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Re: Buoyancy factor of safety

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Thank you for all your responses, I guess I was trying to justify a lower F.S than the 1.67, considering that the ground water will rise to the top of grade, as Daryl suggests, and the water weights are pretty well defined, I just do not see reducing the weight of concrete by 60%

Tarek Mokhtar, SE

Doesn't the load combination 0.6D + H give you a "safety factor" of 1.0/0.6 = 1.67?

On 11/26/2012 2:03 PM, h.d.richardson wrote:

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.

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