Analysis of local deformation effects in cold-formed tubular profiles subjected to bending

Abstract

Application of high-strength steel can serve improving structural efficiency as well as solve structural problems when traditional materials are inapplicable due to strength limitations. Innovative structural solutions, however, are facing problems related to the absence of corresponding design procedures and reliable constitutive models. Cold-formed profiles are frequently used as structural elements in buildings. The enhancement of a material strength in the profiles with nominal geometry increases slenderness of the cross-section that can cause a local increase of deformations due to high stress concentrations. The increase is a consequence of web crippling often followed by failure of the flange. The investigation of the combined web crippling and flange failure effects is rather complicated due to localized deformed behaviour that is not a trivial subject for experimental identification. The premature deformation increase in a critical cross-section is not necessarily caused failure of the profile that continues to carry further loads. This paper investigates local deformation effects in cold-formed square tubular profiles subjected to bending load. A four-point bending test was used to estimate the effect of local nonlinear deformation on the overall deformation behaviour. The profiles made of high strength steel S700 and S900 grades were considered. Similar profiles made of the steel S355 were tested for the reference. A digital image correlation system was used to monitor deformations of the web surface. A nonlinear finite element model was developed to investigate the local deformation effects on the overall deformation behaviour and load-bearing capacity of the profiles. The model was customized with the reference to the experimental results. After the verification, it was used to illustrate deformation analysis procedure of a continuous tubular beam.