huangyhg

adding internal support for a one way single span slab
hi
i have a question here, a builder build a single span one way slab himself, the slab is 150mm, and he placed one layer main reo bar at mid of slab. but it is not strong enough to take the design loads. so he is thinking adding some internal supports.
can any one see if it is workable? from logic, it seems fine. if the support close enough to produce the max +ve and -ve bending less than the capacity, then that is it.
but my question is, because it is only one lay of main bar, and this bar need to use to resist +ve & -ve bending, it will means 2nd curvature create, is it still ok? (i really no idea this point, normally, i put +ve bar to control +ve bending and -ve bar to control -ve bending).
also, the cracking is also my concern.
your comments will be helpful.

there may be large cracks at the top side of slab that were not expected which may be a serviceability issue but i don't see anything wrong in terms of strength if it calcs out in the one-way direction. this would be similar to a multi-story tilt panel with an internal floor support point under high wind load.

i agree 100% with haynewp.
perhaps widening the internal support will help reduce the moment peack a bit and minimise the cracking, but there still will be a lot more cracking than usual.
csd
i would suggest that you calculate the negative bending over the support and then see if this exceeds the cracking moment of the slab. don't forget the dead load is already being resist by the full span and it would just be the live load which would be producing cracking.
if cracking is likely to occur could you sawcut a joint over the support?
thanks guys for these positive comment.

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