薄板角形鋼管短柱の高温局部座屈性能

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タイトル別名
  • LOCAL BUCKLING PERFORMANCE OF STEEL THIN SQUARE HOLLOW SECTION AT HIGH TEMPERATURE
  • ウスイタ カクガタ コウカン タンチュウ ノ コウオン キョクブザクッセイノウ

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 It is considered that cold-formed thin-walled steel structural members, which possess large width-thickness ratio, mostly exhibit local buckling behavior at both ambient and high temperatures. To verify both load bearing and deformation capacity, various experimental approaches represented by a stub column test under compressive force have been conducted and the evaluation methods on the local buckling performance have been proposed. A concept of “effective width” based on elastic buckling strength of a plate and load-distribution capacity of the buckled plate is widely used to estimate the maximum load-bearing capacity of the thin-walled steel column at structural design of the ambient temperature. On the other hand, those evaluation methods for fire resistant design in Japan have not been established, because the design method has been proposed for the heavyweight steel structures using shape steel members and thick steel plates. It is well known that stress-strain relationships at the high temperature show strong nonlinearity within a small strain range, there is, therefore, a possibility that the concept of the effective width based on the elastic local buckling strength cannot be applied for the evaluation methods at the high temperature. Main purpose of this study is to clarify the local buckling performance at high temperatures for thin-walled steel thin square hollow section members by conducting the stub column tests and propose the evaluation methods on the maximum load bearing capacity at the high temperature by using the modified effective width formula.<br> The stub column tests under a condition on constant temperature and monotonic loading were conducted. The compressive force was gradually applied for a stub column specimen after heating it by an electric furnace. The JIS SS400 steel plate (thickness: 1.6 mm) is used for the specimen. Both width-thickness ratio (B/t = 50, 65, 80) and test temperature (RT, 400, 600, 700, 800 °C) are used as experimental parameters. Loading of the compressive force at the stub column test was continued after a peak point of that was observed, because of estimating the residual strength at the post local buckling behavior. From minute investigations on the stub column test results, the following knowledge was obtained.<br> The loading peak points for all the stub column test results were observed after the local buckling behavior exhibited in the specimen, it is, therefore, considered that adapting the concept of effective width to the fire resistant design is reasonable to quantify the maximum load-bearing capacity. However, all the experimental results had the lower maximum strength than the results estimated by the past effective width evaluation formula. The modified effective width evaluation formula, which respectively substitutes the stress at 0.2 % strain and a secant stiffness at that stress for Young's modulus and the yield point, was proposed. By using this modified evaluation formula, the maximum strength at the high temperature can be satisfactorily estimated. It was, furthermore, clarified that the residual strength after the peak strength for the stub column test result approximately corresponds the estimation value obtained by the existing formula, which has been proposed by the AIJ Recommendations for Fire Resistant Design of Steel Structure (AIJ, 2017).

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