is it important to use structural join

huangyhg

is it important to use structural joint
dear structural
i have a flat slab without beams 10m*90m , rectangular , dose i have to use a structural joint in that  

flat slab on grade without grade beams, or is this a flat slab reinforced concrete structure?
you can have a large flat slab like this in either case without structural joints, but it takes compensation for temperature and shrinkage as well as general concrete cracking through other means.  shrinkage compensating admixtures, post-tensioning, proper concrete mix design, etc.
curing will not reduce the total shrinkage cracking, but in fact may delay the onset of the total plastic shrinkage component.  often that leads to greater cracking once components are "locked in" on site.
post more details; there are lots of people around to help!
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
yes its a reinforced concrete over columns and the cracks happen ,it was a real cracks , do you have an idea how to deal with  that slab
from your second post, i assume the slab is built and has cracked.  it is impossible to know from your limited description whether the cracking is significant.  if you can describe the structure in terms of thicknesses, size and spacing of columns, any restraining walls, reinforcing details, etc. perhaps we can assist.
thers a deep cracking  1 mm  it shown  in slab 300 mm thickness with columns every 6 m on edges
do the cracks go across the 10 metre direction?  how much reinforcement exists?  are there restraining elements near the ends?
dear  , it works along 10 meter , but in fact theres no reinforcement in top x or top y , the reinforcement exixt in bottom x,y only becouse it works ìn posative only , and the code her accept with no reinforcement

sounds like you don't have reinforcing to restrain the counterflexure which occurs accross / adjacent to the columns... i would have expected cracking if i saw the drawings prior to construction.
this is a very old and well known problem.... if you prop a flat slab, it will behave as if there were beams along the shortest connecting points between columns.  the cracks won't be as big, or deep, or as well located, but they will occur.
whether or not they are significant depends on too many factors to try and help you with my limited experience.  sorry, and good luck, but i'm just an observer from here on in.
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
with no top reinforcement, you would expect flexural cracking in the top of the slab, generally across the slab at the column lines.  these cracks would not extend through the slab.  any cracks which extend completely through the slab would probably be direct tension cracks caused by restraint.  if this type crack is 1 mm wide, that would indicate that an inadequate amount of shrinkage control reinforcement is present.  it would be interesting for us to know your location.
thanks for your nice answer youngstructural and you have a real nice answer, and thanks to hokie ,you also born in 1966 , it was a very sharp answer and i think you give a real suggestion   ,if there is any answers for treatment of cracking in flat slab ,i mean that happen according to temperature , we  appreciate your suggestion
structuralll,
thanks for the compliment, but 1966 is the year i graduated from university.  you need to determine first if the cracks are structurally significant before you consider any remedial action.  without further description of the structure, i am afraid that i can't be of further assistance.