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RE: QUESTION REGARDING CONCRETE MOMENT FRAMES

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Good point(s) Paul.  In my mind I was picturing something that was marginally less than 0.3 - if the beam is anticipated to be much more slender, then boundary element type detailing would be required.  I also agree (and should have added to my post) that any relaxation of the code requirements, even if justified by analysis and approved by the building official, should never be taken lightly.
 
Brian
-----Original Message-----
From: Paul Crocker [mailto:paulc(--nospam--at)ckcps.com]
Sent: Tuesday, November 14, 2000 1:09 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: QUESTION REGARDING CONCRETE MOMENT FRAMES

You should also consider that as the beam height increases, the ability of the confinement steel to resist the tendency of the sides of the beam to expand/blow out in the compression zone is diminished.  This would be similar to having a long wall boundary element with only one large hoop around it and no intermediate cross ties.  Even if lateral stability could be assured, I would expect that cross ties would need to be added to maintain ductility in a beam with an unfavorable aspect ratio.  The aspect ratio is something that I insist upon maintaining.  If you have a problem making the architect understand the issue, it is spelled out quite clearly in the code; it is not something that takes a long series of intricate and moderately subjective computations to arrive at.  Most reasonable architects understand that they ought not do things that are expressly forbidden in the code. 
 
Paul Crocker
 
 
"Based on that, I would venture to say if you have an alternate means of assuring lateral stability/bracing after much cracking, relaxing the width-to-depth limitation would be justified.