Modeling Downstand Beam in Timber Structures 1: Torsion

Modern buildings are designed with spaces tailored to personal desires and dreams, expressing individual lifestyles. These requirements often include ceilings—whether in houses, office buildings, or public buildings—that have an enormous span and no support, allowing optimal use of the space below.

However, this requires a very high stability level for load‑bearing capacity and serviceability reasons. By extending the size of beam or plate cross-sections, you can increase the stability, but the cost effectiveness decreases because of the additional consumption of material. One common solution for these large spans is to use timber or steel downstand beams.

To prevent transferring moments of the ceiling structure on the downstand beam, you can define "scissors releases" when using ceiling beams. In order to consider the same effect in the case of a flat ceiling (for example, cross‑laminated timber), you can use the "Line Release" option. Mit diesen kann beispielsweise der Freiheitsgrad φ_x "freigegeben" werden, womit der Unterzug um seine lokale x-Achse gelenkig an die Fläche angeschlossen ist. Damit kann der Durchlaufeffekt der Fläche sehr einfach (ohne Koppelstäbe usw.) abgebildet werden.

The second part of this post will describe a semi‑rigid shear coupling between the surface and the downstand beam according to American standard ANSI/AWC NDS and Eurocode 5.

Author

Mr. Rehm is responsible for developing products for timber structures, and he provides technical support for customers.

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