In the case of open cross-sections, the torsional load is removed mainly via secondary torsion, since the St. Venant torsional stiffness is low compared to the warping stiffness. Therefore, warping stiffeners in the cross-section are particularly interesting for the lateral-torsional buckling analysis, as they can significantly reduce the rotation. For this, end plates or welded stiffeners and sections are suitable.
When modeling a reinforced concrete rib with a masonry wall above, there is the risk that the rib is underdesigned if the structural behavior of the masonry is not correctly considered and the connection between the masonry wall and downstand beam is not modeled sufficiently accurately. This article deals with this issue and shows the possible modeling options of such a structure. In this example, the reinforcement is determined only from the internal forces and without secondary minimum reinforcement.
As gravity loads act on a structure, lateral displacement occurs. In turn, a secondary overturning moment is generated as the gravity load continues to act on the elements in the laterally displaced position. This effect is also known as "P-Delta (Δ)". Sec. 12.9.1.6 of the ASCE 7-16 Standard and the NBC 2015 Commentary specify when P-Delta effects should be considered during a modal response spectrum analysis.
Fin plate connections are a popular form of pinned steel connection and are commonly used for secondary beams in steel structures. They can be used easily in beam structures arranged on the top edge (for example, working platforms). Manufacturing expenditures in the workshop as well as the onsite assembly costs are normally manageable. The design seems to be completed easily and quickly, but it has to be put into perspective to a certain extent in the following text. Moreover, this connection type is basically possible as a pinned beam-to-beam or pinned beam-to-column connection; the former case is the more common one in design practice.
The secondary reinforcement according to DIN EN 1992-1-1 9.2.1 is used to ensure the desired structural behavior. It should avoid failure without prior notification. The minimum reinforcement has to be arranged independently of the size of the actual loading.
This example is described in technical literature [1] as Example 9.5 and in [2] as Example 8.5. A lateral-torsional buckling analysis must be performed for a principal beam. This beam is a uniform structural member. Therefore, the stability analysis can be carried out according to Clause 6.3.3 of DIN EN 1993‑1‑1. Due to the uniaxial bending, it would also be possible to perform the design using the General Method according to Clause 6.3.4. Additionally, the determination of the critical load factor is validated with an idealized member model in line with the method mentioned above, using an FEM model.
For structural reasons, shear connections usually include fin plates or flange angles. Main and secondary beams arranged on the top edge require notching or long fin plates. Hinged end plate connections are often welded to the web.