Concrete Moment Frame - Strong Column Weak Beam at Interior column

[LCMKS]

I couldnt find an (e) post for this so here it goes...

Problem: I have a single storey building with concrete moment frames. I am aware of the Mnc>(6/5)Mnb criteria that that ACI 21.4.2.2 uses to ensure beam yielding prior to column yielding. For interior columns (where i have two beams frame into i column)I would require a very large column section to satisfy the above equation.

Question: Is there a provision where I would not require such a large column flex capacity in the ACI somewhere or even in the IBC 2006 ? Or even in the 2007 California Building Code?

Your help would be much appreciated!

 

[JAE]

Consider 21.4.2.3 - if you can't meet Equation 21-1 in21.4.2.2, you can add additional transverse reinforcing.

Also, the commentary suggests (in ACI 319-02 - 4th paragraph of the 21.4.2 commentary) that if you don't meet the weak column criteria at a joint, then "any positive contribution of the column or columns involved to the lateral strength and stiffness of the structure is to be ingnored..."

...but you can't ignore "negative" contributions such that the siesmic demand is reduced because you ignore the stiffness contribution of these columns.

 

[Taro]

It's not just a commentary suggestion. 21.4.2.1 mandates that any column that doesn't satisfy the SCWB criteria cannot be used as part of the lateral system.