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RE: QUESTION REGARDING CONCRETE MOMENT FRAMES

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Hello Dan,
 
ACI 318-99 references the SEAOC Blue Book, 6th Ed., which reads in Section C404.1, "The geometric constraints for flexural members are based primarily on past practice.  The limit on the width-to-depth ratio is intended to provide compact cross sections that have a reasonably low risk of lateral instability in the nonlinear range of response..."  Farzad Naeim's Seismic Design Handbook, page 308, states that the limitations are based on testing, but does not give a reference.
 
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.
 
Good luck,
Brian McDonald
Exponent
 
(Say "hi" to Ken for me.)
-----Original Message-----
From: Dan Goodrich [mailto:dang(--nospam--at)karren.com]
Sent: Tuesday, November 14, 2000 8:58 AM
To: seaint(--nospam--at)seaint.org
Subject: QUESTION REGARDING CONCRETE MOMENT FRAMES

Hello,
 
UBC 1921.3.1.3 requires the width-to-depth ratio of flexural frame members
in concrete moment resisting frames to be less than 0.3.  Is there any basis
for this, other than observations from practice?
 
We have an architect who would like to use some concrete beams in a frame
that don't meet this requirement.
 
Thanks,
 
Dan Goodrich
Karren & Associates
3707 North Canyon Rd. Suite 8H
Provo, Utah 84604
 
Phone 801-222-0922 (SLC 801-359-2508)
Fax 801-222-0902