An experimental study of beam-columns subjected to combined torsion, bending and axial actions

This report presents an investigation on the inelastic behaviour of steel I-section beam-columns under combinations of axial load, bending and torsion. The study is motivated by the lack of information on the ultimate capacity of such members, and the lack of design procedures and design provisions. A test facility is built for the testing of the beam-columns, with the primary objective to obtain reliable experimental data for the response for specimens tested at well controlled load- and support-conditions. Tests are carried out for two different Class1 I-sections, the wide flange section HEB 140 and the beam section IPE 160. The behaviour in both uniform and nonuniform torsion is investigated, as well as combinations of bending and torsion at various levels of axial load. Results are given in terms of response histories. Typical beam-column experiments are simulated by means of the general purpose finite element program ABAQUS, using shell elements to model the specimens. The objective is to verify to what extent numerical simulations may replace physical models in studies of beam-columns under similar load combinations. Methods for calculating the full plastic nonuniform torsional moment are discussed. Second order effects are discussed for the combination of axial load and torsion, and simple design interaction equations are proposed. For the interaction between bending and torsion, the applicability of a commonly used quadratic interaction equation is investigated. For the capacity definition, a deformation norm is introduced. An interaction equation on the component level is proposed for the full load combination of axial load, bending and torsion