×
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

Modeling of bolted supports

Modeling of bolted supports

Modeling of bolted supports

(OP)
I have always modeled bolted supports using fixed boundary conditions. For example, lets say I want to do an FEA model of a cantilever beam type structure that is bolted to the wall. I would start by using beam elements and fixing the end that is attached to the wall.

Recently I wrote a structural analysis report for a structure that is bolted to the floor. At the locations where the bolt holes are I applied fixed boundary conditions. The engineer who reviewed the report for the customer commented that the fixed supports I used for the bolts should be changed to pinned supports and the model re-run.

I can't really rationalize how this is a pinned support. If there were one blot I suppose the the structure could rotate around the axis of the bolt. However, with 4 bolts that motion is restricted. I would also assume that the head of the bolt can carry some moment when the load is along the axis of the bolts.

So which is correct, pinned or fixed for bolted connections?

RE: Modeling of bolted supports

It should not make much of a difference, since the moment is largely reacted by a couple of the fasteners. Provided the coupling distance is relatively large, there should not be much moment in the fastener even if you do fix it. The reality is that the fastener is somewhere in between...so I would take the most conservative approach, which is probably to just assume it is pinned.

Brian
www.espcomposites.com

RE: Modeling of bolted supports

The worst case for assessing the beams would be to assume pinned members. The worst case for assessing the bolts would be to assume the beams were built in and the bolts had to carry the bending moment. The true case would be somewhere inbetween. I'd run both cases and report on each.

RE: Modeling of bolted supports

there a couple of things here. i think the reviewer said that your "monument" shouldn't be fixed at four points to the floor to the plane. Very correct, if you do this then 9g fwd creates a large lateral couple +ve on one side, -ve on the other (so internally reacting); and if they're single bolts (or closely pitched bolts) they probably wouldn't react much moment. Instead i think you should model the attmts as three rods (aligned X, Y, and Z), and the far end of the rods is a ground. Next you'll ask "how stiff ?", and I'd answer pretty much any stiffness, i like 1in2, but the difference should be small (try different areas 1in2, 0.1in2, ...)

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