In Steel Framed House (SFH), built-up member is used for stud. Usually, stud is composed by two light gauges and interconnected by self-drilling screws. In Japan, flexural buckling strength of light gauge built-up compression member is evaluated by effective slenderness ratio that is specified in the Design Standard for Steel Structure - Based on Allowable Stress Concept-. The formula specified in the Standard is based on Bleich’s assumption which was applied for heavy section. From this reason, it is questionable that the formula specified in the Standard can be directly applied in light gauge. Firstly, full scale testing were conducted to clarify this issue. Batten type light gauge built-up members were used for specimens in this study. Parameters selected to determine the configuration of the specimens were distance between connectors, separation between chords, and length of the member. Connectors and chords were connected by high-strength bolts. Length of the members were determined to have flexural elastic buckling. From the testing, Un-conservative results were observed from all specimens when the flexural buckling strength were evaluated according to the Standard. Additionally, bending moment distribution at the chord that were computed from strain gauge reading differed from Bleich’s assumption. Secondly, energy equilibrium theory was used to derive flexural elastic buckling strength of the built-up members. Bending moment distribution which were used in this derivation was based on test observation. Moreover, modified effective slenderness ratio was proposed for light gauge built-up members. The effects of distance between connectors and separation between chords were included in the formula. Proposed formula was arranged to show these two parameters clearly. Finally, supplemental results were obtained from finite element analysis (FEM) to verify the proposed formula. Length of the members used in the FEM analysis were designed to have flexural elastic buckling. From full scale testing and parametric finite element analysis, good agreements were observed from all test specimens when the flexural elastic buckling strength were evaluated according to proposed modified effective slenderness ratio. Compared to Standard, good agreements and improved results were observed from all analysis models when the flexural elastic buckling strength were evaluated according to proposed modified effective slenderness ratio.
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