×
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

Base Plate Prying Action?

Base Plate Prying Action?

Base Plate Prying Action?

(OP)
When you've got an angle or a tee section supporting a tension load, you have to amplify the bolt forces for prying action.

Is there a similar need for bolt amplificati0n when designing anchor bolts in fixed base plates where the anchor bolts provide a tie down force for the base plate?

Obviously there is SOME prying action due to the 1.5" or so base plate overhang.  Perhaps, since concrete is considerably less stiff than steel, this makes the prying effect insignificant?

Thanks,

Kootenay

RE: Base Plate Prying Action?

With the way people usually determine the plate thickness, there's no need to consider prying action.  The usual assumption is that "failure" equals a single yield line forming at the flange adjacent to the tension rods.  Prying action will only happen if the plate is made thinner, so a second yield line is required to resist the load--the second one will be at the bolt lines.  If I was going to try to really design base plates to the gnat's butt, I'd use the AISC DG16 (or maybe 4) and use their procedure that includes prying action.  It would have to be adapted a little for use with base plates, but this would work.

RE: Base Plate Prying Action?

(OP)
281828,

Thanks for your post.

I'm doing something a little unusual with this.  I'm elongating my base plate and making it as thin as possible in order to make the connection more flexible and minimize the tension in my achor bolts (long story).  This is how I've come to be concerned with prying action.

I've always been curious about yield line design in steel. I'll check out the design guides that you recommended.

Kootenay

RE: Base Plate Prying Action?

"tie down force" implies a tension load on the fitting, no?  i would analyze like a Tee fitting under tension.

RE: Base Plate Prying Action?

(OP)
I gave that a whirl Aerospace.  It triples the bolt force.  Additionally, the AISC procedure doesn't account for the fact that the material pried against is concrete, not steel.  Maybe it doesn't matter, I'm not sure.

RE: Base Plate Prying Action?

K-kid, You mentioned a base plate. Is this a column on a footing. If so they will probably double nut it for erection and mess up your assumptions. Maybe limit the base plate grout to the area between bolts, or just under the column. this could become a strange looking detail.

Old CA SE

RE: Base Plate Prying Action?

(OP)
This is a column on a footing.  I thought about the limiting the grout to the area between bolts too.  Trouble is, I need to get some serious shear out of the bolts too...

RE: Base Plate Prying Action?

I put this in the wrong thread somehow earlier:

I had to do a yield line analysis for a column cap plate on an existing building once.  It was terribly overstressed using elastic analysis (450%), but using yield line analysis knocked it down to around 125%.  I was quite impressed with that.  I guess that's the extra capacity you get out of 4 yeild lines.  

Anyway, the point was that I used the procedure outlined in my concrete text (McGregor/Wight), because I couldn't find any easy to follow references for steel.  The concrete example was easy to follow and implement.  

RE: Base Plate Prying Action?

You might try out the new Hilti Profis 2.0 software available for free on their web site.  I believe it allows you to have a baseplate on concrete or on leveling nuts.

_____________________________________
I have been called "A storehouse of worthless information" many times.

RE: Base Plate Prying Action?

Any thought to a shear key to help out your anchor rods?


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

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