Earthquake Retrofits in a Corner Basement Room

[RWebb]

I wanted to ask about strengthening a corner room in my house to retrofit it for earthquakes. They are telling us that earthquakes in Orygun will be less common than in Calif. but more severe. This house was built here in 1963, so I assume it met code at that time…

Here is the situation: This house has a main story on top, and a daylight basement that is dug into the hill on the East side – this room is in the SE corner. I pulled out the crummy acoustic tile ceiling to insulate it and while it is opened up, I am wondering what I easily do to retrofit it for earthquakes. I already used Simpson Base Plates to tie the mudsill on top of the concrete walls down better.

The east side of this room consists of an 8 ft. tall concrete wall, which extends all the way across the rest of the east side of the house, then turns a corner and goes out westward to form most of the wall for other rooms on the north side. On the south side, this of this 8 ft. tall concrete wall extends 2 feet west, and then it steps down to a 4 ft. tall concrete stem wall. Two windows sit on top of that 4 ft. tall concrete stem wall in this room, and then at some point further west, this wall on the south side of the house becomes just a low foundation. A bathroom and kitchenette make up that part of the south side of the interior (not shown). Each of the two windows are about 28” ht. and 4 feet long, with a bit of sheetrock on top of them to the ceiling.

On the north side of this room, the wall is just 2x4 studs, with what looks like doubled 2x4’s forming a top plate. Joists for the main floor are made of 2x10’s, and run N-S from the exterior wall with across and beyond the interior stud wall. I can see that they run at least a couple of feet past that wall, but I’m not sure if they run all the way across the stair well on the other side of the interior stud wall.






So, this room is 13 feet N-S and 11 feet E-W, with two exterior walls – one that is the 8 ft. tall concrete wall (E. side) and that 4 ft. tall concrete stem wall with the windows on top of that on the S. side. The other two walls are interior 2x4 studs. On the N. side is where that stairwell goes up to the main floor. I am thinking that I can maybe just cut some holes in the sheetrock on that interior wall and then use Simpson ties to attach the studs to the stairwell – this would turn the stairwell boards into a diagonal brace. That way I would not have to rip out all the sheetrock and use plywood to turn it into a shear wall. I can also use some sort of metal plates to tie the beams onto that stud wall, say the Simpson H10’s (which are like hurricane ties, but much stronger. What I don’t understand is whether the interior wall even needs to be a shear wall. Nor whether my idea makes it strong enough. I also don’t know how well the bottom of this stud wall is attached to the concrete foundation (nor how deep that concrete is).

For the exterior wall on the S. side, I would need to figure out how to deal with those windows, since they interrupt the load path for the wall. Any ideas on that?
I could tear all the sheet rock off on the interior and then see if I can’t bolt various studs together or something. (The windows cannot be removed, as code requires them for a fire exit – but if I had to, I might be able to remove one of them). There is only another 1 foot of wall to the W. of the windows. At that point, you hit an interior dividing wall and then the bathroom, then the kitchenette, which cannot be messed with.

Here is the corner of the exterior wall:




Diagram of Exterior Wall:
(gray is the 4 ft. tall concrete stem wall)





Diagram of what I think the interior wall looks like:

[RWebb]

So is there anything I can do to strengthen the exterior wall for earthquakes (from the inside)? And, really, I am talking about a segment of the entire wall on that side of the house.

[looneybin]

There is not much you can do to retrofit the concrete walls without costing major $$$
if you have a quake that strong, those conc walls will be the least of your concerns.

You can add plywood shear panels on the stud walls, but the window perforations don't do allow any shear value in that area anyway

[ODDJOB UNO]

i think yer bucks would be better served buying WATER WINGS/LIFE RAFTS/SNORKELS for when the cascadia fault ruptures and the SURFS WAY UP!


just saying, WTF do i know about tsunamis?