Pullout strength of headed stud in the longitudinal face of CMU bond beam

[BButler505]

I have a situation where I'm using a wide flange beam as a shear collector for a diaphragm. The beam is parallel to meets a 10" CMU shear wall and I'm going to use the top bond beam to drag the shear into the shear wall. I'm going to weld a plate to the end of the wide flange with 2 headed studs and embed them in the face of the bond beam. My question is how should I calculate the tension pullout strength of the headed studs in the CMU bond beam? I was going to use the ACI 318 equations for concrete breakout strength of an anchor in tension but h.ef is larger than the CMU bond beam.

 

[KootK]

It's tempting to use 318 as the mechanics are surely similar. I never have however. The masonry codes have their own equations for anchors in masonry and I've always assumed that they somehow account for the fact that a grouted masonry cell is a much less homogeneous material than a solid concrete element is. It's those pesky face shells. Another option is to use a post installed anchor in which case you can use Hilti literature etc.

I'm not a big fan of the particular connection and situation that you've described. Even if you can make the numbers work for the drag load, the connection may well yank out when the connected framing undergoes thermal movement during construction. I've seen this in the field more than once on solid concrete walls.

Here's what I'd recommend, in order of preference (strong preference):

1) If aesthetics allow it, bolt a strap plate or angle to the side of the bond beam. Extend the strap to lap with your steel beam and make some kind of slightly eccentric connection to the beam.

2) Cast an embed into the wall that has deformed bar anchors coming off it to effectively lap with the bond beam reinforcing. I'm not really sure how constructable this would be in CMU.

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.

 

[BButler505]

Thanks, I found the equations for the tension breakout strength in ACI530. Our company just purchased the new code book and I didn't know we had it. I had also considered using anangle and welding it to the WF and running it along the face of the shear wall with embedded headed studs as well (your option 1).

 

[Archie264]

>>>It's tempting to use 318 as the mechanics are surely similar.<<<

Wow, I'm more tempted to use the masonry code for my concrete anchors, but, alas, I don't. I wish I could though, what with it being several orders of magnitude simpler. Sigh...

 

[KootK]

I wish I could though, what with it being several orders of magnitude simpler. Sigh...

Couldn't we use the masonry provisions for concrete anchors? Presumably the capacities would be lower but they would surely suffice in many instances. Solid concrete's gotta be an improvement over block/grout composite, right?

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.

 

[Archie264]

Hmm...well, maybe it's possible. I don't know (and wouldn't want to be the test case for finding out) the legalities of substituting ACI 530 for ACI 318 and f'm for f'c though.

 

[wannabeSE]

I am not sure I follow the description. I am assuming the collector and connection are attached at the end of the wall rather than the face of the CMU. If that is the case, you might consider using deformed bar anchors (DBAs) on an embed plate. This can be designed so there is a lap splice between the DBAs and the bond beam reinforcement.

 

[BButler505]

Yes, the beam is at/connected to the end of the 10" CMU shear wall (in the same plane as the shear wall). If you are referring to a connection similar to KootK's option (2) I'm not sure of the constructibility of the connection. There isn't much area in a CMU bond beam for (2) deformed bar anchors plus (2) #5 with standard hooks within the bond beam.

 

[KootK]

There isn't much area in a CMU bond beam for (2) deformed bar anchors plus (2) #5 with standard hooks within the bond beam.

As I mentioned inidially, I also question the contructability of this detail. However, I don't think that the bond beam bars would need to be hooked and I was envisioning a two or three course beam, at least locally, if you pursued this.

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.

 

[BButler505]

The bond beam as we have it now is only one coarse. Also, the CMU walls are quite strong, as we had to design for blast loading due to it being on an airstrip and also on a military facility.

 

[KootK]

It would be a bit brutish but you could also:

1) run your bond beam rebar (weldable) out into space a few feet over over top of the beam.
2) connect beam flange to rebar with a weld plate shipped loose.

The natural bond beam elevation is usually just above the beams anyhow. Field welding access and position issues would require some noodling.

I still like the external angle strap detail the best by far. It could work even if the bond beam went in high/low and you had to fasten to hollow cells.

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.