This study assessed the inelastic lateral-torsional buckling behavior of steel I-beams under elevated temperatures. Numerical simulations were conducted using the finite element program ABAQUS. The beam models were subjected to uniform bending and varying temperature loads from a normal temperature of 20 °C to an elevated temperature of 600 °C. These thermal loads were applied at the compression flange, tension flange, half of the beam, and throughout the entire beam. The combined effects of residual stress and geometric imperfection on the inelastic buckling strengths of the beams were also considered. The results showed that the scenario in which the entire beam was heated demonstrated the highest strength degradation. In addition, the compression flange of the beam was observed to be critical; thus, the local buckling of the compression flange greatly contributed to the decrease in the buckling strength compared with the other cases.

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This paper presents a nonlinear numerical study on the moment resistance of composite steel-concrete beam using fire insulation subjected to various fire scenarios and basic loading conditions. The temperature-dependent material properties of fire insulation, concrete and steel were taken into consideration. The nonlinear finite element analysis was done by utilizing a commercial finite element program, ABAQUS. The obtained moment capacity of the composite I-beam from the current fire code was also performed and compared. The results showed that the fire scenarios and the fire insulation thickness have a great influence on the temperature distribution and strength degradation of the composite beam. The capacity of the beam in hydrocarbon fires, which is the most severe scenario, decreases faster than that in ISO834 standard fire and external fire. The fire resistance of the beam increases as the fire insulation thickness increases due to the temperature degradation in the steel beam. The calculated results from the current fire codes give conservative value at normal temperature and low temperature. The current fire codes can give unconservative values at high temperature when there is a great temperature discrepancy between parts of the beam. A new factor was proposed to determine the fire moment resistance of the composite beam with non-uniform temperature.

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This study presents a numerical investigation of the elastic critical lateral-torsional buckling of a steel beam subjected to simultaneous transverse loading at the top flange and negative end moments. Here, the elastic critical buckling of the steel beam was estimated by utilizing the finite element software ABAQUS. In addition, the influence of the length-to-height ratio was taken into account. Additionally, the predicted values for elastic critical buckling when applying existing design codes and a previous study were also analyzed and compared to the numerical results of the finite element analysis. The result of the comparison revealed that the projected values from the design codes and the study are conservative for the majority of cases and have a tendency to be too conservative when the length-to-height ratio increases. Furthermore, a new equation with a factor considering the influence of the length-to-height ratio and transverse loading on the top flange is proposed, and the proposed equation shows sufficient accuracy and less conservative values for most cases.

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