Experimental Studies on the Fracture of Tension Bracing

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Braces sometimes fracture in an early phase of a load hysteresis. It is the purpose of this study to elucidate the mechanism how they fracture.In the first year, we conducted alternating axial loading tests to angle braces. As a result of these tests, the fracture occurred in the longitudinal position of there local buckling. It was guessed that at this point, the shape of section totally changed from the original shape, and when they were put tensile force, only limited part of the section resisted the fracture. A phenomenon of this fracture is essentially the same as bending members post-buckling fracture.Then, in the next year, we conducted alternating bending tests which was easy to laod and measure of strains, by means of such test pieces as some square-shape steel tubes. As a result of the measurements of strains at the longitudinal position of local buckling occurred, it was guessed that at the point of the fracture, the fluctuation of the longitudinal strains was extremely high tensile stress and compression stress occurred repeatedly. Then we tried to calculate the stress by means of an accomplished mathematical models of stress-straln curve, we found that we could not express precisely the parts close to the fracture by these models.In the final year, we conducted alternating bending tests with some square-shape steel tubes. We conducted alternating tensile-compression tests of the material which controled by the strain hysteresis measured at the point of fracture, so as to know the stress hysteresis at the point. After calculating the absorbed energy from the stress-strain curve, we found that the energy had reached to the material's limit.In conclusion of these tests, post-buckling fracture caused by reduction of effective sectional area and plastic fatigue.