×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Lateral torsional buckling?

Lateral torsional buckling?

Lateral torsional buckling?

(OP)
I want to calculate Lateral Torsional Buckling capacity moment on ordinary beam with arbitrary section. I don't how to (in SAP):
1) Choose the material (linear, nonlinear...)
2) I think that I must model a beam with Final Elements
2) Apply the loads
3) Apply the supports
4) Which analyse to run
5) How to read the results

Can you help with these basic questions (is there any example).
 

Drile007

RE: Lateral torsional buckling?

It's pretty straightforward to run an eigen buckling analysis in SAP. Go to the Define-Analysis cases menu and add a new case with Buckling as the analysis type. You'll need to specify which loads are to be used for your buckling analysis. Output gives the buckling factors for each mode. You can check the buckling modes graphically using the "Show deformed shape" button, or get them from the output tables.

Buckling factor of 5, for example, means that the load could increase up to 5 times before causing the system to lose stiffness by buckling. You can run the buckling with frame/beam or finite element models.. assuming you meant to say finite elements instead of Final elements

RE: Lateral torsional buckling?

If it's an arbitrary section that will laterally displace and/or twist with any amount of load (i.e. a tiny one), then eigenvalue analysis won't work correctly.  On the other hand, if the beam does have a trivial solution, it will, but you'll have to build up your beam using shells or solids.  Be sure to verify your results A LOT, using beams with known buckling loads, to make sure it's not "garbage in, garbage out."

Keep in mind that your answers will be purely elastic.  In other words, the stress you're getting is the equivalent of Fcr from AISC 2005 Eq. 2-4 for example, NOT a buckling stress or load that accounts for inelastic buckling.  If the stress is high enough, you have to figure out a way to adjust for inelastic buckling and Spec. equations usually provide a fairly easy way to do this.

If you have a system without a trivial solution, your only option is to do a nonlinear static analysis, or a series of them, to determine the buckling load.

RE: Lateral torsional buckling?

(OP)

Thank you 271828,
but you are talking abaut the second step-> how to play with results, but I need information how to "build" correct model (which elements, material, analysis, etc. should I use(run)). Can you recommend me this basic info.

Drile007

RE: Lateral torsional buckling?

More info on your beam?

RE: Lateral torsional buckling?

(OP)

Curently I don't have exact problem, but one day I was wondering about the ∧ and ∨ beam shape. I was thinking about I beam with large openings too...
Thanx 271828 for your attention!

Drile007

RE: Lateral torsional buckling?

Well, in general, you can probably get away with using SAP's shell element.  For example, if you were doing an I-shaped beam, you could build up the flanges and web with shells.

The key to doing anything like this is to start simple and work your way up, verifying that it is doing what you want at each little step.  For example, you can probably find the LTB solution for a rectangle.  Then figure out the LTB for an I-shape.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources