Is Shear Reinforcement Req'd. for Bottom of Columns?

[MrFurleyEIT]

I have got a question about shear reinforcement(a.k.a. stirrups, ties or links) for the bottom of column bars that are embedded in deep slabs or footings, esp. for deep footings (>= 36").

Do we need to provide stirrups in this part of the column? Please see Sketches #1 abnd #2 below. Should it be like Sketch #1, i.e. No stirrups or shear reinforcement provided in the part of the column embedded in the slab?

Sketch #1:


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Or should it be like Sketch #2, i.e. Stirrups or Shear Reinforcement provided in the part of column embedded in the column?

Sketch #2:


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Please submit your votes now.

I would have thought that it would be Sketch #2 but I would like to hear the opinions of people familiar with this situation, or foundation engineers who deal with this on a daily basis.

ACI 318-05 in Section 11.5.6.1 (Minimum Shear reinforcement) on Page 157 states that, "A minimum area of shear reinforcement , Av min, shall be provided in all reinforced concrete flexural members (prestressed and nonprestressed) where Vu exceeds 0.5 * phi * Vc, except:

(a) slabs and footings;

(b) Concrete joist construction defined by 8.11;

(c) Beams with h not greater than the largest of 10 in., 2.5 times thickness of flange, or 0.5 the width of web.

Is the shear reinforcement required in the part embedded in the slab, and if not, why not? Is it because there is negligible shear there? Is it because that part of the column is meant for embedment only? Or is it because it is too difficult for the Contractor to get the ties in there. Thanks in advance.

 

[bridgebuster]

For a bridge the answer is Yes, Sketch 2.

 

[csd72]

For a building not in a seismic zone, with slab on all 4 sides the ties are only required above and below the slab.

I am not sure if there are seismic rules that dictate otherwise.

csd

 

[JAE]

See ACI 318,
Sections 7.10.5.4 and 7.10.5.5