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Re: CONC - Stripping of Deck Forms

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In a message dated 97-08-13 20:48:10 EDT, you write:

<< Subj:	CONC - Stripping of Deck Forms
 Date:	97-08-13 20:48:10 EDT
 From:	PRSE(--nospam--at)aol.com
 Reply-to:	seaoc(--nospam--at)seaoc.org
 To:	seaoc(--nospam--at)seaoc.org
 
 I have a project in Santa Monica, which is 3 stories of wood over a
 structural concrete deck over parking.  The deck is specified as 4000 psi
 concrete.  The contractor wants to know if he can strip the forms after 7
 days, assuming the concrete has reached full design strength.  I am hesitant
 to let him do this because I am afraid the concrete will not be quite cured
 enough and the early removal of the forms may result in some
deflection/creep
 problems.  As an alternate he has offered to reshore at 7 days with posts
 spaced further apart than the original shores.  His goal, of course, is to
 save money by returning the rented shores as soon as possible.
 
 Any thoughts and/or experience with this issue would be much appreciated as
 they are scheduled to pour on Friday and are looking for an answer from me
 shortly.
 
 Thanks in advance for your advice / opinions.
 
 Bruce Resnick
  >>

Standard practice as I understand it is to pull shores at 14 days and provide
50% reshores.   We require that the concrete must have achieved a minimum
strength of 0.75 f'c before doing reshores and that 100% shores have been in
place for 14 days minimum.  

The problem we have found is that when they pull out 50% of the shores, they
actually pull out 100% of the shores (the slab now deflects) and then 50% of
the shores are replaced under the deflected slab, obviously not what you
intended.  In your case, are the shores set up such that 50% can be removed
without having to remove and replace the other shores?, thereby reducing the
amount of deflection.  You might want to tell them the required locations for
the 50% reshores you want kept in place.

You may also want to review ACI standard recommended practice for concrete
formwork (ACI-347), I think this is the correct committee number.

Michael Cochran