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RE: Sec 1815 UBC (slabs subject to expansive soils)

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I am curious about standard practice among engineers using this list. UBC 1803 (1994) states "Foundations for structures resting on soils with an expansion index greater than 20 ... shall require special design consideration." UBC 1804.4 (1994) further states "When expansive soils are present, the building official may require that special provisions be made in the foundation design and construction to safeguard against damage due to this expansiveness."
 
Do you interpret this that if the expansion index is greater than 20, the the provisions of Division III (1815 [conventionally reinforced] and 1816 [post tensioned]) MUST be followed, regardless of you personal desires, and if the building official requires, they must be followed even if the EI is less than 20? Or does "special design consideration" not REQUIRE following 1815 and 1816? Are other design methods outside of 1815 and 1816 acceptable?
 
How do you actually operate your practice in design of slabs on expansive clay? What design methods do you use?

Eric Green, PE

-----Original Message-----
From: LEDSTRUCTURES(--nospam--at)aol.com [mailto:LEDSTRUCTURES(--nospam--at)aol.com]
Sent: Tuesday, December 11, 2001 11:00 AM
To: seaint(--nospam--at)seaint.org
Subject: Sec 1815 UBC (slabs subject to expansive soils)

Regarding the design of slabs subject to expansive soils: Section 1815 of the UBC  requires a series of beams provided in conjuction with the slab to help resist  the expansion of the soil.  I have heard two different opinions about what this design calls for. #1 ) The beams are actually control joints that allow the slab to crack at predetermined locations. "or" #2) the beams are infact concrete beams that stiffen the slab similiar to the waffle design.  I realize the code is pretty explicite on an actual beam design. But I what to make sure I'm using proper procedure. Can anyone provide asome comments?

Thanks
LSI