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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)
 Reply-to:	seaoc(--nospam--at)
 To:	seaoc(--nospam--at)
 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
 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
 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