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Old 01-23-2013, 09:06 PM   #1
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Seismic retrofit


I live in earthquake country and I plan to do a seismic retrofit. There are some excellent online resources that discuss seismic retrofitting, but this one really stands out:
http://www.bayarearetrofit.com/

The first attached picture shows a hole I cut in my subfloor so I could get a good look at the foundation (there is no access to the crawl space, and even if there was, there's no room to crawl). You can see that the foundation is massively thick (like 24"). The good news is that there are anchor bolts, as can be seen in the second photo. The bad news is that there is no nut on either anchor bolt (I could only see 2 bolts), the bolts seem to be set too close to the outside edge (within about 1.5"), and even if they were done right, there are not quite enough of them (by my calculation).

I've studied the situation and I think I've got a fairly straightforward cases. Although we're in a hilly area, the foundation is flat (not stepped) and there's no cripple wall. So, the most important things are to the be sure that the mud sill is attached to the foundation, and that the joists are firmly attached to the mud sill. The website cited above gives formulas for calculating the number of bolts needed and such. So, I think I've got a good handle on all of that.

This "UFP" foundation plate seems to be popular for retrofits:
http://www.strongtie.com/products/connectors/ufp.asp
And the "FAP" model also seems to get used a lot:
http://www.strongtie.com/products/co...ap-fja-fsa.asp

However, due to the thickness of the foundation, neither of these plates can be attached from the inside in my case. But, it would be possible to attach either along the exterior (although the UFP would look odd, so I'd go with the FAP in that case). I can't see any possible reason why this would reduce their effectiveness. So, does anybody happen to know whether it is OK to attach these along the outside of the foundation? Thanks.
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Seismic retrofit-p1230001.jpg   Seismic retrofit-p1230006.jpg  

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Old 01-25-2013, 10:36 AM   #2
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Seismic retrofit


One correction... The foundation is 18" wide at the top, not 24".

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Old 01-25-2013, 11:38 AM   #3
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Seismic retrofit


Yes, as long as the exterior of the foundation is flush with the sill plate, the plates can be installed on the outside. You may want to get hot dipped galvanized plates and bolts since they will be exposed to weather.
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Old 01-25-2013, 01:01 PM   #4
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Seismic retrofit


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Originally Posted by handyman923 View Post
Yes, as long as the exterior of the foundation is flush with the sill plate, the plates can be installed on the outside. You may want to get hot dipped galvanized plates and bolts since they will be exposed to weather.
I just called Simpson, and they say that the FAP is not intended to be installed outside, due to moisture issues (in spite of it being galvanized). They also told me that they've only got the UFP10 and FAP, that I mentioned in my previous post. I don't see many options here, other than the FAP on the outside, or adding more bolts to the existing sill plate.

Perhaps another possible option might be the technique shown in this video:

http://www.youtube.com/watch?feature...&v=tg5pfL5eDf8

(see the 5:50 mark). However, I believe that is only applicable in cases where the joists are parallel to the foundation---otherwise, you risk getting the dreaded "cross grain bending"; see the 3:30 mark of this video for a brief mention:



Anyways, if anybody has any thoughts, let me know. Thanks.
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Old 01-25-2013, 01:30 PM   #5
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Seismic retrofit


Or you could do like I did....drill holes, drop in all thread rods and use epoxy to hold them in.

Click on the link in my signature (2-Story Addition) and you will see some of the retrofits I did. My house had only 3 anchor bolts per side....and in one spot I'm using the UFP anchor.
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Old 01-25-2013, 04:15 PM   #6
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Seismic retrofit


If you are willing to drill some holes in the plywood floor, you may be able to install anchor bolts from above.

I did this once before. I drilled a 1.5" diameter hole in the floor right next to the wall sole plate (a 2x4 in my case). Then I used an 18" long masonry bit to drill a 5/8" diameter hole thru the lower sill plate (a 2x6 in my case) and into the stem wall/foundation (all standing in the the room above). I used an impact wrench (with a 12" extension) to drive 5/8" Simpson Titen HD bolts to attach this sill plate to the foundation. In my case, I was replacing the flooring, so the 1.5" holes in the plywood were not an issue.
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Old 01-27-2013, 10:12 AM   #7
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Quote:
Originally Posted by ddawg16 View Post
Or you could do like I did....drill holes, drop in all thread rods and use epoxy to hold them in.

Click on the link in my signature (2-Story Addition) and you will see some of the retrofits I did. My house had only 3 anchor bolts per side....and in one spot I'm using the UFP anchor.

Yes, drilling holes in the existing mudsill and epoxying in threaded rods is an option. However, access is difficult, so that's why I'm hesitating to do so. I'd mush rather drill somewhere closer to the middle of that 18" wide foundation, since that's a much easier angle to deal with. But, it's looking like that's not going to be an option.

Btw, that's a really, really nice thread on your 2-story addition. Sometimes, I wish I could start over from scratch and do everything right from the start, instead of trying to patch up all of the things that the builder(s) messed up...
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Old 01-27-2013, 10:18 AM   #8
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Seismic retrofit


Quote:
Originally Posted by handyman923 View Post
If you are willing to drill some holes in the plywood floor, you may be able to install anchor bolts from above.

I did this once before. I drilled a 1.5" diameter hole in the floor right next to the wall sole plate (a 2x4 in my case). Then I used an 18" long masonry bit to drill a 5/8" diameter hole thru the lower sill plate (a 2x6 in my case) and into the stem wall/foundation (all standing in the the room above). I used an impact wrench (with a 12" extension) to drive 5/8" Simpson Titen HD bolts to attach this sill plate to the foundation. In my case, I was replacing the flooring, so the 1.5" holes in the plywood were not an issue.
That's an interesting thought---something I'd not considered. About half of the floor space is covered in vinyl that I plan to replace, so that's no problem. The other half is knotty pine, and I might be able to remove small plugs of that, which could be replaced without it being too noticeable. That would sure beat ripping out big chunks of subfloor.
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Old 02-06-2013, 07:57 PM   #9
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Seismic retrofit


I've finally made some progress and here are a couple of pictures. The house is on a hillside and this is on the uphill side. It's also the only part of the foundation that has an accessible crawl space. Note that the joists in these pictures are actually for the second floor.

To get to the rest of the foundation, I'm going to have to take up some of the subfloor. That'll probably go kind of slow, but I'll post pictures---if for no other reason than to keep me motivated...
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Seismic retrofit-p2060001.jpg   Seismic retrofit-p2060002.jpg  
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Old 04-07-2013, 06:23 PM   #10
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Seismic retrofit


In addition to the crawl space discussed above, I had 4 rooms where I needed to take up part of the subfloor to get at the foundation. I've completed the first of these 4 rooms and a few pictures are attached---there's a close-up and a not-so-close-up view of both of the foundation areas that I had to deal with in this room. Note that along one wall I put in additional anchor bolts, while the other side was better suited for anchor plates. Of course, there are shear transfer ties on both walls.

Btw, this was the most difficult of the remaining work, so the rest of it shouldn't take too long, once I get motivated to do it. Unfortunately, like a lot of my projects, the closer I get to the finish, the harder I find it is to stay motivated. That's going to be even more true once rockfish season opens in a couple of weeks...
Attached Thumbnails
Seismic retrofit-p1010029.jpg   Seismic retrofit-p1010030.jpg   Seismic retrofit-p1010034.jpg   Seismic retrofit-p1010037.jpg  

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