Luceid
Structural
- Feb 16, 2023
- 223
Has anyone run into an issue with punching shear where the shear reaction is significantly higher relative to the moment demand, causing a sort of moment reversal when you move the shear to the centroid of the punching perimeter? The only reference I have found to this phenomenon is in Bondy's Post Tensioned Principles book, where he claims that this kind of reversal doesn't make realistic sense, since the moment would not magically reverse in the slab to be in accordance with our punching shear calc, but I haven't been able to verify this thinking anywhere else (and it seems to defy statics in my head). See diagrams below:
1. Descriptive case
2. Column Reactions in Section
3. Shifting Shear from column centroid to centroid of shear perimeter, equivalent moment of Vu*e is required to satisfy the statics of "moving" the shear
Typically, this Vu*e moment reduces Mu to create a lower moment demand on the punching shear perimeter, which is typically great, however in this case it goes too far. Essentially, if Vu*e happens to be really large relative to Mu, the net unbalanced moment for punching shear flips!? Realistically this doesn't make sense, which may be why Bondy's literature cuts off Mu-Vu*e at 0, not allowing it to flip signs. Has anyone dealt with this before and/or have some reference information about it? Thanks all.
(Code reference is ACI 318-19, column reactions are being pulled from FEM software)
1. Descriptive case
2. Column Reactions in Section
3. Shifting Shear from column centroid to centroid of shear perimeter, equivalent moment of Vu*e is required to satisfy the statics of "moving" the shear
Typically, this Vu*e moment reduces Mu to create a lower moment demand on the punching shear perimeter, which is typically great, however in this case it goes too far. Essentially, if Vu*e happens to be really large relative to Mu, the net unbalanced moment for punching shear flips!? Realistically this doesn't make sense, which may be why Bondy's literature cuts off Mu-Vu*e at 0, not allowing it to flip signs. Has anyone dealt with this before and/or have some reference information about it? Thanks all.
(Code reference is ACI 318-19, column reactions are being pulled from FEM software)
