ON ELASTIC LATERAL BUCKLING STRENGTH FORMULA FOR 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 a previous study, an elastic lateral-torsional buckling test was carried out on such members, and a simple flexural strength formula was presented for practical design. The value calculated by this fromula is safe compared with the lateral-torsional buckling test results. However, it cannot represent the influence of bolt pitch and is not accurate enough for design.The sectional shape of the member is changed in the longitudial direction, so a new torsion constatnt calculation equation is required. This paper presents a precise calculation equation for torsion and warping constants of this member and derives an elastic lateral buckling strength formula. The accuracy and efficiency of this formula are demonstrated by a comparative study using lateral-torsional buckling tests and axial buckling and twisting test results.