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Shear strength has to do a lot with aggregate size used. A 10,000 psi concrete is high strength concrete and high strength concrete does not has normal or large aggregates. The use of small aggregate limits shear capacity. To sum it up in one line, try designing a beam without shear reinforcement with aggregate interlock as the primary mode of shear transfer. you will understand the "whole" thing. Cheers

.you cant really say that.. what about the w/c ratio.. what about the distribution of aggregate size ( i mean sieve analysis distribution) what about the mix design of the subject. what about the chemical properties of aggregate? there are so many things to look for. If you did a test and noticed that.. share the results.

Take it the other way, if your load creates compression in the support and its a not in a disturbed region, take critical shear at distance d from the support.

Drawing shows top rebar on all sides

like umar said votrex shedding is something that makes things vibrate "perpendicular" to the plane of the wind.

why was this thing moving up and down? It seems wind was trying to move horizontal members up and and vertical supports were pulling it back but how is wind able to generate such force on this thinner surface area. Shear failure of connections must have triggered the fall of Sign board.

drawing is unclear as is your question. For me it seams like top reinforcement has been provided on all four sides at the spacing of half of bottom reinforcement.

Beam can be loaded at bottom, imagination respects no boundaries.One condition is of inverted T-beam. Why is critical section for shear at a distance 'd' from the face of support for other cases? if you can answer it than you can answer your own question. It is because shear crack develops at least at a distance d from support in other cases but it is not the case in this particular condition.

First of all you should refer to ACI 318 by year too. I mean the clause you mentioned is from ACI 2005 or 2008. Because numbering of the clauses has been changed. So 8.2.1.6 in 2005 is different from 8.2.1.6 rather there is no such 8.2.16 in 2008 version. Anyway, Regarding your question of minimum reinforcement. Always remember that reversal of moments or forces takes place for example in wind or eartquake. So your positive moment becomes negative and vice versa. For example in a blast loading your slab may crack because in middle span the top reinforcement you provided was insufficient. That is the region where you can ignore the reinforcement generally. Thats why ACI has some limits for minimum reinforcement, although the minimum reinfocement will still not be enough for blast loading but thats another issue. Minimum reinforcement is different than the temperature and shrinkage reinforcement. For example Temp reinforcement (0.0018bh) is the total area of steel you have to put in slab or footing. Put half at top and half at bottom or total at mid..whatever..ok! But 0.0018bh if you talk about min flexural reinf you have to put full at top and and full at bottom.