×
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

Through-Bolt In Hollow CMU
2

Through-Bolt In Hollow CMU

Through-Bolt In Hollow CMU

(OP)
Does anybody "Through-Bolt" to support ANYTHING in hollow CMU?

Occasionally, the client, the GC, wants to support the new roof structure, with a continuous steel angle, "through-bolted" to the existing hollow CMU.

The typical load scenario is anywhere from 600-2,000 PLF (DL+SL)

Throughout the past twenty years, I've always been able to convince them that it won't support the newly imposed load. But, at least once a year, the request is still made. I typically will specify a HILTI Adhesive w/ Mesh Screen, or inject grout into the existing cores through drilled holes, or insist that a column and beam line or stud-wall are necessary, all depending on the amount of load.

I do not believe that the bolt connection to the opposing face-shell of CMU possesses any credible value. In fact, I believe, it even imposes uplift.

Is there something I do not understand?

Thank you!

RE: Through-Bolt In Hollow CMU

I think a thru bolt is worth more than a hilti screen tube epoxy anchor. I think the thru bolt is locally less demanding on the wall than the epoxy anchor which requires the entire force couple to occur in one face shall.

RE: Through-Bolt In Hollow CMU

I always use the screen tube systems. My primary motivation is that testing has been done to support the design values. While I have some ideas about how to calc out through bolt capacity, I've never seen an accepted method presented nor any testing results. I once designed a lifting lug using first principles. I later found out that there was standard for such a thing and my design was out by a factor of two. I prefer to use methods that have been vetted my cohorts.

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: Through-Bolt In Hollow CMU

Thru - bolt is fine, but I would grout the cell too.

Mike McCann, PE, SE (WA)


RE: Through-Bolt In Hollow CMU

I would not attempt 2000 plf even with a grouted cell

RE: Through-Bolt In Hollow CMU

Do you really think a screen tube would perform better than thru bolts?

EIT
www.HowToEngineer.com

RE: Through-Bolt In Hollow CMU

For both systems, in tension, you pull against one face shell. Tie.

For both systems, in shear, you basically deal with all of the shear at the load side face shell. With the through bolt, you've got dowel bearing in an oversized hole. Infinite stress, a little crushing, things settle down. Real potential for a fracture mechanics style failure. With the screen tube, you've got dowel bearing on an oversized hole with some spiffy grout in the interstitial space. Point screen tube.

Eccentricity is clearly bettered handled by the through bolts as mentioned above. Point through bolts.

Yeah, I would put my money on the screen tubes.

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: Through-Bolt In Hollow CMU

What about cutting a screen tube to CMU depth AND using it with a thru bolt? Best of both worlds.
Would also give twice the pullout as it would use both face shells.

RE: Through-Bolt In Hollow CMU

Quote (XR250)

What about cutting a screen tube to CMU depth AND using it with a thru bolt?

Hell. Yeah.

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: Through-Bolt In Hollow CMU

Quote (XR250)

What about cutting a screen tube to CMU depth AND using it with a thru bolt? Best of both worlds.

Great idea. Company I used to work for did this. Only thing is, I wouldn't count on it for capacity. This assumes you have a contractor that will do this correctly. Not to be cynical, but I wouldn't want to put my neck out there assuming that the contractor can easily construct what you're looking for when it's not an industry standard installation. Now, belt and suspenders approach, sure. But if the numbers were close, I wouldn't personally take the risk.

I guess you could have them load test a percentage of them, which might would make me feel more comfortable.

Also, I wouldn't thru-bolt unless it's grouted. I just imagine a potential for the masonry to crack when the nuts are tightened. Not saying it will happen, but again, I don't trust contractors for things that aren't typical.

In summary, if you get a screen anchor to work numbers-wise, I'd go with that because you have code approved numbers to stand on. I tell clients all the time that "that probably works in the real world, but not in the code world".

RE: Through-Bolt In Hollow CMU

You are assuming we can count on ANY contractor to install epoxy anchors correctly :>

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