Wood joist to brick wall connection force 1

[milkshakelake]

When tying a joist to old masonry, what force do I need to design it for? Would it simply be the controlling value of seismic and wind components & cladding force of the floor applied uniformly? I have a feeling that this is engineering judgment, but a reference would be nice, if it exists. Also, is it typically every 3rd joist or 4th joist?

 

[jayrod12]

With your detail, I'd anticipate it's every joist since it's a lag screw into end-grain (which is a horrible detail if you ask me).

I would prefer to do a threaded rod to a simpson strong-tie DTT2z connector to the face of the joist. Far more capacity, and then you could space out the connections further to whatever distance the wall can span/whatever load the connection can take.

 

[milkshakelake]

@jayrod12 For a connection to the side of a joist, wouldn't it be difficult to get into the cavity between joists to make the connection? Some existing bricks would have to be taken out and replaced.

A connection into end grain isn't recommended, but I think it's just a reduction of 25% capacity per NDS 2018:
12.2.1.3 Where lag screws are loaded in withdrawal from end grain, reference withdrawal design values, W, shall be multiplied by the end grain factor, Ceg = 0.75.

 

[bookowski]

Looks like you're doing dm drawings in nyc. Steal a few dm drawings by others and you'll see what's typical. There are only a few details that get copied over and over for this, near zero engineering typically.

The adjacent building joist will be held back at least 1 wythe, so you're removing some brick no matter what. That end will also be fire cut, so you'll be hitting the joist end at an angle (not worrying about capacity with that statement, just constructability of your detail). Going to the side of the joist is not atypical in these situations but you are correct that it requires opening more of the wall. 50% of the time your client gets permission to enter the adjacent property and do it from inside (and pay for repairs). When that can't be done you can open a larger cavity. If you don't want to or can't do that then going into the end grain is also done. I have seen it done with "sammy" type connections, where it's got a lag with a threaded coupler on the end. It gets screwed in, you thread a rod on, you brick up around that rod, and then put your plate and nut on. Nobody checks these for loads in the condition you're looking at, I usually see something around "5'-0" o.c. max" and if you're smart you locate their stairs (assuming that they are on the wall you're working on) and know that there's a trimmer on each end and nothing between. If the wall seems particularly distressed you may want to consider more frequent anchors or using continous channels between anchors.

 

[bookowski]

Here you go, see attached. The end grain one does not seem very robust but i've never heard of a problem with it. I assume that you're going back up with a new building so in real life wind load = 0 except for a bit of time during construction.

 

[milkshakelake]

@bookowski Very astute observation, I am indeed doing demolition drawings in NYC. Maybe we've bumped heads before, who knows. It's a small world.

Thanks so much for the explanation! It's been really helpful and I have a much better idea now. The details you provided are great, I'm going to adapt it a bit. I can't express how helpful you are, thanks a million kips.

 

[bones206]

I noticed in your details it calls for some version of brick coating/waterproofing. Is there a coating system that has performed well in NYC for these applications? I always thought the conventional wisdom is that waterproofing or sealing bricks could lead to problems, if the coating prevents the bricks from drying out. I imagine the trick is using a coating that sheds water but breathes vapor.

 

[milkshakelake]

@bones206 I haven't had any issues when weatherproofing brick with Karnak 19 or Thoroseal, and it's accepted by the city building department. Some kind of weatherproofing is required by code, with a minimum specified thickness. I kind of disagree with it, because repointing and filling any gaps with mortar is a good solution. Most brick is exposed anyway.

 

[bones206]

The datasheet for Thoroseal indicates that it's breathable, so sounds like a good product for sealing masonry. The Karnak 19 product sounds very heavy duty and not breathable at all, so less sure about that one.

Thanks for sharing. I'm getting more and more projects with older masonry construction, so I've been lurking in these types of posts and trying to learn as much as I can from more experienced practitioners.

 

[milkshakelake]

@bones206 In that case, another product to add to your list is Tremco Commercial Sealants and Waterproofing. I haven't gotten around to researching them yet and setting up a sales meeting since the coatings I specify are generally fine, but I'll do it if I run into issues. I've heard good things about their technical support. If I end up contacting them one day, I'll come back to post the results here.

I used MasterSeal NP 1 earlier this year on one project and it worked well, and was accepted by the building department with a lot of eyes on that particular project. I can't attest to its long term performance, and it doesn't seam like it's breathable. It also needs good surface preparation and cleaning, otherwise there will be pitting. The contractor had to apply a second pass because of the pitting, but they pushed for it in the first place, so they deserved that.

 

[bones206]

Thanks for indulging my tangential question. Brick coating must vary with local customs, because I never see it anywhere in my city. And we have a ton of old brick.