Experimental and numerical investigations on flexural-torsional buckling of roller bent steel I-section arches

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.