huangyhg

shear in slab desig need to be considered or not
i use sap2000 to design slab, i can shear result in slab.
but i use another slab software, the output results don't have shear in slab, just moment and reaction.
someone tell me that slab never fail by shear ?
seem to be right ?
you should design for shear in the slab, be it punching or beam. i would not expect beam shear to be a problem in most slabs (especially two-way slabs) unless you have penetrations or heavily a loaded/reinforced slabs, in these situations it can be of significance.
when in doubt, just take the next small step.

obviously as a general tool for designing slabs, something that is not accounting for shear is a deficient one. check the manual, it may be giving a warning on this. whilst use the other.
it is a very simple check to do by hand.
you absolutely must check shear for slabs. for concrete flat slabs supported on columns, shear failure is usually the critical failure mode. even for wall one shear along say a supporting wall, shear can be a problem.
there's a statement in bridge codes that says slabs designed for moment do not need to be checked for shear. check your code - guidance should be there.
for heavily loaded slabs (>100psf/5kpa) i have seen slabs designed with shear reinforcement at the face of columns where beam shear is going to be the highest. punching shear checks always need to be performed.
apriley, you may be thinking of the minimum shear steel provisions.
all codes require a shear check (long. and punching if applicable). most codes don't require minimum shear steel in some slabs under certain conditions. whether there is shear steel or not you still have to check the shear strength. recent research, and some catastrophic failures such as the place de la concorde overpass in montreal, have shown that thicker slabs (say over a couple feet thick) should have minimum shear steel. this is more of an issue for bridges, unless you're looking at a heavy transfer slab or vehicle access slabs.

punching shear not only need to be checked especially in two way slabs, you also need to include the shear generated by the moment due to fixity between the column and the slab. in other words the punching shear stress distribution around the column is not uniform at the critical vertical stress plane.
if you have drop beams in a two way slab, the shear between the slab and beam is usually not be a problem since the final shear delivered to the column is through the beam which is already checked for shear. the same is true if you have drop beams in a one way slab. the same is also true if the slab is connected to a continuous wall.
the killer for two way slabs is almost always the punching shear (weakest link if i may), the solutions to the punching shear is always one of the following not in any particular order:
1) nelson studs or equal
2) cross shear head made of 2wxx sections moment welded together. a cross head is also sometimes made of top and bottom bars heavily reinforced with shear stirrups.
3) drop panels
4) column capital aka shear head
i suggest designing a slab by hand, at least once, before relying on the software. then, you'd know the answer to the question.
tg
i believe the op was referencing one-way shear or beam action in the original question.
aci 318-05 explicity states that one-way shear shall be investigated in section 11.12.1 "the shear strength in slabs and footings in the vicinity of columns, concentrated loads, or reactions is governed by the more severe of two conditions: beam action where each critical section to be investigated extends in a plane across the entire width or (two-way action)."
one-way shear should be checked.

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