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Re: Unbraced Length of Cantilever

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For a good discussion on effective-length factors for cantilever steel
beams see the SSRC's Stability Design Criteria For Metal Structures, 5th
Edition, Section 5.2.4 and Figure 5.11.  The effective length factor for
cantilevers is a function of the lateral bracing at the support, the
lateral bracing at the end, and which flange is loaded.  Most of the
effective length factors are greater than one.

For the condition you described, full lateral bracing at support, top
flange bracing at the end, and top flange loading, the effective length is
1.4 times the cantilever length.

Rick Drake, SE
Fluor Daniel, Aliso Viejo


Ricky Leblanc <Rick.Leblanc(--nospam--at)> on 12/07/2000 05:36:43 AM

Please respond to seaint(--nospam--at)

To:   "'seaint(--nospam--at)'" <seaint(--nospam--at)>

Subject:  Unbraced Length of Cantilever

Here is the situation.  Cantilever beam (W36 shape) laterally braced at two
points on the top flange (free end and midspan).  These two points offer
bracing against lateral displacement only (no torsional restraint).  At the
fixed end there is full restraint about all bending axes (including
torsional).  Full shear restraint as well.  Under gravity load the top
flange is the tension flange and bottom flange is compression flange (i.e,
the lateral restraint is at tension flange only).  Major axis bending only,
no axial load.  Is the unbraced length of the compression flange the full
cantilevered span, or is it something more?


Rick LeBlanc, PE
Kellog, Brown & Root
Houston, TX

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