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Re: Wall loading to exist. slab

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Joe,
 
According to IBC (apparently, this is what you are using), the "minimum depth of footings below the undisturbed ground surface" shall be 12 inches (1805.2).  The values of IBC Table 1804.2 presume that depth, and may be inapplicable to your case of the slab.  UBC is even more explicit about the correlation between the "minimum" values and the depth of footings.
 
The vertical load of 780 plf is not that low for a wall that currently appears not to carry any load (partition).  The currently unloaded slab under that wall will, most probably, settle and crack under such load. 
 
The lateral load of 216 plf is a substantial force that will require plywood sheathing, shear anchors, and, possibly, holdowns.  How are you going to embed those into a 4" slab?
 
I agree with Bill Allen regarding the possible repercussions of that seemingly small job.  Compared to those, pouring a new footing for such wall does not appear to be that big of a problem.   
 
Steve Gordin SE
Irvine CA
 
 
 
----- Original Message -----
From: Joe Grill
Sent: Friday, March 17, 2006 6:50 AM
Subject: RE: Wall loading to exist. slab

It?s vertical, I wasn?t very clear on that.  Also, It is a partition wall that wasn?t intended to be a bearing wall, but if the joists bear on it, it will assume some load, and that is the max load it would assume vertically.  The shear load to the wall is 216 plf and that is a wind load.

Joe

 

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

P.O. Box 3924

Sedona, AZ  86340

PHONE (928) 282-1061

FAX (928) 282-2058

jgrill(--nospam--at)swiaz.com

 

-----Original Message-----
From: Mark E. Deardorff [mailto:mdeardorff(--nospam--at)burkett-wong.com]
Sent: Thursday, March 16, 2006 4:19 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Wall loading to exist. slab

 

Is that 780 plf vertical or horizontal in the plane of the wall?

 

Mark E. Deardorff, Structural Engineer
Burkett & Wong
San Diego, CA


From: Joe Grill [mailto:jgrill(--nospam--at)swiaz.com]
Sent: Thursday, March 16, 2006 10:30 AM
To: seaint
Subject: Wall loading to exist. slab

 

I am working on a small remodel.  There is a wall that has been shown as a partition wall that I would like to use as a shear wall.  The wall is supported on an existing 4? thick slab.  If the wall carries 780 plf I really don?t think that cutting the slab and adding a footing is required.  If I assume a 45 deg. distribution through the slab and add the thick of the wall (3.5?) the resulting soil pressure is only 810 psf almost half of the 1500 psf that is being used on the project.  The exist. slab is in very good condition.  Is there a reason why this just can?t be done?

Thanks,

Joe Grill

 

Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying

P.O. Box 3924

Sedona, AZ  86340

PHONE (928) 282-1061

FAX (928) 282-2058

jgrill(--nospam--at)swiaz.com