Should I respect Etabs slab reinforcement above columns to the letter?

[T2ioTD]

There are at least two youtube tutorials on the internet stating that we cannot use the peak reinforcement given by Safe (or Etabs) above columns, and that we should take a nearby (lesser value), because the peak rebar is too much concentrate in narrow area above column.
Is this correct? Any insight on the best practices? how far should I go beyond those peak zones to read the rebar values?
Attached is an example of the matter

 

[OldDawgNewTricks]

The applicable design code will specify the location of the critical section at which you are permitted to calculate the required demand (e.g. at face of support for slabs built integrally with the support).

 

[centondollar]

That depends on how well the boundary conditions in your model reflect the boundary conditions of the built structure. Generally, if you´re using the theory of elasticity and FEA (or hand calculations), you should not arbitrarily pick and choose what moments or shear forces you design to at supports. The plate model can capture a point load (column reaction) and line loads with sufficient accuracy if the element size is small enough and of good quality (i.e., reasonable aspect ratios for triangle or quadratic elements).

The reduction factors found in some codes are derived based on qualitative arguments and experimental correlations, so follow such guidelines with caution.

 

[OldDawgNewTricks]

Do not confuse precision with accuracy. The FEA results are only as good as how well the modelling realistically reflects the physical structure. Typically in ETABS the slab plate elements are connected to a column line element at a single node and the FEA results will not account for the column size effect. So a critical section adjustment can still be valid. The peak moment results from the centerline analysis may not actually occur in the real world. Engineering judgment is required.

 

[KootK]

1) In North America, at least, it is standard practice to take the moment at the face of the column as the design moment.

2) The concept involved (McNichols approach) is based on the fact that the column reaction tends to be skewed towards the edge of the column and that tends to create a prying moment that opposes the centerline model peak moments. See the sketch below.

3) ACI has adopted a simplified version of the McNichols approach and their reasons for doing so are reproduced below.

4) While a highly refined FEM model certain could pick this effect up, I've not yet seen that level of detail included in what I would describe as a "production" FEM model. Think ANSYS, not ETABS.