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Re: Basement Walls

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Horn:

I did a custom 10,000 sq. ft. home on hill side lot about 10 years ago.
One side of the first floor wall is acting both as a retaining wall and
pin-pin basement wall.  I think this is what I had designed, I specified
the rebars to be placed in the middle of 12" CMU wall with a wider
footing for temporary backfill loading.  Once the first floor diaphragm
was constructed, the wall will then act as pin-pin basement wall. Of
couse, I had also checked the shear-transfer load path from the
retaining soil to the diaphragm and then to the side walls and side
wall's footing.  Also, I remember I check the whole house for sliding
due to the retaining soil because one side is facing the hill side which
has caissons.

As far as apartment buildings in California, typically, we have 4-story
type V on two story Type I concrete basement for parking.  The basement
walls are usually designed as pin-pin basement walls.  However, I always
specify NO BACKFILL until the concrete slab is fully cured.

Tom Chiu, SE
Thomas Engineering


Horn wrote:
> 
> My brother is an Architect and we have been involved in the design of
> several custom homes.  We have an on-going argument about the design of
> basement walls.  He insists that homes the Salt Lake City area
> 
> with basements require only 24" wide footings for basements walls.
> Basically, the walls is pinned-pinned!  I've been able to be involved in
> homes with owners with enough money to not complain too much about the
> cost, and an Architect who responds well to some coaching.
> 
> I live in Illinois now and I've been looking at homes around here
> (most have basements) and they do the same thing.  There's no way these
> walls are evaluated as retaining walls.  I've checked the loads on this type
> of configuration and the shear that has to be dumped into the
> diaphragms is considerable.  The idea of preloading a wood diaphragm with large
> amounts of deadload and then needing additional reserve capacity for
> seismic loads of the structure and additional soil lateral loads is not very
> appealing to me.  I have submitted to considering the retaining wall as
> fixed at the base and pinned at the top in some instances.
> 
> Has anyone else been pressured to not design a basement wall as a
> retaining wall?  If there is anyone who has / does do this, please let me
> know what the justification is.
> 
> Scott Horn
> 
>