FEM for form-finding membranes

SOFiSTiK SOFiPLUS
1

Hello,

  1. I was wondering what FE method does sofistik use to analyze tensile membranes (transient stiffness or Newton-raphson etc… for both form-finding and static analysis)? I can see in the ASE manual you guys mention that DR is not used.

On pg 59 of the english ASE manual this sentence with “mostly” confuses me whether these listed nonlinear FE analyses are applicable to the form-finding or exclusive for wind analysis:

“Further textile properties are realized mostly by a simplified linear- elastic orthotropic material law. So when the membrane has its normal stiffness e.g. in a final wind analysis, SOFiSTiK makes a normal geometric nonlinear FE analysis (Newton Raphson and Crisfield or line search residual force iteration)”

  1. I saw your membrane video on youtube and it was very helpful, however I’m not sure where the .sofistik file the gentleman refers to open is?

Any info or help would be greatly appreciated♡! Thank you for your time and patience!

2

Hello,

SOFiSTiK “use[s] for formfinding the normal geometric nonlinear FE analysis with residual force iteration but with nearly zero stiffness in the mebrane” (SOFiSTiK ASE manual, 2-50).
This means you have to start the formfinding with an ASE run with the described settings:

+prog ASE
HEAD …
SYST PROB TH3 NMAT YES
GRUP 1 FAKS 1e-10 PREX 2 PREY 2 $ membrane prestress of 2 kN/m
…

In a next step you have to substitute the original system for the deformed system:

+prog ase
HEAD
SYST PLC 2 STOR YES
END

Now you can apply loads with SOFiLOAD and calculate the deformed system with a nonlinear FE analysis.

SYST PROB TH3 PLC 2 NMAT YES

I don’t know if the example file still exists. I suggest to look at the the TEDDY examples about membranes:

TEDDY > File > examples > ASE > english > membranes > e.g. atrium.dat

Best regards
Frederik Höller
Your SOFiSTiK Support Team