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RE: ConcreteOne Way Joist and Beam

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My favorite reply to contractors is "Rip it out and do it correctly this
time" which their response to that is something that I should not repeat.  I
then proceed to tell them that this is the last option.  
If the concrete "looks" different from the others then it probably is.  So I
would suggest analyzing the cylinders and cores to find any deleterious
materials which may have made it into the subpar concrete.  Odds are you
will find something and if it is detrimental to concrete then the concrete
has to be removed.  If nothing odd is found then the possibility of
post-tensioning and/or carbon fiber reinforcing could be considered to help
the flexural stresses.  
Load testing would be my second to last option to consider ... which reminds
me of a story.  A large university was constructing an addition to their
football stadium.  The designers chose to straddle the existing construction
with a cantilevered concrete structure.  All went well.  One of the parties
decided to load test the structure to three times the design LL.  My only
guess is they did not trust that cantilever thingy or because some rowdy
students/alumni might try to jump up and down during a game.  Surprise,
surprise!  The concrete cantilever developed a hairline crack at the
support.  Of course it would, concrete does crack when subjected to loads
higher than design loads; however, the structure does not collapse after it
develops a hairline crack.  Does not matter though, the university decides
the structure is unsafe and must be post-tensioned to close the cracks and
"prevent failure."  This "fix" goes smoothly and opens on time to get the
lucrative ticket revenue flowing in.  Then, the university sues the original
design engineer to recover the costs of having to "fix the deficient
structure."  No hard feelings, Mr. Engineer and former Board of Director
member, it's just business.  What's a few million dollars between friends?
It is strange situations like the one above that makes me wonder ... are all
of the safety factors we use enough?  When I first started working, I was
teamed up with some engineers that were about to retire (what other business
would a wet-behind-the-ears graduate be teamed up with a professional with
45 years experience, nearly twice my age?).  Their common method of design
was to perform the calculations and determine whatever property they needed
to select a member ... then double it.  Or precisely calculate the load per
the building code ... then triple it.  
Just something to think about before you make your decision.  Hope this
helps.  Happy Holidays to all!  BTW, does any one know something about this
Y2K event? :o)
Happy New Year!

William J. Keil, P.E.