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Re: CBC 1921.4 Frame Members Design

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As the code states" including earthquake effects ".....the seismic force could uplift the frame on one side so that the compressive axial forces in the columns reduce a lot. That's my interpretation
 
Simon
----- Originage -----
Sent: Monday, November 03, 2003 2:32 PM
Subject: CBC 1921.4 Frame Members Design

Hi Concrete Gurus,
 
Per CBC section 1921.4 - an earthquake load resisting frame member subjected to bending and axial loads should have an axial load exceeding "Ag f'c / 10". This is usually a frame column.
 The shear strength of such a member should meet the shear demand per section 1921.4.5. In section 1921.4.5.2 it is suggested to ignore the the shear capacity due to concrete (Vc=0), if the conditions per items 1 & 2 are meet.
 
My question is - How can condition # 2 ever be meet? i.e.
 
Item #2 states : "The factored axial compression force including earthquake effects is less than Ag f'c / 20"
 
Summary::
Section 1921.4 is addressed only when Pu is greater than Ag f'c / 10, Then how could Pu be less than Ag f'c / 20 in order to use Vc=0?
 
Please comment.
 
Thanks,
Nitin
 


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