P 840 – On the stability of uniform and non-uniform Ibeams under bending – Design aids for the simplified stability check
Portal frame structures made of steel mostly comprise open, I-shaped, hot-rolled sections. Often the depth of the rafter is increased near the eaves by a haunch toapproximate the load distribution. This design offers the economic advantage that a smaller section can be used for the largest part of the member.
In the current standards proof formats are specified for check of out-of-plane stability, that means lateral torsional buckling, that are based on the determination of the elastic critical buckling moment of a cut-out member. The member capacity is then calculated using a buckling curve based on experimental and numerical simulations. For the check of uniform members, design aids are provided in technical literature. The lateral torsional buckling of haunched members is only covered for special cases and not in a satisfactory way.
Within the FOSTA research project P 690, design aids were developed that present the results of numerical calculations and experimental tests in a revised form for use with the simplified stability check. In the present report, these design aids are compiled in a way that enables the engineer in daily work to perform the lateral torsional buckling check of I-beams with and without haunches. For this, the design aids are reprocessed so that all necessary information for the simplified stability check can be found quickly and easily.
The design aids include diagrams and formulas for calculating the ideal critical buckling moment Mcr for members with non-uniform cross sections. Recommendations are given for the choice of the appropriate buckling curve. In addition, calculation tools for considering secondary components such as purlins, bracings and sheeting are provided. Furthermore, rules for breaking down structures into individual members are specified.
The present report comprises the design aids whichare summarized in the annex in a compressed form. Within the text part the necessary background information is given. The use of the design aids is presented by means of flow charts and a worked example.
The research project was carried out at Lehrstuhl Stahlbau, Technischen Universität Dortmund. FOSTA has accompanied and funded the research work.
Only available in german language.
D. Ungermann, I. Strohmann