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Re: diffential settlement- Reply

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Well thank you Brian and Todd,

You're both right about there not being much literature on recommendations for
slab-on-grade flatness.  I did find something in ACI regarding new
construction and the acceptable tolerances that dealt with F factors (I
believe Brian mentioned this in his response).  (Boy was that dry reading.)
In fact I've heard that engineers who are in litigation have referred to this
article as a baseline. 

I should have given some background as to what prompted this whole thing.  As
I said before this is a tilt-up building that was built in about 1978.  The
tenant of the building informed the owner that a panel joint had separating,
"as if the panel had rotated about its axis."  Our firm was asked to
investigate the cause.  The panel joint had in fact separated and the chord
steel (2-#5) at the top of the panel had completely fractured.  Since the
panel joint was at the end of the diaphragm and not the middle and no other
panels appeared to be separating we did a local manometer survey to check the
levelness of the slab.  This produced differential elevations that lead us to
believe the foundation had a settlement problem.  A manometer survey of the
entire slab was recommended and has since been performed.  The results of the
latest survey show in fact that the slab-on-grade of the area in question, has
uniformly settled relative to the rest of the building quite a bit.  (The
contour lines suggest some deep seated consolidation.)  

We are suggesting that the owner hire a geotechnical engineer to investigate
the cause and if in fact it will continue.  Obviously, any repair that needs
to be made on the chord steel must be done after we find out what is causing
the settlement problem and the solution to mitigate it.  So the drama
continues....

Well, I was surprise that I only received two responses, but then again this
is more on the civil/geotechnical side however it did eventually effect the
structural side.  Funny how that works :-) !!!

By the way, Todd, I completely understood when you mentioned "beating a
subject to death" we engineers tend to do that best :-)  .

Thanks for the input...and if you have any more, I'd appreciate it.

Michelle Kam-Biron, S.E.