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Re: Uplift resistance

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There are a lot of options for solving your uplift
problem, but its kind of hard to tell which is best
without seeing your drawings.  In addition to the
suggestions noted by others, here are a couple more:

If footing with net uplift is near some adjacent
footings you run a grade beam between the footings
immediately to the left and right of the one with the
uplift ?problem? and use the dead load on the adjacent
footings to hold down one with uplift.  This is
usually most efficient for when you have really big
uplift forces.  Your uplift forces are probably not
high enough to justify this solution.

If the uplift is occurring on a column that?s in a
braced frame, you could place both of the braced frame
columns on a common rectangular footing and stretch
the length of the footing as needed to keep your soil
pressure at or below the allowable pressure and to
maintain your safety factor against overturning.

You could jog the bracing around as you go down the
building to distribute the uplift forces around to
multiple columns.  If the uplift is occurring from a
braced frame that?s comprised of two columns with
diagonal bracing between them from roof to foundation,
try shifting the bracing over a bay for one or two
floors to spread the load over three columns instead
of two. 

Add another braced frame to take some of the load off
the one that has too much uplift.

All of the above solutions have one thing in common ?
they make use of the dead loads in adjacent columns to
help resist overturning moments and minimize the need
to add blobs of concrete solely for the purpose of
providing an ?anchor? ? however in some cases this
might be the most economical solution (especially for
fairly small uplift forces)!  

Adding tension piles sounds kind of expensive ?
especially if there are no other piles on the project
(which I?m assuming there are not.) 

Hope this helps.

Cliff Schwinger

--- "Seth W. Cutler" <seth(--nospam--at)> wrote:
> I'm working on a steel building which has uplift
> forces in the order of 
> 50-170 kips in isolated locations.  The foundation
> design is spread footings.
> Any suggestions?  Do I have to go to piles to
> accomplish this?
> Thanks,
> Seth W. Cutler
> R. L. Morrison Engineering Co. 

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