6" basement wall
6" basement wall
(OP)
Question. Is it permissible to design a restrained basement wall 6" thick as long as it meets the requirements of rational design per chapter 10? Lateral loads will be the at-rest loads.
ACI 318-08 section 14.5.3.2 limits the thickness of exterior basement (restrained) walls to 7½" thickness when designing by the 14.5 - Empirical Design Method. For a wall designed under 14.4 – Walls designed as compression members, I can find no such limitations.
ACI 318-08 section 14.5.3.2 limits the thickness of exterior basement (restrained) walls to 7½" thickness when designing by the 14.5 - Empirical Design Method. For a wall designed under 14.4 – Walls designed as compression members, I can find no such limitations.






RE: 6" basement wall
RE: 6" basement wall
RE: 6" basement wall
BA
RE: 6" basement wall
RE: 6" basement wall
Hayden, it's typical to see at least 8" thick wall in basements and I normally start my design there. Even if I can make the numbers to calc up to 6" wall, I would not use it for my basement walls. BA mentioned 1 issue with the rebars. A 6" wall would not have a lot of tolerance with regards to the rebar layout + you'll have 3" concrete cover requirement at the retaining side for concrete cast against and permanently exposed to dirt. Then you'll also have the issue of requiring shoring at the top of the wall when the floor joists are not yet in place.
FYI, your calcs show active pressure value that is normally used for unrestrained design. For restrained retaining wall design, active pressure is normally higher, maybe in the 60 psf/ft or more range. Check your soils report.
RE: 6" basement wall
Sorry, not a Noob. I am a registered P.E., S.E. with 18 years in practice. For 7 years I did nothing but precast/prestress design. I just live in the boon-docks now so I don't have a local sounding board.
I agree that the biggest challenge is rebar placement. In a plant cast situation, there is total control of rebar location which is why they have smaller cover requirements. I have designed miles of 4" above grade wall and 6" retaining wall in a precast plant designed under the PCI handbook. This Standard allows things that cannot be done under ACI. In a standard wood form I also use 8" due to concern for rebar placement.
I am looking at ICF and this gives me back the control of the reinforcement location because of the tie system See attached pdf. I make conformation of the bar location a special inspection item. If the horizontal bars are snapped into the correct holders and the vert is between them the bar WILL stay in the correct location.
I am 95% sure this is not a problem but it never hurts to sound out other engineers.
RE: 6" basement wall
With ICFs, the problem is proper vibration (not over vibrated) and placement of the concrete. This is really critical near corners and around/under openings. Unfortunately, the forms are never seen, so the poor placement can go unknown.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: 6" basement wall
I have dealt with these animals a few times over the years and heard many claims. I would stay away from the suppliers that just wave their hands saying their product has been used many times in similar situations when they cannot provide you the documentation to prove it. I've seen that and backed away real fast.
I believe that the code requires 8" walls for two story structures, but there is an exception for TESTED and proven systems.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: 6" basement wall
In one case I recall, the foam face was removed only to find several cold joints in the wall. The contractor was using concrete left over from other pours to fill the wall forms.
Honeycombing or voids in the concrete cannot easily be detected in ICF systems.
BA
RE: 6" basement wall
I will only use a block that has good test data behind it but do not use any of their load tables. All designs are specific to the actual loads and comply with ACI 318-08 rather than their tables.
Msquared48, you mention an 8" requirement but I am unaware of one. Do you know what Standard that would be in. I have seen local jurisdictions that have a standard basement design that is required unless the wall is designed by a registered Professional Engineer. That is the main thing I am looking for. I know that I can get these walls to work from a øMn > Mu basis. I have not found anywhere a Standard says "THOU SHALT NOT BUILT A BASEMENT WALL LESS THAN x INCHES THICK!!
Can anyone think of a minimum thickness provision. As I said, the only mention on thickness that I can find is Empirical design and section 14.2 trumps that. I have designed sandwich composite panels that were 22' tall where 60' roof double tees were bearing on the inner 3½" wythe but that was with prestress so it is a different animal.
RE: 6" basement wall
RE: 6" basement wall
RE: 6" basement wall
Think of this mix as a thick SCC. Internal vibration with a ¾" pencil vibrator in this mix yields pretty dense concrete.
RE: 6" basement wall
I don't think there is anything wrong with your approach.
BA
RE: 6" basement wall
Some of the ICFs suppliers use the ICFs as a part of their sales when they are not making meat trays for Walmart, Sams Club or Costco. Others have exhaustive technical support, specifications, installation guides, test reports and design tables to be used as guides, but a good engineer should be able to see where they are conservative for the uniformed. A good design can be done with the information available for specific applications.
One site I have used frequently is "Reward" ICF (no plug intended) and there are several other very professional brands that are also around.
The good systems were quickly controlled by the more progressive suppliers (real building materials dealers or major concrete suppliers) and the followers just tried to copy as close as possible without enfringing on patents, but tried to make them slightly cheaper to buy into the market late.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: 6" basement wall
IBC 1909.6.1 limits a structural plain concrete basement wall to 7.5" but that's not your situation.
IRC has a lot of prescriptive stuff on ICF walls. Table R404.4(1) takes a 5.5" ICF basement wall up to 10'-0", but you're not bound by this if you use ACI. IRC R404.4 refers ICF design to ACI if not using their tables.
ACI doesn't seem to limit you, so I think you're good with the 4" as crazy as it might seem.
RE: 6" basement wall
The one only project I had (3 years ago and I was only in residential market for 1.5 years) all exterior walls made out of ICF. Not only foundation walls. So you probably pick the exterior wall ICF product, not foundation.
Never, but never question engineer's judgment
RE: 6" basement wall
Have a look at the attachment in my last post.
BA
RE: 6" basement wall
I am planning to start using 4" walls for above grade work as long as I have enough wall to keep the in-plane seismic shear forces to less than 1 square root of f`c. After that I will go up to 6" to avoid the need to kick in the special reinforcement requirements.