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Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

(OP)
Hi

Does anyone have any recommendations as to how to prevent side-face blowout of an anchor bolt near a free edge? I cannot increase the pier size as I am stuck with arch requirements nor can I reduce the bolt length. Can I add stirrups @ 3'' spacing and call it good? Can the stirrups even help in preventing side face blowout? ACI code does not mention anything about reinforcement for side-face blowout. How do I prevent this?

Thanks

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Can you provide some geometry and loads so we can get a context for the problem? (#3's might not be enough)

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

This has been discussed a great bit on this site. One example is: Link

A lot of engineers do ignore side face blowout when they detail the anchorage and rebar to develop Fy. As long as all other limit states are precluded, I don't have much concern over sideface blowout most of the time.

Also, what about switching to non-headed anchors?

"It is imperative Cunth doesn't get his hands on those codes."

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

(OP)
The loads are huge. They are in terms of 1000kips. This is a building in SDC D. I am confused. Few say we can use reinforcement to prevent side-face blowout and others no for side-face blowout.

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

BAGW,

Are you looking at side face blowout due to anchors in tension? If so, KootK has a document that deals with edge distance, reinforcing, and blowout.

(Upon carefully reading your title, I see that anchors in tension is indeed the case)

Hopefully he will stumble across this thread.

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

winelandv - that document is in the thread link I provided.

BAGW - 1000 kips of tension?? I think that falls outside of typical conditions. Read the PDF in the thread link I provided. If you feel it is needed, you can use a strut and tie model to restrain the blow out spall.

Why not mechanical couple instead of using headed anchors?

"It is imperative Cunth doesn't get his hands on those codes."

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Reinforcement does not prevent side-face blowout, only maintains the load after crushing of the concrete. This is why ACI has requirements for shear reinforcement and tension reinforcement. You are going to have to start considering using reinforcing, we dont know your configuration but with a 1000kips its hard to understand how you dont have sufficient concrete with the loads.

Thread with detail

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

I don't see why hairpins would not work to take the tension -

Mike McCann, PE, SE (WA)


RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

I echo sandman's sentiment regarding sustained bolt tension loads. That is a good reason to design anchor head confinement.

Quote ((DeVries et 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.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Quote (msquared48)

I don't see why hairpins would not work to take the tension -

Side-face blowout is a localized fail of the concrete in crushing, projecting from the head towards the near face. I would say that we are likely never going to get design criteria allowing full tension transfer to reinforcement. It is possible with additional testing we may get an increase to the loads, I doubt it will be what people want it to be.

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

BAGW - In the Widianto et al. article referenced above they note that the research indicates side-face blowout failure can be precluded for an edge distance greater than 4.8 anchor diameters. Do you at least have that?

Is your tension the result of net uplift or moment at the base? If it is from moment at the base, you might consider treating the pedestal as if it were an exterior roof level beam-column joint and detail the transverse reinforcing to satisfy ACI 352R. Testing has shown that Appendix D is overly conservative when used to calculate the capacity of headed bars in this condition, likely for two reasons: (1) the joint is well-confined with transverse reinforcing, (2) the head is anchored within the diagonal compression strut.

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

Seriously? 1000 kips? Have you checked the math? Sure there's not a mistake there somewhere?

RE: Anchor side-face blowout in tension. Ways to prevent it without increasing the edge distance?

I believe the only two ways to increase side face blowout strength is either to increase the bearing area of the anchor or increase the concrete strength. Adding additional rebar doesn't help you with side face blow out (it will help you quite bit with concrete breakout tension/shear). Based on past experience I have found that increasing the bearing area from a heavy hex nut to a plate washer is most effective. This will also help you with anchor pull out. Make sure to maintain proper clear cover and I generally like to make sure there is proper distance between the plate washers and column reinforcing. Size the area of the plate washer to handle the side face blowout. You will find little guidance on determining the thickness of the plate washer. You can either run a simple conservative one-way bending check with maximum anchor tension or a finite element mesh if you want to size it spot on. I usually default to 50 ksi steel plate and run a simple conservative one-way calculation: this generally produces a healthy capacity that doesn't look overly large compared to 36 ksi steel plate. I have seen columns with roughly 1000 kips tension in SDC C. If I remember correctly they were 2-1/2" diameter, grade 105, with large plate washers at the bottom of the anchor. As for my last bit of advice if you are in SDC D, keep an eye on all of the ACI Appendix D seismic requirements.

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