EXPERIMENTAL STUDY ON LATERAL BUCKLING BEHAVIOR OF WELD-FREE BUILT-UP MEMBER MADE OF H-SA700A HIGH-STRENGTH STEEL

Abstract

Researchers, including the authors of this paper, are striving to develop main members of built-up structures using 780N/mm2 high-strength steel for a new built-up structural system that prevents buildings from collapsing or being damaged by a severe earthquake (JMA seismic intensity 6.5) and enables rapid functional recovery. The authors propose a weld-free built-up structural member that has a cross section of two channel steel members made of high-strength steel stitched together with bolts. This member has high strength, so that its cross section can be small and it becomes slender, thus creating the possibility of buckling problems.In this study, lateral-torsional buckling tests were conducted on beams with various stitching bolt pitch under uniform bending moment and bending moment gradient along the member axis. Then, a calculation formula for the flexural strength was presented. The values of the flexural strength obtained from calculation were compared with those obtained from the lateral-torsional buckling tests. As the long distance between the supporting points was required for the elastic lateral-torsional buckling tests, a new loading apparatus was fabricated. Precision, supporting conditions, and loading conditions of the apparatus were verified before the experiments. These results show that:1) Although a twist angle appeared from an early stage, the initial stiffness remained substantially unchanged in the relationship between the bending moment M and the support point twist angle.2) When the bolt pitch was increased, the lateral buckling strength was reduced. The effect produced by the stitching bolt pitch on the lateral buckling strength was relatively large.3) If the bolt pitch remained within the range from 200mm to 800mm, the calculated values of lateral buckling were almost same as the experimental values for both cases of uniform bending moment and linearly changing bending moment.