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Earthquake retrofits

I checked out the San Leandro site previously. Very good info there. Their PDF on foundation bolting shows foundation plates that are no longer available (as far as I could tell!) Only Whitecap sells those L shaped plates anymore, but they are not as easy not as strong (400 lbs lateral resistance versus 1340) as the UFP plates. UFPs are the way to go where there is no clearance to get a rotary hammer in place to drop an anchor bolt.

Most sites show epoxy and wedge/sleeve anchors as the only solutions to retrofit bolting (ie; there were no bolts set in the concrete when the foundation was built) but they don't mention the Simpson Titen HD bolts, which are much easier, since you just drill a hole (assuming it's a good clean hole) and screw in the bolt. Tapcon also makes a bolt similar to the Titen HD http://www.itwredhead.com/ldt_prod01.asp called the LDT (Large Diameter Tapcon) but I think Simpson did extra load testing on the Titens. I'm sure the Tapcons are just as good, but I'll stick with the titens.

Epoxy bolting means buying epoxy, tips, injector... but it's better for crappier concrete because wedge anchors expand and stress the concrete, but both are "rated" for earthquake bolting.

It's amazing how much you can learn if you are motivated and have internet access! ;)

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Simpson Titen is one of those bolts that has the wedge sleeve already connected? I can't imagine how you'd grab onto the concrete without any sort of wedging action.
 
The Titen HDs just grab the concrete. So a 1/2" bolt means you actually drill a 1/2" hole. The shaft is 1/2", the threads extend out beyond 1/2" and cut into the concrete. The key is that the leading threads cut the concrete, so the hole you drill has to be 1/2" deeper to contain the concrete dust. The Tapcons work the same way. They are approved for use by a bunch of agencies in earthquake retrofit and are the easiest way to do it. Epoxy is expensive and messy but more forgiving if your hole is not a nice round hole. In anycase, I bought 20 of them so my holes had better be nice and round! I plan to practice drilling by drilling into the "ratproofing" concrete on the crawlspace floor where I'm going to sink some footings for my 180 tank supports.

http://www.simpsonanchors.com/catalog/mechanical/titen-hd/

So I guess the threads are the "wedge"

V
 
Ahh ok I get it. Seems like you could potentially run into issues though if the hole isn't exactly 1/2" wide, I know using a hammer drill it is very easy to "round out" a hole and have it a bit larger than the bit that drilled it. At least with the expanding locks they can compensate for a not so perfect hole, hopefully your foundation wall is thick enough that pushing out doesn't make a huge difference. I agree with epoxy, PITA to work with, hole needs to be blown out and clean.

So you either use bolts, or you use the UF Plates? Could get expensive as all hell to retro a house :D

I was looking into the sheer wall too, couldn't find any information to how thick the plywood needs to be, were you able to find anything out? Seems you don't need to sheet your walls (in the case of me an exposed basement/garage) completely, but in certain key places you should.
 
http://www.strongtie.com/ftp/fliers/f-plans07.pdf

That's the Simpson guide. It mentioned 1/2" Sheathing plywood. I guess it's specific for this type of task versus the "utility grade" or "shop grade" or the nice stuff.

The UFP is for places where you can't drill a hole for the anchor bolt from above through the mudsill. If you have cripple walls, most likely you can use an anchor (for like $4 or something). Half my house does not have cripple walls (good so I don't need shear panels) but I can't get a drill into the space to drill down a hole for the anchor, so I have to use the expensive UFP (Universal Foundation Plate) hardware and connect the mudsill from the side. They are actually stronger than some anchor bolts, but that's because each plate uses TWO anchor bolts sunk in sideways, and then are screwed with 5 special screws to the side of the mudsill.

Anchor bolts are obviously cheaper since the UFP uses two anchors anyways, but obviously, you gotta get them into place.
It seems like a few years ago, Simpson dropped all other anchor plates in favour of the UFP and many retrofitters say that's a good thing since they are stronger and easier to install (all screwing is from the side, you don't have to sink nails from above) and are more "Universal" due to their S shape.

My house was built in 1939, so it's got a lot of upgrading for earthquake. Though it is made quite sturdy from what I've seen. There was also some half-hearted retrofit attempt done, I think right after Loma Prieta, but it's more of a hinderance. The shear walls that are wallpapered over are 1/4" as far as I can tell. And I can't tell if anchor bolts were installed since there are no holes in it. So the previous attempt actually means that I have to remove it and "do it right" according to more modern code, but also that I can slack on it for a bit since it's something, versus nothing.

Read that PDF and the San Leandro site. Also check out bayarearetrofit.com, they have a forum (which you can't actual contribute to since you have to register and they don't actually allow you to register!) but if you have a question, you can email the site owner and he'll actually respond (in very few words, but to the point).

V


V
 
Gresham, in my case I should have said "unmotivated!"

Oh yeah, the San Leandro site is cool because apparently San Leandro has a Tool Lending Library! How cool is that?! Need a rotary hammer? OK, go check it out. Need some drills? Wow! Stupid San Mateo, what, I don't pay enough property tax? Bah Humbug!

V
 
Saw your comments and had some info to add:

Calculating the shear force is very difficult without knowing much about a home. I home with a tile roof will produce much larger shear force then a home with a shingle roof. Also what you put in your home has an effect. You need to consider the "dead load" and the "live load". Also the shape of a house and how the structural elements are oriented makes a big difference. If you wanted to read up on trying to figure that out, look for an engineering book about "statics" That is the first area of structural engineering you learn in school.

The second item was on the plywood. Typically 1/2 inch is used, but it needs to be structural grade plywood. Some of the lower grade plywoods have inner cores that are not very strong. Luckily most of the stuff at HD is for the builder quickly picking up an item they need and their limited inventory space causes them to normally stock the structural grades of plywood.

Good luck with your retrofit. It is hard work.
 
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