Uplift in shear wall is too high
Uplift in shear wall is too high
(OP)
Hello everyone,
One of my colleague is designing a 4 story wood building and having some trouble with the design of the hold down. The shear wall are parallel to the joist, so they don't support any dead load. The uplift at the base of the building for the smaller wall is 45000 lbs, we can't seem to find any hold down with a good enough capacity to resist that kind of uplift.
So... Does my load make no sense? Is there something I am missing possibly?
(Sorry for my bad english, it's not my first language).
Thanks for helping,
One of my colleague is designing a 4 story wood building and having some trouble with the design of the hold down. The shear wall are parallel to the joist, so they don't support any dead load. The uplift at the base of the building for the smaller wall is 45000 lbs, we can't seem to find any hold down with a good enough capacity to resist that kind of uplift.
So... Does my load make no sense? Is there something I am missing possibly?
(Sorry for my bad english, it's not my first language).
Thanks for helping,






RE: Uplift in shear wall is too high
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Uplift in shear wall is too high
Can you tell me if my seismic load is out of proportion? I got 461 kips for a 4 stories building of 12000 ft^2.
Thanks for the answer :)
RE: Uplift in shear wall is too high
3 floors @ 180K ea = 540k (15 psf dl)
Total DL = 660k
Base shear = About 0.15 X 660 = 99 K
Your base shear is way too high.
Mike McCann, PE, SE (WA)
RE: Uplift in shear wall is too high
The national building code won't allow me to use such smalls loads.
I also have to consider 25% of the snow load and 50% of the live load.
We also have the worst soil category for this, obviously.
Anyway, we decided to use steel brace in the worst direction, since we already had some steel columns.
Thanks for you answers.
RE: Uplift in shear wall is too high
I'd review the loading you used again, and shearwal layout. You likely want to use the shrinkage compebsating devices for your holddowbs. These can take some nasty uplift loads but Anchorage of the device will be problematic if your loads are too high.
Side note SDS is nearly 2 in some areas by me!
RE: Uplift in shear wall is too high
Based on what you said, I would still use 15 psf DL for the roof unless you are using concrete tile, where I would use 25 psf.
However, I would use 15 (wood framing) + 20 (conc)= 35 psf for the floors.
You should probably add 5 psf for the interior and exterior walls too to be safe.
Are you in Seismic ... C, D, E...? which one?
Even though there is little load to the walls, there is still some dead load at 10 psf minimum to lower the overturning a little, plus probably at least a couple of feet at each floor.
Sounds like your code is far more restrictive with having to throw in 50% of the floor live load. We do not have to do that unless it exceeds 100 psf.
I think you will need more walls as Kootk said, or some transfer beams either above or below the shear walls to lower the holddown forces.
Mike McCann, PE, SE (WA)
RE: Uplift in shear wall is too high
Also, after studying the code, I don't think I need to consider 50% of the live load, it is only for the load combination.
RE: Uplift in shear wall is too high
Mike McCann, PE, SE (WA)
RE: Uplift in shear wall is too high
EIT
www.HowToEngineer.com
RE: Uplift in shear wall is too high
RE: Uplift in shear wall is too high
RE: Uplift in shear wall is too high
RE: Uplift in shear wall is too high
RE: Uplift in shear wall is too high
Mike McCann, PE, SE (WA)
RE: Uplift in shear wall is too high
EIT
www.HowToEngineer.com
RE: Uplift in shear wall is too high
The bigger issue is with taller wood structures shrinkage becomes a more critical component and the shrinkage of the wood can cause the drift to be excessive if a shrinkage compensating device is not used.