Modeling Downstand Beam in Timber Structures 1: Torsion

Tips & Tricks

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Anyone who builds wants to create spaces that are tailored to personal wishes and dreams and express their own way of life. These wishes often include ceilings, whether in residential buildings, office buildings or public buildings, with an enormous span without any support in order to optimally use the space below. However, for reasons of ultimate and serviceability, this requires a very high stiffness of the design. By increasing the beam or plate cross-sections, it is possible to achieve a higher stiffness, but the efficiency decreases due to the increased material consumption. The problem of large spans is often solved with timber or steel downstand beams.

In order to transfer no moments of the floor structure to the downstand beam, "scissor hinges" can be defined in the version with floor beams. In order to consider the same effect also for flat ceilings (e.g. cross-laminated timber), the structural engineer has the option to use "line releases". With these, you can, for example, "release" the degree of freedom phi_x, so that the downstand beam is hinged to the surface about its local x-axis. Thus, the continuous effect of the surface can be represented very easily (without coupling members, etc.).

In the second part of this series, the semi-rigid shear bond between surface and downstand according to the US standard ANSI/AWC NDS and Eurocode 5 will be discussed.


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