Prestress multiple members

Hi,

I'm uning Karamba 1.0.5 and I'd like to assign prestress values to multiple members to let them change their length. The members are fully constrained at one end, at the other end they are partly supported, so the extentions is not inhibited.

I set up a test model that works fine with theory I. order solver. The large def solver however gives erratic results as the members extent more that it was defined. This causes a real problem in the model I am presently working on.

Please see attached file. Can anyone help me, please?

Thanks and have a nice day

Michel

140223_kara%20prstrs%20lst%20prblm.gh

Replies to This Discussion

Permalink Reply by Karamba3D on February 23, 2014 at 2:34pm

Hi,

the large deformation analysis in Karamba 1.0.5 is purely incremental and meant for form finding.

The load gets applied to the model in several steps. For each load step nodal displacements are calculated and nodal positions updated correspondingly. This new model forms the input for the next step and so on. Member forces do not enter the update mechanism (see manual) therefore no cross section forces or support reactions result at the end of the process.

The reason why your total deformation under initial strain comes out larger than expected is that the strain increments get applied to increasingly longer members. For large strain the correct measure is not (L-L0)/L0 (L..deformed length, L0...initial length) but ln(L/L0). In your case this is ln(1.646/1.0) ~ 0.5.

Best,

Clemens

Permalink Reply by Michel on February 24, 2014 at 11:35pm