Beam Bending
Beam Bending
(OP)
It appears that NASTRAN can not compute bending due to an axial load...is this true? For instance, I calculated the deflection of a beam due to a lateral and axial load. When I modeled this in NASTRAN, it seemed to neglect the axial load and only calculate the deflection due to the lateral load. Is there a way around this (I am using CBEAMs). Thanks.





RE: Beam Bending
Sigma bending = Mc/I...no axial load involved, right?
RE: Beam Bending
RE: Beam Bending
RE: Beam Bending
the beam column moment is due to deflection of the beam under lateral loads ... so you'd need to run non-linear nastran to see this effect
RE: Beam Bending
Ed.R.
RE: Beam Bending
Dumb question but is this a 'flag' in NASTRAN where I can enable this option?
RE: Beam Bending
alternatively you can run linear SOL101, then deform your model according to the deflections and run again (and again)
RE: Beam Bending
RE: Beam Bending
what you can do is start with the lateral loads, calc the deflections. these deflections, together with the axial loads, increase the moment in the beam, which increases the deflections ...
so if you model the deflected beam (deflections due to lateral loads) and apply the axial loads to this you'll get larger deflections. non-linear FEM solves this properly, i'm suggesting a way around using NL (since i'm guessing you can't). the difference between these two runs gives you the 1st (largest) amount of deflection due to axial loads (should be less than the deflections due to lateral loads). i'd then model this delfected beam (displace the beam = to the difference between these two runs) ... this is the 2nd order affect of the axial loads, and should be less than the 1st ... etc
clear as mud ?
RE: Beam Bending
RE: Beam Bending
good luck
(look up beam columns in Bruhn, or Niu)
RE: Beam Bending
RE: Beam Bending
RE: Beam Bending
RE: Beam Bending
RE: Beam Bending
again, maybe a few NL runs of differeent times will help you understnad what's going on.
maybe there's another solver out there that'll do both ?
RE: Beam Bending
RE: Beam Bending
Loads on the deformed shape behave significantly different from the same loads on the original shape.
You will need to have a large-deflection switch set.
This will re-apply the loads on the deformed shape (and repeat until answer is sufficient).
RE: Beam Bending
I am basically modeling an accelerating beam under a 1g lateral load.
eelco,
Yep, I quickly found that out and have been able to get the NASTRAN results to match theory but performing a nonlinear analysis w/ large deflections enabled.