×
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

Appendix D - Side-faced Blowout question

Appendix D - Side-faced Blowout question

Appendix D - Side-faced Blowout question

(OP)
I'm checking the design for a gate post on a pedestal. The designer didn't check for side-faced blowout or pullout. He needs deeper bolts but the problem is the blow-out. The pedestal is trapezoidal in plan. It's about 3" shy of the code requirement on one side. They can't be widen the pedestal because there's a wall on one side and the road width can't be narrowed. Rather than waste time with trying to play around with the layout of the post base plate, my thought is to use supplemental reinforcement - closed hoops. ACI doesn't explicitly address this but I could argue that it's same situation for concrete breakout. Is that a fair argument?

I also had a crazy idea: Assume that the wall against the pedestal will prevent a blowout but I can't talk myself into that one.





RE: Appendix D - Side-faced Blowout question

For side face blowout, you want reinforcement very close to the anchor head. Spiral reinforcing around the anchor heads may be the way to go. You typically provide for a transverse tensile capacity of about 1/4 the anchor tensile force. See this paper for some discussion of that: Link



Quote (Bridgebuster)

I also had a crazy idea: Assume that the wall against the pedestal will prevent a blowout but I can't talk myself into that one.

I'm flip floppy on that too. How will the pedestal be attached to the wall?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Appendix D - Side-faced Blowout question

ACI appendix D does not address supplemental reinforcing for side face blowout. Based on the PDF KootK supplied my guess would be that, the ties do not increase the strength but help maintain strength. " Cannon et al.(1981) recommended spiral reinforcement around the head. It should be emphasized that transverse reinforcement (ties) did not increase the side-face blowout capacity (DeVrieset al. (1998)). Large amount of transverse reinforcement installed near the anchor head only increased the magnitude of load that was maintained after the side-face blowout failure occurred." If you fail for side-face the ties wont increase the load allowable.

RE: Appendix D - Side-faced Blowout question

(OP)
Thanks for the responses.

KootK - if I go with the crazy idea I thought about drilling and grouting some L shaped bars or some hairpins.

RE: Appendix D - Side-faced Blowout question

That's an interesting perspective sandman. Are you considering spiral reinforcing to be the same thing as tie reinforcing in this regard? I have not been but that's just interpretation I guess. Some additional thoughts:

- One the one hand, like most reinforcing, I wonder if spirals do anything at all until after the blowout has occurred.

- On the other hand, the reference document specifically mentions that the 1/4 T numbers come from consideration of the Poisson effect in concrete. To me, that kind of suggests actually improving the breakout capacity. I've always been a bit fuzzy on this aspect of it.

- In a sense, who cares if you get side face blowout? Post blowout, you've still got your load carrying mechanism for the most part. I would care with respect to aesthetic and durability issues in many cases of course.

Quote (Bridgebuster)

KootK - if I go with the crazy idea I thought about drilling and grouting some L shaped bars or some hairpins.

Gotcha. In my heart of hearts, I feel that this would probably be just fine. Theoretically, I suppose that one ought to design the connections in the vacinity of anchor head for 1/4 x T as well.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Appendix D - Side-faced Blowout question

I dont have access to the papers referenced in your doc. But going off the section from the PDF and based off my understanding of side face blow it makes sense that providing ties; spiral, square, etc. would have minimal impact on improving the strength but would minimize the strength loss. The side face blow is a narrow failure cone localized at the head and projecting out to the side, my guess is the ties would help restrain the concrete pieces after failure but would not be mobilized until that happens. Post blow out you have a significant reduction in the concrete breakout, as you have lost head engagement of the anchor and would be utilizing the threads for a transfer mechanism.

RE: Appendix D - Side-faced Blowout question

I think that an interesting analog is the spiral bursting reinforcement used behind post tension anchorages. There, you're seeing most of your design load in early age concrete. And you seem to get no failures nor even cracking

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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