Comparative Study of the Behavior and Strength of Laterally Supported Steel Beams with Laterally Unsupported Steel Beams

Abstract

A laterally supported beam is a beam that is supported along its length to prevent lateral buckling. Lateral support can be provided by bracing, sheathing, or other means to prevent the beam form deflecting laterally. This type of support is important in preventing the beam from failing under the influence of lateral loads, such as wind or seismic forces. In contrast, a laterally unrestrained beam is a beam that is not restraint(transversely) along its length which its top flange will be subjected to lateral torsional buckling. To prevent this type of buckling, both flanges of the section or at least its top flange must have lateral support. In a beam, if the flange or its compression region is sufficiently prevented from displacement and twisting, or when the compression flange is directly connected to the roof, the beam is considered braced at the same point. This paper aims to investigate the comparison of behavior and strength between fully laterally supported and laterally unsupported beams in steel structures. To carry out this study, extensive parametric analysis is performed by considering different sizes of beams, spacing of the lateral supports and comparing the strength of laterally supported beam compared with laterally unsupported beam by practical examples. The findings shows that if the steel beams have full lateral support, the plastic hinge is created at the point with the maximum moment and the strength of that beams is not limited by lateral torsional buckling. on the contrary, if the same steel beam does not have lateral support or the unbraced length of compression flange are very large, its strength is limited by lateral torsional buckling, and its strength is more than 15 % lower than if it has a continues lateral support.