wood truss structure
wood truss structure
(OP)
I'm quite new in FEM and want to calculate wood truss structure (beam elemnts). But I have no iedea which values should I use for my structure to define properties, because wood is 3D orthotropic.
Thanks a lot.
Thanks a lot.





RE: wood truss structure
Ed.R.
RE: wood truss structure
RE: wood truss structure
RE: wood truss structure
RE: wood truss structure
Beams and trusses, while they appear similar, are analytically different by the "degrees of freedom" for each element. Search this forum, I'm sure someone has probably written a dissertation on degrees of freedom.
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
www.borowskiengineering.com
RE: wood truss structure
I think you can use either beams or truss elements and if modeled correctly they will give similar results for your structure...In any case don't believe any results using the values Nastran is complaining about....The results are garbage....
Ed.R.
RE: wood truss structure
RE: wood truss structure
Strictly speaking wood is not a isotropic material, therefore G = E / (2(1+v)) does not apply. Depending on the direction you study compared to the fiberdirection the E-module varies, a lot.
What you need is a 3d anisotropic material model, or some simplifications.
You say truss, that means that E-module parallel to the fibers (typically the "highest" value) is what you need.
G controls shear deformation, not a very significant parameter for a truss.
Finally v, also not that important for a truss. It is typically 0.025 or 0.4 depending on fiber direction. Say 0.025, calculate G as for the isotropic material using a correct value for E.
I don't think you will be too far from the truth. Also, Nastran (at least the MSC flavour) as far as I know uses the values you input. It's complains if isotropic relation is "violated" but nothing is changed in the numbers. "Garbage in, garbage out".
Good Luck
Thomas
RE: wood truss structure
I doubt the material property of wood would have so much stand deviation, which makes numerical computation meaningless. Am I right?
RE: wood truss structure
If this is as simple as a house roof truss, I would suggest calculating it by hand. A complicated building truss, FEA could speed things up.
RE: wood truss structure