Weak Story Shear Calculation

[Canucks1010]

Hi All,

I have a question for calculation weak story shear in an OMF.
Assuming we have strong-column, weak-beam scenario, the story shear capacity = Mb / story height.

If we have two different beam sizes at top and bottom of the column, do we then do (Mb,top /2 + Mb,bot / 2) / story height?
See attached example

 

[HTURKAK]

I assume you are looking for column shear requirement for OMF.

The following clause from ACI 318 ;

18.3.3 Columns having unsupported length lu ≤ 5 c1 shall have ΦVn at least the lesser of (a) and (b):
(a) The shear associated with development of nominal moment strengths of the column at each restrained end of
the unsupported length due to reverse curvature bending . Column flexural strength shall be calculated for the factored
axial force, consistent with the direction of the lateral forces considered , resulting in the highest flexural strength,

(b) The maximum shear obtained from design load combinations that include E, with ΩoE substituted for E.

 

[chris3eb]

OP - I believe you're asking about checking to see if you have a weak story irregularity, not necessarily trying to find the design shear for the column, right? To do this check, you're looking for the total lateral strength of a story versus the total lateral strength of the story above. I think that to find the lateral strength of a story, you would treat each story as a one-story fixed-base frame (if your first story is pinned, it should still be pinned for this check), and add a lateral load until your first member reaches its capacity. So the "total lateral strength" or "story shear capacity" would not be dependent on the lower beam.