Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: plywood diaphragm restrained fdn wall

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The mode of the structural performance of the basement walls greatly depends upon the backfilling process and on the future condition of soil.  If backfilled (preferably, simultaneously on both sides) after the diaphragm is in place, it is initially a restrained wall; otherwise, it's a cantilever wall. 
If soil moisture content will change during a heavy rain, the wall may act as a basement wall anyway. 
With the apparent considerable depth of the basement (12" blocks), the diaphragm will be taking quite a bit of permanent force that is likely to increase during the rains.  Such arrangement is not particularly beneficial for the wood diaphragm that is likely to creep, crack, and distort in the long run.  If the diaphragm is flexible (especially, in time), the walls may start acting as cantilevers anyway...
From the "forensic" - long-term - standpoint, if they are planning carpet flooring, the flexible diaphragm is OK; for rigid flooring (hardwood or stone) it may be a problem due to the aforementioned reasons. 
For a wall, I would use two layers of rebars, and design the footing for a cantilever.  For the diaphragm, I would place a concrete slab (thinnest possible) over plywood to resist the lateral compression.
Steve Gordin SE
Irvine CA
----- Original Message -----
From: Joe Grill
To: seaint
Sent: Wednesday, January 11, 2006 8:44 AM
Subject: plywood diaphragm restrained fdn wall

I am working on a foundation for a residential structure for a co-worker in our office.  I took the opportunity to try to set it up on Risa3D as we are trying to minimize the CMU (here most fdn walls are CMU) thicknesses.  By the way, this morning the local axes display miraculously worked (don?t know what I was doing wrong yesterday).  Due to the depth of the foundation he will probably still have to use 12? CMU and use the floor diaphragm as restraint at the top of the wall. 


If a person assumed a rectangular box basement with the same fill on opposing sides then the diaphragm/floor assembly will be in compression, and in my case about 500 plf to the diaphragm.  The floor joists will be perpendicular to this direction so I will suggest he install some blocking at some spacing to get nailing into the diaphragm.


I guess this is another one of our questions regarding the IRC code.  The IRC would allow this for a 9? high basement wall with no further consideration in the floor diaphragm.  He has 10? walls.  Will the plywood diaphragm take this magnitude of compression?  It seems that historically it will.


Any comments?




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