Wooden shearwall on foundation 1

[Simlac450]

Hi Guys,

I need your input on something, I'm currently working on a warehouse, the foundation above ground his 8'6" high, and the exterior wooden walls will act as shear walls (we designed them to do so), there is no floor to laterally support the top of the foundation. So my question is since my foundation is quite high should I design it so it can carry the shear base of the whole structure or partial shear base? Or you guys would have just designed it for gravity loads ?

tkss

 

[DoubleStud]

It sounds like a big building. I would design the wall like a cantilever wall with linear horizonal load on top of the wall from the wind..

 

[Simlac450]

@DoubleStud, yeah I agree, it was in my plan, my concern is more about the seismic load if I should only design it as cantilever wall or should I also take into account the seismic loads.

 

[Greenalleycat]

I don't understand what you mean by "partial shear base" vs "shear base of the whole structure"
You should design it for the loads that actually make sense
This looks to be single storey so I assume your timber shear walls are there primarily to brace the roof?
In which case you are tracking your roof loads, timber shear wall weight, and 8'6" concrete wall weight down to ground (assuming seismic loads?)
Otherwise you are designing for the appropriate proportions of wind loading on the tributary elements - there is not enough info here to fully understand the load path here to advise more on that

The obvious trick with this system is the consideration for how it performs as soon as you add in-plane and out-of-plane loads concurrently
For seismic, this would occur when considering 100% + 30% load cases (assuming your codes work like ours) or for wind would occur when you get a wind diagonally onto a corner of the building (in-plane push and suction along the side of the building)
Now your concrete foundation wall has to cantilever out-of-plane whilst taking in-plane loads, so make sure you design the reinforcement for this
Your connection detail at the floor will also become critical for that case

 

[Simlac450]

@Greenalleycat, tks for your answer, you are describing the procedure to find the lateral load which I already have, sorry if my question wasn't clear, I’m concerned about how to deal with the foundation according to the seismic loads. What I meant by partial shear base is at the moment of computing my shear base, should I use only the height of the foundation or the height of the whole building since the wooden shear walls are attached to the foundation.

 

[Greenalleycat]

Draw a freebody of the situation and the answer should be obvious.
The total overturning moment exists so you cannot simply ignore it
However there is a clear critical interface between the timber shear wall and concrete foundation wall
I would conceptualise the loads at this interface as being a distributed shear along the wall from the timber shearwall with a series of uplift and compression loads at each ends of the wall
This maintains continuity of your moment demands on the shear walls down into the footing, which will then experience greater base moment as you consider 8'6" x the shear demand + self weight of wall x height to centroid of wall
This will give you your design demand at the base of the footing

Possibly your distribution of shear walls will be such that just taking a total overturning moment at the base of the foundation is fine without decomposing the shear wall loads into uplift/compression loads
This will lose some accuracy (but probably not a meaningful amount) at the benefit of saving computational headaches

P.s - don't forget to consider the bi-directional loading cases on your wall..!

 

[jerseyshore]

Simlac, I think you need to be a bit more clear with your question. I can't tell if you're asking how to actually calculate the seismic loads or if you wondering where/ how to apply the seismic loads (or something else entirely).