3-Story Hotel with Basement - Basement Shear Walls?

[cuels]

I should probably have encountered this before, but unfortunately I haven't, or maybe I haven't thought hard enough about it. I am designing a 3-story wood framed hotel with a basement, which is going to have interior shear walls. In my mind, I should carry the shear from all stories down to the basement slab and into a footing, transferring the shear through anchor bolts into the footing. However, I don't know that this is common to shear an interior basement wall. I have heard that these can be transferred to the floor diaphragm and then magically it transfers into the soil providing passive resistance. This doesn't make sense when I have a 12 kip shear load transferring into the floor diaphragm and down to an anchor bolt and into the soil??? Is it common to sheet basement walls, in a building such as this, to transfer shear to the footing, and in that case, even a crawl space knee wall? Or, is there another system that is being developed through the foundation wall and floor diaphragm that transfers the shear to the soil around the perimeter of the 1st floor diaphragm?

 

[msquared48]

I take it that the interior shear walls are wood and the ceiling of the basement is wood framed.

You may be able to distribute the shear at the first floor through the wood diaphragm, but you still have to take the hold down uplift forces to the foundation, either by beaming it out at the floor level to the exterior walls, or through the floor structure to columns and footings below.

It really depends on the size and shape of the structure. Personally, with all wood framing except for the bottom story exterior walls, I would take the shear from the interior basement walls to the shear walls in the basement if they align in any fashion whatsoever. If you are dealing with parking underneath though, you may want to reconsider here and consider a PT podium slab, not only for structure, but also for fire.

Mike McCann
MMC Engineering

 

[cuels]

So, it is not uncommon to sheath the walls in the basement to transfer the shear? I have the walls in the basement that line up with my shear walls above, but I am not completely familiar with what is common in these cases, so I have to ask.

Is it common to take a 12 kip load into a wood diaphragm? It seems like it would be be a lot for the diaphragm to carry if you have a typical hotel (length > ~2 x width) and you try to carry that to an exterior footing. Somewhere there would have to be an interior shear wall into the crawl space or basement to a footing to fix the diaphragm and reduce the diaphragm L/W ratio...right?

BTW, there is not parking underneath. Just maintenance rooms and storage.

So, the reason we neglect the shear tributary to the 1st floor diaphragm is because it distributes to the soil along the diaphragm. That is, through the rim joist nailing, to the sill plate, through the anchor bolts, to the foundation, semi-cantilevered into the passive resistance of the soil?

 

[msquared48]

On your last question, yes, if the diaphragm and connections can take the load. You have to provide a diaphragm chord with rebar, or whatever, in or at the concrete wall to develop the diaphragm, too, if you do just want to use the diaphragm.

Mike McCann
MMC Engineering

 

[jayrod12]

If I'm understanding your basement correctly you're framing it out of wood?

If that's the case then your pwf foundation walls will need to be checked as shear walls. All of our pwf foundation walls are sheeted. and if you're putting all of the shear into them they may need sheathing on both sides.

We design lots of 3 storey wood framed condos and hotels however we always have a concrete basement and usually a concrete main floor (It's generally parking below the main floor so the concrete is there to provide the 2hr fire rating). Then we just provide adequate tie-downs of the shear walls to the foundation elements (i.e. concrete walls, and columns)