This technical article deals with the stability analysis of a roof purlin, which is connected without stiffeners by means of a bolt connection on the lower flange to have a minimum manufacturing effort.
The critical factor for lateral-torsional buckling or the critical buckling moment of a single-span beam will be compared according to different stability analysis methods.
The design of a torsional loaded beam according to AISC Design Guide 9 will be shown, based on a verification example. The design will be performed with the RF‑STEEL AISC add-on module and the RF‑STEEL Warping Torsion module extension with 7 degrees of freedom.
As of the program version X.11, the filter options of small compression forces or moments for stability analysis in RF‑/STEEL EC3 have been revised. The revision of these filter options in the "Stability" tab of the "Details" dialog box allows you to work in the module transparently, since they are now independent of the design.
The following structure is covered as Example IV.10 in [1] "Comment on Eurocode 3". For a support with a linearly varying cross‑section, a sufficient ultimate limit state design (cross‑section check and stability analysis) is to be performed. Due to the unequal structural component, it is necessary to perform the stability analysis (from the main support direction) using the method according to Section 6.3.4, or alternatively, according to the second‑order analysis.
This article explains how to determine loads on the basis of the internal force situations defined in the RF‑/STEEL Warping Torsion extension of the RF‑/STEEL EC3 add-on module. Since this new program also allows you to analyze extracted chain-like beam structures in addition to entire chain-like beam structures, it is necessary to determine the loads of the partial structure separately. To do this, a special transformation function has been developed that determines new loads of all partial structures (depending on the internal forces calculated in RFEM/RSTAB) according to each load situation for geometrically nonlinear warping torsion analysis with seven degrees of freedom.
The RF‑/STEEL Warping Torsion module extension of the RF‑/STEEL EC3 add‑on module allows you to design members with asymmetric cross‑sections. The new option is fully integrated in the design module and can be activated for sets of members.