How Do Residential Basement Walls Stand? 4

[BSVBD]

For years i've been designing restrained basement walls for commercial construction with rebar at 12" oc EW as an example of the typical norm.

So why do residential basement walls not require rebar like commercial structures do? How is this possible?

I've heard a residential contractor say, "We don't do that in residential construction." So how do natural forces know whether or not to act dependent upon building occupancy?

 

[XR250]

I agree with Houseboy as those have been my observations overt the years. I do about 75% residential and it is quite lucrative. I only work on custom houses and additions and do alot of pseudo-forensic work for homeowners. I generally over-design things so I do not have serviceability call backs. My clients are typically happy as the cost is not significantly more and keeps them out of trouble. As far as basement walls go, I typically design for the rebar to be in the center of the cell and detail at the edge. I figure I am pretty safe with that.
Oh, and I do not design with i-joists or floor trusses (thanks to all my forensic work) unless the client begs for them. Most of my clients dislike them and prefer 2x10's and steel beams.

 

[sticksandtriangles]

I do not know if any one here watches "This old house" on PBS, but they just poured probably an 8" thick basement wall about 10' high with 0 rebar in it.
They completely back filled against the wall without have the first floor installed. This is a 10 ft high retaining with 0 vertical rebar and they have the nerve to drive trucks very close to the wall.
I was watching the show in amazement that wall still worked link can be found here.

Episode of the wall being poured:

http://www.pbs.org/video/2365707644/

Episode of the backfill and driving the trucks very close:

http://www.pbs.org/video/2365713348/

 

[msquared48]

It won't work for long... Soon it will be a flat slab.

Mike McCann, PE, SE (WA)

 

[XR250]

I do not know if any one here watches "This old house" on PBS, but they just poured probably an 8" thick basement wall about 10' high with 0 rebar in it.
They completely back filled against the wall without have the first floor installed. This is a 10 ft high retaining with 0 vertical rebar and they have the nerve to drive trucks very close to the wall.

I see that alot in articles from JLC and Fine Homebuilding. Ironically, they are usually written about jobs that occur up north as well. Must be a cultural thing

 

[oldestguy]

I watch the show now and then. Years back another guy with more experience did the MC type job that the Keven O'C. now does. Why and a tool belt amazes me, but that is PBS. Most of the old timers are pretty good at what they do (I think), but seldom do I see any need for engineering, as with plumbing fixtures, etc. Yes, it's amazing that PBS didn't have a failure to video yet.

 

[HouseBoy]

s and t and ms48,

Looks like 10 inch walls and 9 feet tall to me (counting lines on forms and guessing it's a 2x6 sill plate with about 4 inches of concrete showing).
I saw a couple of bars in there. Maybe they put 2 bars top, middle and bottom. Not enough to qualify as "reinforced concrete" but still, it is something. Still... looks like they would have just stopped the top bars in (along with "wet sticking" the ABs).

Looks like longest walls are 24 feet between offsets (counting forms and guessing based on AB spacing). We usually don't see problems until we get over 30 ft long and 40 ft and 5 ft walls are def bad actors.

Rock "ledge" at the site seems like it will help prevent much affect from the trucks onto the basement walls.

I'd prefer deeper gravel backfill and rigid pipe instead of corrugated though.

Just some thoughts

 

[DaveAtkins]

I actually played around with checking an 8' high, 8" thick, unreinforced concrete wall several years back, and was able to justify it as follows:
* Use ACTIVE, not AT REST soil pressure (I know, it doesn't fit our usual assumptions, but even the commercial IBC allows this for short basement walls).
* Use 7.5 times the square root of f'c for the modulus of rupture of concrete. And don't use the 0.6 phi factor for plain concrete design.

My point is I totally agree with TLHS--our conservative assumptions make it look like an unreinforced concrete basement wall won't work.

DaveAtkins