Experimental Investigation into Flexural-Torsional Ultimate Resistance of Steel Circular Arches

Abstract

This paper deals with experimental investigations into flexural-torsional ultimate resistance of in-plane-pinned circular steel arches. Three I-section arches with the same span but different rise-to-span ratios were tested under different loading conditions. A test rig comprising loading frames and lever beams was used to apply symmetrical three-point loads over the full span and unsymmetrical two-point loads over half the span to the arch rib. These concentrated loads are directed toward fixed points during flexural-torsional buckling of the arches. The arches are supported in such a way that their ends in plane are pinned and out of plane are semirigidly restrained. Geometric imperfections are measured before loading. The test results show that when the test arches reach their load-carrying capacity, plastic zones form in the arch rib, and the out-of-plane flexural-torsional deformation is significant. It is found that the pinned arches buckle in an asymmetric double-wave S-shaped flexural-torsional failure mode as a result of the semirigid restraints for bending out of plane at arch ends, rather than in a one-wave C-shaped buckling mode for rigid restraints. Comparisons between the experimental and numerical results indicate that the finite-element method developed in the paper can predict the inelastic flexural-torsional response of steel arches very well.