concrete slab - shear reinforcement - better option?
concrete slab - shear reinforcement - better option?
(OP)
Hi, Im reinforcin a RC slab (200 mm thick). Since shear forces are still larger than slab shar capacity, I have to add shear rebars.
Blue line in the picture is a virtual crack line - so no matter which option I choose, shear reinforcement (rebars) has to cross this line.
I like 2nd option better but option one is much easier to make since I have only 200 mm between walls.
Which option would you suggest based on your experience and why?

Blue line in the picture is a virtual crack line - so no matter which option I choose, shear reinforcement (rebars) has to cross this line.
I like 2nd option better but option one is much easier to make since I have only 200 mm between walls.
Which option would you suggest based on your experience and why?







RE: concrete slab - shear reinforcement - better option?
RE: concrete slab - shear reinforcement - better option?
RE: concrete slab - shear reinforcement - better option?
RE: concrete slab - shear reinforcement - better option?
For a short cantilever transfer like this one, the slab thickness should be based on the minimum depth to satisfy shear without requiring shear reinforcement, and I would make sure I am not near the limit. There can be no logical justification to try to do it with a 200mm slab and then add shear reinforcement to make it work.
And I would make sure there is some fully developed bottom steel in the cantilever as well.
RE: concrete slab - shear reinforcement - better option?
Based on your previous thread, I suspect that you're pretty close to making it work without shear reinforcement. Is that correct? If so, perhaps an economical strategy would be to use higher strength concrete. It's diminishing returns because of the square root business but, if you don't need much, you might be able to get it that way. Another strategy, in a similar vein, might be to keep the cantilever propped until the concrete reaches it's 56 day strength which, presumably, would allow you to take advantage of an f'c that's a bit higher than the conventional 28 day strength.
It is my opinion that shear friction is not a valid strategy for resolving diagonal tension issues. In fact, I reject it for any application where the resisted displacement has a significant component perpendicular to the assumed shear friction plane. I see this a lot with folks trying to circumvent appendix D breakout issues as well. They get tempted by the notion that the resisted displacement can be conceived of as having a component parallel to an inclined shear friction slip plane. When you drill down on it conceptually as I've done below, however, I think that the logical fallacy of it becomes apparent. There really is not any tendency towards slip parallel to the shear plane. And that neuters the strategy.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: concrete slab - shear reinforcement - better option?
RE: concrete slab - shear reinforcement - better option?
Though it is close to a strut/tie / deep beam situation, so make sure the cantilever top flexural reinforcement is fully developed at the end of the cantilever.
I doubt that any design code would allow you to use the 56 day concrete strength for shear, no matter when it is loaded! All design codes I know say to use the 28 day Characteristic strength!
RE: concrete slab - shear reinforcement - better option?
Also how did you calculate your shear forces?