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Re: Cm

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The LRFD Specification omits the "Rotational Restrained" wording.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

***********************




                    Mark Pemberton
                    <Markp(--nospam--at)lbdg.com      To:     "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
                    >
                    02/20/02 01:53       cc:
                    PM
                    Please respond       Subject:     Cm.
                    to seaint
                                                                                                                 .





Per the 9th edition of the AISC, H1, Cm part b states
"For rotationally restrained compression members in
frames not subject to transverse loading between
their support in the plane of bending, Cm = 0.6-0.4M1/M2"
What if you meet all this except the "rotationally
restrained" portion?  What exactly is meant by rotationally
restrained?  Are these members with moment connections?
If so, where do gravity columns with eccentricities fall?
RISA uses this formula for Cm on all members while SAP2000
by default uses Cm = 0.85.  The "Civil Engineering Reference
Manual" (by Lindeburg) omits the "rotationally restrained"
qualification for using Cm = 0.6-0.4M1/M2.  Any input is
appreciated.


Mark Pemberton, P.E.
Project Engineer
Lionakis Beaumont Design Group
1919 19th Street
Sacramento, CA 95814
Phone: (906) 558-1900, ext. 300
Fax: (916) 558-1925
www.lbdg.com


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