20 high basement wall and diaphragm

huangyhg

20' high basement wall and diaphragm
basement walls of 20鈥?in height
residential
ibc 2006 north carolina
paragraph 1610.1 鈥淏asement walls and other wall in which horizontal movement is restricted at the top shall be designed for at rest pressure鈥?
exception basement nor more than 8鈥?below grade with flexible floor
similar wording in previous code
table 1601.1  for most sandy types of backfill has an at rest pressure of 60 psf
for reinforced masonry with 12鈥?cmu that puts a limit at about 12鈥?with 11鈥?of backfill.
if you go to concrete then the wall  is possible but the resultant at the top is app 2100#/ft.
with a typical 戮鈥?plywood floor as a diaphragm the plywood is overloaded.
any ideas on how you have solved such a situation
design the wall as cantilevered, use the active pressure and make sure the wall is backfilled before the diaphragm is put in place.  
given that, i would still design the diaphragm to take some load from the wall for some possible surcharge or soil saturation after the diaphragm is in place.
design the wall as if it were fixed at the bottom and both sides and free at the top (thicker wall and bigger footing).  almost like designing cantilevered retaining wall but not as strong since you have geometry of the house helping you a lot.  i use pca concrete tank design table to design the wall.  it is mostly depend on the length of the wall.  btw, are you building a basketball court in the basement or something?
structuraleit, i must disagree with you.  i think you must use at rest pressure.  if you design it as cantilever, it is going to be huge. i think you have to design it like a concrete tank.  
there is going to be another floor at the 10' level but if you count on that as a support you still have too high of a stress for a typical residential diaphragm.
i have suggested a concrete floor at either the 10' level or the 20' level but none of my clients ever want to pay for that.
apparently they find someone that comes up with a design because i never hear from them again and i never check out what someone else may have designed.  i  have seen cmu wall that high and are standing but i wouln't do it.
what's the wall length?  you might be able to design it for two-way bending like coengineer is suggesting.
bylar, is it going to be a walk out basement also or there is going to be a 10' basement wall on the other side of the house?  watch out for slope stability.  you might design the house correctly but the house wont stand if the whole hill slides.  if you have a walk out basement you definately need to work very close w/ the geotech. eng.  
just design it like a tank with counterforts at long span and your footing and wall thickness wont be too crazy.
i will concur with coengineer on the at-rest pressure and not designing as cantilever to cut down on sizes, but i would still backfill before diaphragm is in place to avoid taking that load into the diaphragm.
bylar-
is the basement 20' high or are you using cmu for the entire height of the house?  the op seemed like the basement had a 20' high ceiling, but your last post seems like it is a 10' (or less for framing) basement ceiling and the cmu continues to the second floor. which one is correct?
this topic was just discussed at length on another post.
go here for the thread:
as i say in the post i believe masonry wall is out of the question.
yes it is a walk out basement with both side wall masnry or concrete.
i have already considered the sliding effect.
to me the only solution is have a concrete floor at either the 10' or the 20' elevation.
i don't believe a retaining wall is practical.
i feel somewhat confident in i analysis of the situation but i have seen it done with simple reinforced masonry and even though the walls are in tact and still standing i do not believe it complys with the chapter 16 that i originaly stated.
i had looked at the sited thread before i even posted mine but the conditons are not th same.
ok, venturing into the dangerous territory of the other thread, lol...
if you consider it to be a cantilevered wall, the big downsides are:
1. the wall (cip concrete for sure) and footing will be huge.  answer: too bad.  it is what it is.  they don't like the other option of installing a concrete diaphragm.
2. the wall will deflect later on and possibly damage your diaphragm or other lfrs elements.
why not bite the bullet and cantilever the wall?  deal with item 2 with detailing.
depending on your situation, the total wall deflection would be 0.8" to 1.0" according to the various crsi cases.  try to figure out how much of this should occur later on, after the diaphragms are installed.  it might not be enough to spit at.  detail your system to handle the deflection.  it might not be that hard to do.
what kind of backfill and drainage system are you planning to use?  i know i'd feel better about it if i had granular backfill going back at an angle, plus a drain at the bottom.  i'd be a lot more scared with clay behind the wall.