Large cross-section H-shaped beams are designed to be the main beams in large span structures. The length of the beams increases, and the risk of lateral buckling become higher so that lateral braces should be set up to the beams to prevent the lateral buckling deformation (AIJ 2010). In most cases of large span structures, non-structural members such as folded roof plates are installed on the upper flanges of the beams which are effective to prevent lateral buckling and they are defined as continuous braces. However, continuous braces are not considered as lateral braces in the Japanese design code. Kimura (2013) clarified the lateral buckling behavior for H-shaped beams with continuous braces. Furthermore, in design standard for steel structures (AIJ2005), the boundary condition of beams is provided as simple supported. While, H-shaped beams are rigidly connected to the columns, which have high warping restraint against lateral buckling deformation of beams in steel moment resisting frames. Kimura (2019) shown that elastic lateral buckling load for H-shaped beams with continuous braces as the loads between simple support and warping prevention under gradient flexural moment. However, both studies are conducted by theoretical study and FEM analysis. The experimental study has not been conducted yet. On the other hand, In the FEM analysis, folded roof plates are replaced with lateral and rotational springs in the FEM model that are fixed on the upper flanges of the H-shaped beams. However, in real case the joint between H-shaped beams and folded roof plates are using tight frames and bolts. When the torsional moment of H-shaped beam by lateral buckling occurs, the joint parts and the bolt holes will be broken easily so that the rotational bracing stiffness cannot be exerted. Yoshino (2019) clarified the rotational stiffness of the folded roof plates is only about 2% of the theoretical value by torsional experiment of roof decks. In this paper, partial frame tests on lateral buckling of H-shaped beams subjected to cyclic loading are conducted to find out the effect on lateral buckling load of continuous braces and warping restraint of beam to column joints. In the experiment, eleven specimens which have different slenderness ratio, beam to column joints and bracing forms are conducted to clarified that bracing effect of folded roof plates and warping restraint effect of beam-column joints on lateral buckling of H-shaped beams. Also, the rotational stiffness of the folded roof plates is calculated to find out the deviation between the theoretical value. Finally, Elasto-plastic lateral buckling stresses of H-shaped beams with lateral and rotational bracing are evaluated using buckling curve with the modified slenderness ratio. Lateral bracing force and rotational moment of brace from these experimental results are safe to compare the Equation proposed in the reference (Kimura (2019)). © 2022 Architectural Institute of Japan. All rights reserved.
