contraction joints in suspended slabs

huangyhg

contraction joints in suspended slabs
what is everyone's thoughts on placing sawcut contraction joints in suspended slabs? i routinely place them in slabs on grade but am unsure about the wisdom of placing planes of weakness in a structural slab. most of my suspended slabs are designed with integral beams and removable forms and are tied to the walls. i have not been able to find any guidance on this situation. thanks.
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i can't think of a situation in which a saw cut in a suspended slab would be advantageous.
exposed parking decks, stadiums, unfinished office floors, roofs and other exposed concrete elements.  if you are carpeting or tiling, don't bother.  contraction joints take the place of naturally formed cracks (ie you're going to have a crack near there anyhow).
the advantage of a contraction joint is that you can put sealant in it during construction, you can designate a profile for the joint (rounded edges), and it looks better.
a saw cut joint only works as a contraction joint when you saw cut the concrete before it cracks.  this means you have to cut the concrete within hours of casting it (good luck with that).  
i don't put them in suspended slabs or composite steel beam/joist systems, i put them in topping slabs for precast.  
definately not in suspended slabs.
if you need movement joints in slabs then provide a full movement joint in the form of an edge supported on a corbel or double frames with a full joint between them.
google it and you will find many references on this.
expansion joints at floors when wanted or required for proper account of rheological movements (temperature and shrinkage mainly) need be purposedly designed. the olden practice was to duplicate columns at each side of one of these joints, but today it becomes everyday more common to use shear contraptions sold by specialty providers that allow movement perpendicular to the face of the joint and horizontally as well if so wanted or required, whilst coercing vertical relative displacement and even support if one of the sides is rigid enough.
ishvaag,
provision of double columns at a movement joint is not an "olden practice".  it is the right way to do it.  halving joints and corbels are a major cause of modern building structural distress and serviceability issues.
who made this post so wide?
ditto; use cast contraction/movement joints where required for large buildings.
stay well away from sawcut joints for suspended slabs.
for parkades, i've often used a "goldblatt groover" to provide a joint to be filled with a flowable joint filler. i've not used a saw.
dik,
but the question was about suspended slabs.  surely you don't need a joint filler in suspended slabs where the top of the slab is in compression.
joints are made at supports and rely on the reinforcing steel. yes, it's designed with this in mind.