Initial strain affecting stress but not deformation

Hello,

I am working on a tensegrity roof project that is composed of 12 beams of 12 tensegrity modules each. For each beam, we use pretensioned cables to counter the uplift caused by wind loads.

I applied wind loads as a point-load on each tensegrity module (144 total), and the initial strain on the cables only (see attached file).

However, the analysed model shows that whatever initial strain is applied on the cables, it only increases the internal stress, and does not reduce the deformation of the structure.

Any idea how to solve this?

Thanks!

Philippe

Attachments:

TensegrityRoof.gh, 118 KB

Replies to This Discussion

Permalink Reply by Karamba3D on April 8, 2017 at 4:06am

Hello Philippe,

use the 'ThII Analysis'-component in order to include the geometric stiffness which comes from tensioning the elements.

With 2nd order theory enabled the beam elements in Karamba may show convergence problems in case their axial force NII is verly large. When this happens switch to truss elements by disabling the cable's bending stiffness.

I think your model contains duplicate nodes.

In case you want to have tensile stresses in the cables use a positive prestrain.

Try to reduce the complexity of your geometry as much as possible for testing.

Best,

Clemens

Permalink Reply by Philippe Lalande on April 8, 2017 at 7:47am

Thanks you for your reply. Using ThII Analysis did indeed correct the stiffness of the cable elements due to initial strain, and by switching them to truss elements, as you mentioned, the deformation is now plausible.

Cheers,

Philippe

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