Studies of Elasto-Plastic Behavior of Steel Braces under Cyclic Axial Force and its Fracture

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B races sometimes fracture in an early phase of a load hysteresis. It is the purpose of this study to elucidate a structural characteristic of a steel member under a cyclic axial force and its strain hysteresis until crack occurs in its local buckling section. Specimen was made of a cold formed steel tube, cold roll-formed steel spuare tube, and welded H steel. Experimental variables were slenderness ratio, width-thickness ratio, free nitrogen content, and existence of heat treatment.Main findings were as follows.1 A stain concentration occurred in a local buckling section. With the in crease of deformation amplitude, the stain amplitude in the concentrated portion increased and reached dozens of percent.2 Deformation capacity up to fracture depended on its shape of section and width-thickness ratio, and a steel square tube which has a greater width-thickness ratio reached an earlier fracture.