Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Beam unbraced length

[Subject Prev][Subject Next][Thread Prev][Thread Next]
If the compression flange is connected to a slab or is periodically
connected to another relatively stiff lateral restraint, then the beam is
generally considered to be laterally braced at those points for flexural
design. If the connection is made at the tension flange, the bracing is
"almost totally ineffective" (Ref: "Fundamentals of Beam Bracing",
Engineering Journal, 1st Quarter, 2001). When the bracing connects to the
beam at other than the compression flange, full height stiffeners may
improve the effectiveness of the lateral bracing (e.g., bracing connected at
the beam centroid with beam stiffeners to prevent rotation at the brace
point). 

I've recently tried to find if any literature indicates that web stiffeners
reduce effective unbraced length of beams, under the theory that the
stiffeners prevent twist of the compression flange relative to the tension
flange, and the tension flange helps keep the beam straight. However, I
cannot find any evidence of this - the literature seems to indicate that the
entire beam cross-section rotates and thus such stiffeners would not be of
benefit without actual lateral bracing attached.  

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


> -----Original Message-----
> From: Reza Dashti Asl [mailto:rezadashti(--nospam--at)hotmail.com]
> Sent: Thursday, March 13, 2003 2:02 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Beam unbraced length (was collector elements)
> 
> 
> 
> Charlie Carter wrote:
> "Lateral torsional buckling is unaffected...unless there is 
> an actual point 
> of direct or torsional bracing. A direct brace is like a 
> kicker angle. A 
> torsional brace is like a pair of stiffeners that extend the 
> restraint of 
> the other flange connected to a slab down to the flange 
> tending to move 
> laterally."
> 
> It seems to suggest that if the top flange is connected to a 
> slab, then a 
> pair of full height stiffeners (welded to both flanges and 
> web?)can be 
> considered a braced point in determining the unbraced length 
> of the beam. Am 
> I getting this right and can we extend this to a beam 
> connected to a roof 
> metal deck?
> 
> Regards,
> Reza Dashti

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********