the ends, if the same weight of stiffeners is installed. Meanwhile, the comparison of analytical results with the model of bending and warping torsion elements of the experimental results shows good accuracy. The accuracy of beam model as a mesh of flat shell is better and more conservative compared to the experimental results. Finally, the contribution of this research is that only by installing two longitudinal stiffener plates on the both ends, with a weight of 3.9% of weight of the beam, both the strength and the stiffness are increased up to 35.9% and 38.3% respectively. This is very useful to solve the case where many purlins deformed excessively due to unsymmetrical bending loads.