冷間成形円形鋼管部材の耐力と変形能の統計的評価

抄録

Cold-formed members involve uncertainties that are attributable to factors different from those common in hot-rolled structural members. These uncertainties are not incorporated in current design guides, such as an LRFD proposal. Efforts have been made by several investigators to evaluate effects of residual stresses and strain hardening due to cold-forming. These results are still insufficient to establish stress-strain models for these sections that are accurate and general enough to evaluate the load-carrying and deformation capacities of the members. This paper presents results of a probabilistic analysis based on statistical data for mechanical properties of cold-formed circular tubes. The conclusions drawn are summarized as follows : (1) Stress-strain models for circular hollow sections after cold-forming, including effects of residual stresses and strain hardening, are represented by a Ramberg-Osgood stress-strain model using compressive yield stresses and ultimate tensile strengths measured by stub-column and tensile-coupon tests. A probabilistic analysis was carried out to obtain a probabilistic density function for one remaining variable in the model. (2) Probabilistic distributions of inelastic local buckling and column buckling stresses for tubular members are derived from numerical analyses of the stress-strain models. The column buckling stress is found to be influenced by a diameter-to-thickness ratio. (3) An analysis using a simple yield line theory is found to be useful to interpret behavior of stub-columns after local buckling. (4) Prediction equations for deformation capacities of stub-columns and beam-columns are obtained. From these equations, the limiting diameter-to-thichness ratios used in the current design codes are not found to be in accord with the required ductility values.