Criterion for classifying a beam-column into flexural and compression

[DST148]

Ref ACI 318-05. The confining reinforcement requirements depend on the type of behavior of the member, namely flexural and compression. A frame member (beam-column) typically is subjected to both - bending and axial load. I am not aware of any criterion in the Chapters 1 thru' 15 which classifies a member broadly into either a flexural or a compression. However, section 21.3.1.1 classifies a frame member as a flexural if Pu < (Ag. f'c /10) .
For example a column / pier / pedestal subjected to axial, moment, and shear forces but falls into the category of a flexural member per definition given in 21.3.1.1. Now if shear Vu < (0.5. Phi. Vc) then no shear reinforcing is required in a flexural member per section 11.5.6.1. In that case the ties could be provided just to keep the longitudinal reinforcing in place.
The question is: Can section 21.3.1.1 be used as a criterion for classifying a frame member (beam-column) into either a flexural or a compression member for deciding confining reinforcement requirements? (It is assumed that the member is not part of a LLRS and not in a high seismic risk region)

 

[ash060]

It depends on the steel strain. If the steel strain is less than 0.004 than it would be in the transition zone, but it would not meet the requirements of a flexural member so it would be a compression member and have to meet those requirements.