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Criterion for classifying a beam-column into flexural and compression

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DST148

Structural
Joined
May 2, 2010
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US
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)
 
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.
 
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