Stability criteria for stainless steel equal-leg angle columns

Abstract

Nowadays, the explicit codified criteria for design of centrically compressed stainless steel columns with equal-leg angle sections are absent in Europe. A comprehensive scientific investigation has therefore been undertaken at the University of Belgrade Faculty of Civil Engineering to provide benchmark data for the accuracy assessment of existing column design procedures stated in the European structural steel codes and to propose the new design criteria for stainless steel equal-leg angle columns. A series of experiments followed by advanced and realistic nonlinear finite element studies were performed on pin-ended columns with different lengths to account for both elastic and inelastic failure characteristics including minor-axis flexural and flexural-torsional buckling modes. The systematic experimental programme involved tensile material tests, geometric imperfection measurements, residual stress measurements and in total 63 column compression tests, considering two stainless steel alloys, lean duplex grade EN 1.4162 and austenitic grade EN 1.4301. Three different production routes, including cold-formed, hot-rolled and laser-welded angles were studied to quantify the effects of pronounced material nonlinearity and initial structural imperfections — residual stresses and geometric out-of-straightness on their buckling regimes and ultimate capacities. The behaviours and compressive capacities of the studied columns was confirmed to be dependent on not only the column slenderness, but also the elastic torsional-flexural buckling load-to-the elastic minor-axis flexural buckling load ratio. Similar to the previous research, it was demonstrated that in equal-leg angle columns, torsional and local buckling are essentially two designations of the same phenomenon. The research gathered a large column ultimate strength data bank that includes experimental values, also collected from the literature, and numerical values. The merits and accuracy of the proposed design criteria were assessed through the statistical data estimation and the reliability analysis to evaluate the safety factors and compare with the currently recommended by European stainless steel structural code.