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

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You need to be a bit careful here.  

1st - You will not be able to resist the expansion of the soil.  You can
resist the EFFECTS and in reality you will only be able to control the
effects to a degree.  The only way to totally mitigate the effects of soil
expansion is to use drilled piers and a structural slab over a void.

2nd - This is only applicable to slab-on-grade FOUNDATIONS.  You can
construct the structure to be supported on drilled piers, and place a
slab-on-grade to bear on the soil with few provisions for expansive soil.
The key to invoking Section 1815 is if the slab on grade is a foundation.

Basically what Section 1815 is trying to do is tie everything together so
that the slab on grade will be able to serve as a foundation.  The slab will
move, but the differential movement will be limited by the stiffening of the
slab and beam system.

Harold O. Sprague

> -----Original Message-----
> From:	LEDSTRUCTURES(--nospam--at) [SMTP:LEDSTRUCTURES(--nospam--at)]
> Sent:	Tuesday, December 11, 2001 11:00 AM
> To:	seaint(--nospam--at)
> 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 

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