PreTension TieBacks and connectors: Tension only members

Hi,

Can anyone help me with this? Thanks in advance.

We are trying to model and analyze an inclined arch that is supported by a mesh of cables (tension-only elements).

1) How do we define the TieBack and the Hangers as Tension-only elements?

2) How do we pre-tension both the TieBack and the Hangers?

3) Is there a way we can set up the model such that we can find the form of the tension cables?

See attached Rhino file, Grasshopper/Karamba definition, and a screenshot of what we are actually trying to design. Thanks.

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Permalink Reply by Karamba3D on August 1, 2018 at 1:45am

Hi Shivang,

the model shows large displacements because it is kinematic (see attached definition). Sometimes the ThI and ThII solver do not detect such a situation because of unavoidable numerical inacurracies.

Use trusses (like you did ) for the cables, then calculate the structure. Set up a second model where you impose pre-tensioning in case of compression in a cable. You could use the Tension-Compression-Eliminator-component to eliminate cables which are under compression. However I would not recommend this: The procedure is relatively slow because it applies a non-linear, iterative procedure.

For the pre-tension in the cables see the attached definition. You could try to use ThII instead of first order theory (ThI): this takes account of the influence of normal forces on the structural response.

The form-finding of the cables is rather a question of the underlying Grasshopper definition and how you parameterize the position where the cables start and end. Maybe the 'Stitches'-component under 'Utilities' could be useful for you to define the position of the cables. See the manual for details or the examples which come with Karamba in the installation folder (double-click on the Karamba3d desktop icon to get there).

Best,

Clemens

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