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• Experiments on FTB of steel arches at elevated temperature are conducted. • The technique of importing nonuniform temperature field into the FEM of structural analysis is proposed. • The influence of the load ratio and geometrical imperfections on the critical temperature of FTB is analyzed. • Thermal expansion plays a dominant role on the FTB behavior of arches. This article reports the fire resistance experiments conducted on I-section circular steel arches, as well as the observed out-of-plane flexural–torsional buckling (FTB) behavior and in-depth finite element numerical simulation results. The test was carried out using a large fire test furnace to provide a real fire environment with a nonuniform temperature field. A specially designed loading device allowed for unconstrained out-of-plane deformation of the specimens inside the furnace, thereby achieving effective load conditions and noncoupled response of the components. Numerical analyses were performed using a combination of the general codes Fluent and Abaqus, with the former used for heat transfer analyses, and a structural FE model including the loading device and complex geometric imperfections was established based on the measured data. Thus, accurate simulation of the out-of-plane behavior of the steel arches at elevated temperature was achieved. On this basis, an in-depth parametric study was carried out to investigate the effects of temperature field variations, load ratio (LR), and geometric imperfection. The analysis results show that FTB occurs at nonuniform temperatures for the arches under concentrated load, and the difference in temperature distribution in fire has a minimal effect on the FTB behavior. LR is negatively correlated with critical temperature; the smaller the LR, the more significant the weakening of critical loads by fire. The effect of initial geometrical imperfections on FTB at elevated temperatures is similar to that at ambient temperatures, and the effect on the critical temperature of FTB can almost be ignored when the imperfection amplitude is less than S/400. [ABSTRACT FROM AUTHOR]

The flexural–torsional buckling (FTB) behavior of a freestanding circular steel I-section arch subjected to static load is systematically investigated under residual stresses, geometric imperfections, and load type effects through experimental and numerical simulation analyses. In particular, a loading rig that allows lateral deformation and twist is designed for the experiment, and a 3D scanner is used to measure the geometric imperfections and the final shape to reflect the out-of-plane buckling response better. The buckling behavior is sensitive to the loading form and the imperfection. Thus, the specific structure of the loading system, complex geometric imperfections based on measurement data, and residual stresses based on roller bending process analysis are included in the finite element model (FEM). The accuracy of the FEM is confirmed by comparing the results with the experimental findings, and a comprehensive parameter study is conducted. Results show that the transition of buckling mode will be caused by out-of-plane geometric imperfections. These imperfections significantly affect the critical load of FTB when the amplitude is greater than S/500, while the residual stress of roller bent arch has a small influence on the FTB behavior. The parametric study also finds that the arch has a large critical load of FTB under nondirectional load compared with directional load. The out-of-plane slenderness ratio, the rise-to-span ratio, and the local plastic zone also significantly affect the FTB behavior. • Experiments on flexural–torsional buckling of fixed–fixed arches are conducted. • The technique of importing complex geometric imperfections into the FEM is proposed. • Imperfection effect on flexural–torsional buckling behavior of steel arch is studied. • Effects of load type and geometric feature on the buckling critical load are discussed. [ABSTRACT FROM AUTHOR]