Through-Bolt In Hollow CMU 2

[BSVBD]

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!

 

[dcarr82775]

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.

 

[XR250]

this was discussed recently

http://www.eng-tips.com/viewthread.cfm?qid=383736

 

[KootK]

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.

 

[msquared48]

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

Mike McCann, PE, SE (WA)

 

[XR250]

I would not attempt 2000 plf even with a grouted cell

 

[RFreund]

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

EIT

http://www.HowToEngineer.com

 

[KootK]

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.

 

[XR250]

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.

 

[KootK]

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.

 

[RFreund]

@XR250 - Nice.



EIT

http://www.HowToEngineer.com

 

[Guastavino]

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".

 

[XR250]

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