×
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

Connection plate eccentricity

Connection plate eccentricity

Connection plate eccentricity

(OP)
I've got a problem where the increased thickness of a connection plate increases the overall eccentricity of the joint, thereby causing the failure of the other plate.

The attached should clarify what I'm trying to explain. It's the fixed base moment of the thinner plate which is theoretically increasing and failing.

Is there a rational explanation why the base moment would not be what it seems, ie. 'axial load x e'?

It seems counter-intuitive that an increase in plate thickness would result in over-stress.

RE: Connection plate eccentricity

I would make the same assumptions you have, so i would end up thickening or stiffening the bottom plate

RE: Connection plate eccentricity

Can you assume the axial load is not at the center of the upper plate, but is closer to the lower plate?  If the upper plate is oversized, perhaps you can assume this.

DaveAtkins

RE: Connection plate eccentricity

Perhaps as the load is applied to the upper plate, and it deflects and rotates, then the load is transferred to the edge of the plate rather than remaining at the centre. Of course at that stage the edge of the plate has moved and so the applied load is still off-centrw and still applies a significant moment to the lower plate.  

corus

RE: Connection plate eccentricity

Quote:

Is there a rational explanation why the base moment would not be what it seems, ie. 'axial load x e'?

Are you looking for a way to justify using a smaller moment at this location?  If the plates are stiff enough to take this moment, then it wouldn't need to go to the connection.  Like if the plate was really a web of a wide flange beam, then you could get by neglecting the moment.  But if you just have two plates, with relatively little stiffness in that direction, then you're looking at a moment of P*e on the connection.

RE: Connection plate eccentricity

I don't know if this solves your question, but try think the "load path" is like - assume loaded in center of the upper plate, then the load is transferred from the center to right side face of the upper plate, then to the welds, then from the welds to the lower plate and to the support. Break the path down, show loads as you go, then sum the forces & moment. Now see what you get.  

RE: Connection plate eccentricity

Based on statics alone your fixed end moment increased 57% I'm not sure why you'd be getting 75% unless you're running a geometric nonlinear analysis and are accumulating P-Delta effects.  

RE: Connection plate eccentricity

The eccentricity is 17.5 which is 75% greater than 10. What am I missing?   

RE: Connection plate eccentricity

whoops, I did punch that in wrong. statics does it.

RE: Connection plate eccentricity

(OP)
Thanks all.

I guess I was clutching at straws. If it was a single connection strengthening the lower plate would be an easy decision, but we have about 500 of these.

I think my best option is to duplicate the existing on the other side of the upper plate. This avoids removing the existing and also eliminates all eccentricity.

RE: Connection plate eccentricity

Yeah that was just a simple statics one there.

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