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Re: Buoyancy factor of safety

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Whenever I've done these I've assumed the groundwater table for buoyancy calculations was at the surface due to rain saturating the backfill. I've also considered only the soil directly above the submerged tank (or footing extension for concrete cisterns); I've not considered the soil sloping away from the tank wall at 60 degrees or anything like that. I also consider the buoyancy acting on the concrete weights or the footing.

For safety factors (I prefer to call them ignorance factors) Canadian limit states codes would use 1.25 for the dead load (or other accurately determined load) being the force to be resisted and 0.85 for dead weights resisting the force. This results in 1.25/0.85 = 1.47, which is close to 1.5. I would not consider anything less than 1.5.


H. Daryl Richardson

----- Original Message ----- From: "Craig Hawe" <chawe(--nospam--at)>
To: <seaint-seaosc(--nospam--at)>
Sent: Monday, November 26, 2012 11:48 AM
Subject: RE: [SEAINT-SEAOSC] Buoyancy factor of safety

For sliding and OTM it is typical to use 1.5 with wind and seismic
included.  I would suggest at least 2.  How sure are you (or the geotech)
of the water table?  If you're not sure maybe more.

Craig Hawe, PE, P.ENG.

-----Original Message-----
From: seaint-seaosc(--nospam--at) [mailto:seaint-seaosc(--nospam--at)] On
Behalf Of Tarek Mokhtar Sent: Monday, November 26, 2012 11:40 AM
To: seaint-seaosc(--nospam--at)
Subject: [SEAINT-SEAOSC] Buoyancy factor of safety

What would an appropriate factor of safety against floatation of a
submerged residential basement be? would AISC load combination 6 ( 0.6D +H ) be applicable in this situation?
Tarek Mokhtar, SE

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