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Re: Factor of Safety against Uplift

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H. Daryl Richardson wrote:

If you were using a Canadian code you would use 0.85 as a load factor
for the weight of the foundation and 1.5 as a load factor for the wind
uplift.  Putting these together you would have a "factor of safety" of
1.5/0.85 = 1.76.

syed faiz ahmad wrote:

Iam not using 1.5, and am using 2.0 instead. caz I read somewhere, long time
ago (and have lost track as to where I read this),for wind uplift this
factor of safety should be between 2 to 3.5.

Syed:

I'm glad that Daryl mentioned limit states design for overturning which IMHO
is far superior to the allowable stress method at least for overturning
(otherwise it's mostly a pain). One other thing I take from Daryl's comments
is that your local building code should be consulted. What building code
applies in Saudi Arabia? Does it have provisions in it for factors of safety
against overturning?

The other thing you should confirm is that the code that the building
designers used is the same one you are using. This can be a problem. I have
had at least one "design the foundations for" project which was prepared in
the USA to a US model code which had no application in the area where the
building was to be erected. I believe that there is more sophistication
these days so that may not be a problem. But you may still want to request a
copy of their calculations to verify the design assumptions which they have
made. (A good way to get a short course on pre eng. building design!)

Cheers,
John MacLean



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