bottom cracks on flat slab

huangyhg

bottom cracks on flat slab
hi
while inspecting a collapsed ceiling (suspended plaster) i noticed hairline cracking accross the soffit of a concrete flat slab. the cracks where about 200mm apart and where approximatly uniform running with the span.
my assumption is that these are tension cracks on the line of the slab re-bars but is this normal or acceptable.
i have no involvement in the building todate so do not know of the construction or design,  but should i report this to the building manager as a matter of concern ?
tson
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you say they are running "with" the span of the slab?  in other words, they are parallel with what would be the main bottom reinforcing in the slab?
if so, they are most likely shrinkage cracks as flexural cracks would be perpendicular to the slabs span direction.
if they are diagonal in plan, then they may be due to tensile stresses built up via deflection of the slab relative to surrounding stiff beams at corners.