Re: FTG UPLIFT

We always use 0.6 on the foundation weight to provide a safety factor of 1 / 0.6 or 1.67 against uplift.  This also keeps us in compliance without argument.

 

We see the 1.67 safety factor as in effect replacing the long-standing 1.5 factor against overturning. 

 

For uplift anchors however we use 1.0 Dead as the safety factor is included in the ASD material specification.

 

If pressed when assessing an existing condition; we don't say yay or nay but state the safety factor provided and request instruction from the client/official as to how to proceed.

 

Steve Adams

----- Original Message -----

From: William Haynes

To: seaint@seaint.org

Sent: Monday, November 21, 2011 9:26 PM

Subject: FTG UPLIFT

I wanted to see how many are using 0.6xFTG Self Weight of the footing when checking uplift due to wind or using the entire footing weight, 1.0xFTG Self Weight to help resist uplift. There appears to be several engineers that use 0.6x(everything else dead load except the footing) + 1.0x(FTG Self Weight) to check versus 1.0xGross wind uplift. The concrete has no allowance to be lighter than what you assume, and the footings have to be consistently dug to at least the dimensions you specify on your drawings. Is there anyone involved in forensics of metal buildings that have seen the footings uplift out of the ground when the code prescribed 0.6 wasn't factored on the footing self weight?



Will Haynes