Study on the out-of-plane stability of steel portal frames

Within the current EN 1993-1-1 the verification of rafters of portal frames for lateral-torsional buckling in the haunched portions loaded by hogging bending moments is not clarified. Recently the authors have conducted an extensive theoretical analysis programme on lateral stability of steel portal frames of hot-rolled profiles. Special software has been developed for automatic modelling and applying both the GMNIA and the general method for lateral and lateral-torsional buckling. To validate the numerical simulations, an experimental programme has been conducted on three typical portal frames of hot-rolled profiles. It has been proven that the results by GMNIA comply well with the tests, therefore is adopted as benchmark method of numerical analysis. An extensive parametric study is then conducted on thousands of portal frames composed of hot-rolled profiles. An important finding based on the comparative analysis is that the application of the general method to whole portal frames appears non-conservative and therefore its use shall be limited to single members. Based on the obtained results, simple design rules for practical application are suggested by adapting the well-known equivalent compressed strut model.