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RE: Steel beam unbraced length limit

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I agree with Bill.  I don't care so much about the unbraced length as
much as the allowable stresses.  I don't care to use an extremely
slender section even when lightly loaded.  I like to have a reasonably
proportioned section that can withstand unintended loads (strength and
serviceability), fabrication/erection errors, etc. and that doesn't
'flop around' so much when erected.

Eric

Eric R. Ober, P.E., S.E.
Associate
Holbert Apple Associates, Inc.
3423 Olney-Laytonsville Road
Suite 6
Olney, Maryland  20832


-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com] 
Sent: Friday, February 25, 2005 9:12 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Steel beam unbraced length limit

In general, I would not place a limit on unbraced length as long as the
beam meets the code requirements. However, I sometimes get nervous when
the allowable stress based on the code is very low - although this
forces the applied loads to also be very low, it implies that the beam
does not have much lateral stiffness. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Will Haynes [mailto:gtg740p(--nospam--at)hotmail.com] 
> Sent: Thursday, February 24, 2005 1:50 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Steel beam unbraced length limit
> 
> I have designed steel beams with unbraced lengths up to 20 ft 
> before (above "Lr" value).  I have had other engineers tell 
> me they won't design for an unbraced length this high even if 
> it works by AISC equations, I guess due to their fear of 
> fabrication and erection influences on the beam and this 
> being magnified by a larger unbraced length.  Isn't this 
> already accounted for in the AISC equations?  Any thoughts?
> 
> Will Haynes

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