Steel column testing in which a compressive axial force and a cyclic biaxial bending moment were applied simultaneously was conducted in order to clarify the structural performance of the column. Although the AIJ beam‐column design formula provided overly conservative results, the correlation equation for full plasticity evaluated the results with reasonable accuracy. The loading direction was not crucial to the plastic deformation capacity. As a result, the limitation applied to columns in order to guarantee sufficient plastic deformation under a loading direction of 0‐degree can also be used for columns with a loading direction of 45‐degree.

PurposeIn this study, the effects of strain rate on the bending strength of full-scale wide-flange steel beams have been examined at elevated temperatures. Both full-scale loaded heating tests under steady-state conditions and in-plane numerical analysis using a beam element have been employed.Design/methodology/approachThe load–deformation relationships in 385 N/mm2-class steel beam specimens was examined using steady-state tests at two loading rate values (0.05 and 1.00 kN/s) and at two constant member temperatures (600 and 700 °C). Furthermore, the stress–strain relationships considering the strain rate effects were proposed based on tensile coupon test results under various strain rate values. The in-plane elastoplastic numerical analysis was conducted considering the strain rate effect.FindingsThe experimental test results of the full-scale steel beam specimens confirmed that the bending strength increased with increase in strain rate. In addition, the analytical results agreed relatively well with the test results, and both strain and strain rate behaviours of a heated steel member, which were difficult to evaluate from the test results, could be quantified numerically.Originality/valueThe novelty of this study is the quantification of the strain rate effect on the bending strength of steel beams at elevated temperatures. The results clarify that the load–deformation relationship of steel beams could be evaluated by using in-plane analysis using the tensile coupon test results. The numerical simulation method can increase the accuracy of evaluation of the actual behaviour of steel members in case of fire.

The design formulae of beam‐column are provided by Recommendation for Limit State Design of Steel Structures (LSD) in Japan. The design recommendation shown in LSD is derived from the test results that are basically obtained from one end monotonic bending moment. Therefore, it is necessary to examine whether these formulae can appropriately evaluate the strength of the beam‐column under cyclic loading condition. In this paper, the test results of the deep‐column are reported. The dimensions of the specimens were determined per LSD. Deep wide‐flange section H‐150×75×5×7 (unit: mm) is used for the specimen. From the testing, a few unconservative results were observed in LSD design formulae.

Steel column testing in which a compressive axial force and a biaxial bending moment were applied simultaneously was conducted in order to clarify the structural performance of the column. Although the AIJ beam-column design formula provided overly conservative results, the correlation equation for full plasticity evaluated the results with reasonable accuracy. The loading direction was not crucial to the plastic deformation capacity. As for columns with a loading direction of 45 degrees.

PurposeThis work examines the effects of strain rate on the effective yield strength of high-strength steel at elevated temperatures, through tensile coupon tests at various strain rates, to propose appropriate reduction factors considering the strain rate effect.Design/methodology/approachThe stress–strain relationships of 385 N/mm2, 440 N/mm2 and 630 N/mm2-class steel plates at elevated temperatures are examined at three strain rate values (0.3%/min, 3.0%/min and 7.5%/min), and the reduction factors for the effective yield strength at elevated temperatures are evaluated from the results. A differential evolution-based optimization is used to produce the reduction-factor curves.FindingsThe strain rate effect enhances with an increase in the standard design value of the yield point. The effective yield strength and standard design value of the yield point exhibit high linearity between 600 and 700 °C. In addition to effectively evaluating the test results, the proposed reduction-factor curves can also help determine the ultimate strength of a steel member at collapse.Originality/valueThe novelty of this study is the quantitative evaluation of the relationship between the standard design value of yield point at ambient temperature and the strain-rate effect at elevated temperatures. It has been observed that the effect of the strain rate at elevated temperatures increases with the increase in the standard design value of the yield point for various steel strength grades.