Fire cut beam ends in concrete walls; Are they required??? 2

[SRO]

I'm designing a new residential structure and the architect wants concrete walls (interior & exterior) all the way to the roof. These walls will support beams bearing in beam pockets at mid-height of the concrete wall. I was going to specify that the beams have fire cuts at the ends (similar to a beam bearing in a masonry wall pocket) but there is a distinct lack of information on this condition. Is this not necessary with concrete walls due to the reinforcing? Has anyone come across this that can chime in for me?

 

[phamENG]

The whole point of the 'fire cut' is to allow the wood member to rotate out of the pocket during a collapse and prevent it from pulling the wall down. If you've got a 20' floor span and a fire against the far wall, you could conceivably end up with a 16' foot cantilevered floor hanging onto your wall. That could be a problem even for a reinforced concrete wall.

The real question is do you need it? Are these fire rated party walls intended to remain standing when one adjacent unit burns and collapses? If not, then you probably don't need it. You don't say what kind of residential structure you're designing, or the code to which you are designing it.

You also need to think about constructibility. Those pockets in masonry walls were possible because, when the wall got to the bearing height, they would frame the floor and then keep going with the wall. What kind of lifts will the concrete contractor want to do on this building? Will they match up nicely with beam bearing elevations? My guess is no. And even if they did, coordinating the framer and the concrete sub probably won't be fun. I wouldn't be surprised if the framer were to show up to find a nice pocket at each end that he can't put the beam in without cutting it in half. One option could be embedded steel plates that could have a bearing seat welded on after the wall is up. For joists, a ledger bolted to the wall would do.

 

[SRO]

It is a single family residential structure designed using IRC-15

we are using ICFs for the exterior walls and regular forms for the interior walls. The maximum point load (Pu) is 22 kips. I like your embedded plates idea and I'll use it if I have to, but I think it would be easier for the contractor to form a beam pocket.

Joists are all hung from a ledger board bolted to the side.

 

[JStructsteel]

If you fire cut your beam, then will shear be an issue? I have never seen it in concrete.

 

[phamENG]

Fire cuts can cause shear issues, but there are design provisions for those to overcome them.

No need to fire cut it in a single family residence unless there's some abnormal design criteria (maybe a panic room/storm shelter in the middle of the house that needs to survive when the rest of the house comes down).

Just be careful with the pockets - make sure there's room to get the beam into both pockets without cutting it.

 

[dhengr]

SRO:
You said, 8SEP22, 17:13..., “we are using ICFs for the exterior walls and regular forms for the interior walls. The maximum point load (Pu) is 22 kips. I like your embedded plates idea and I'll use it if I have to, but I think it would be easier for the contractor to form a beam pocket.
Joists are all hung from a ledger board bolted to the side.”

You better pay very close attention to all of your detailing and have a full understanding of all of the particulars of the ICF system you are using. While these are an interesting wall forming system for a lightly loaded, uniformly loaded wall, they are not without their difficulties in terms of installation of the forms plumb and in a straight line, and being held/braced that way during the grouting process and curing. They have some problems with complete and proper grouting and consolidation unless special care is taken, without leaving unwanted (and difficult to see) voids in the concrete fill.

22kips is probably a fairly significant concentrated load on an ICF’s honeycombed conc./void semi-solid core. And, any embedded stl. pls. or bearing pls., pockets, and the like are not quite a simple as just nailing the pls. to the face of a conc. form. Getting much concentrated vert. rebar into a confined conc. column space requires spacial detailing, as does the spread of a concentrated load under a beam pocket, and the like.

Any ledger supporting joists or light beams will need some special detailing attention. I would not just paste the 2x ledger to the face of the crumbly foam insul. forms. And, remember that the ledger A.B’s. will be cantilevering several inches through the insul., and have to be fiddled to locate solid conc. for anchorage. It all seems a fairly simple forming system, with some insulating value too, but a complicated detailing job to do right, structurally. And, the Arch. and the G.C. may not be all that enthused about following that detailing.

 

[XR250]

... also if you use Simpson nifty ICF ledger system, read the fine print. It is not designed to take out-of-plane loads so those must be managed separately (unless things have changed).

 

[SRO]

phamENG / JStructsteel;
Thank you both for the feed back on the fire cuts.

dhengr;
Actually the 22k load will be on an interior traditionally formed wall. The max Pu on an ICF wall is 10.4k. The walls will be a 8" thick (12" ICF) flat walled system, however it will be at the ridge 12' above where the 2nd floor framing braces the wall. I designed it as an 8"x12" reinforced concrete column. Does that approach concern you? I'm comfortable with the math, but this is my first project with ICFs, so I'm not familiar with any of the real world limitations. I am using the Simpson ICFVL ledger connector system. Although that might change after reading XR250's post, so thank you for the heads up about the anchor bolts. If I do change to bolts I'll be sure to have the insulation removed so the bolt goes directly into the concrete w/ no insulation between the ledger & concrete.

XR250;
I didn't see anything in the Simpson 2019-2020 catalog about that, but thank you for the heads up. When looking at the product after reading your comment, it doesn't seem that there is any substantial connection that would resist out-of-plane shear. I will definitely look into this further. Thanks!!

 

[SRO]

XR250;
I just got off the phone with Simpson and you are correct. There is no out-of-plane capacity with the ICFVL Ledger connection system. I wish they made that a little more obvious. Thanks for saving me the cost of a defense lawyer. I owe you a beer.

 

[jayrod12]

To work around the lack of lateral with the nifty ICF-VL system, I've trasnitioned to having the contractor cut out 10" x 10" sections of foam at the anchor locations andhave them pour the concrete to outside face of foam. Fasten the ledger the old fashioned way.

 

[SRO]

jayrod12;
Thanks. I think that's what I'll do.