Masonry Crawl Space Wall - Seismic Class "D"

[krus1972]

I have a 4'-0" deep Masonry Crawl space wall, below grade, that is on top of a continuous footing. Throughout its entire length, the masonry wall supports the shear wall from the building above. We are in Seismic Class "D", so the building shear walls do impose the seismic shear load into the top of the masonry wall.

According to Table CC-7.3.2-1 of the TMS 402-13/ACI 530-13/ASCE 5-13 page C-83 a "Special Reinforced Masonry Shear Wall" needs to be used in Seismic CLass "D".

In section 7.3.26 (a) and (b), page C-85, the maximum spacing of horizontal and vertical reinforcing should be one-third the height which is 16" in this case.

My question is, if this wall were only 12" deep, do we need to place the horizontal & vertical reinforcement at 4" on center? This reinforcement requirement seems to be an overkill as the wall gets shorter....? The CMU units are only 8" deep...

Does this basement wall really need to be classified as a "Special Reinforced Masonry Shear Wall" or can it be classified as something different since it is a crawlspace wall and not a building shear wall.

Any guidance and code reference would be well appreciated.

 

[mmarlow]

Krus,

Horizontal reinforcement every 16" doesn't sound too excessive to me. Vertical reinforcement every 16" sounds even less excessive. I have found myself in cases where I called for every cell to be grouted, and had a number 4 for out of plane bending. However, these situations were for taller exterior walls subject to high wind loads.

In regards to the 12" wall hypothetical situation. If this is a project in design, I would think the engineer would want to avoid this situation for multiple reasons..
1) Convenience of sticking to applicable code
2) Construct-ability
3) ease of design using the same material for the entire shear wall.


I could see an 8" masonry collector being used in combination with a concrete wall. However, I feel your hypothetical situation is unrealistic and rarely, if ever, will need to be addressed. In your particular situation, I think its reasonable to go forward with what the code says. Assuming you have a concrete shear wall on top of the masonry, tightly spaced vertical rebar will have to be embed into the shear wall to transverse the base shear anyways. Also, out of plane bending against to resist seismic on retained soil will stress vertical bars.


Keep in mind, I do not design in SDC D areas. Sorry I couldn't refer you to anyting in the Code, this is just my take.

-MMARLOW EIT

 

[msquared48]

Krus1972...

Have you checked the commentary?

Mike McCann, PE, SE (WA)