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Re: cantilever column system

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Paul,

I don't see why you wouldn't be able to do as you've done before.  I think you can argue that the columns are cantilevered above the 8'-0" wall plate.  Therefore, use R = 6.5 for sheathed walls, but amplify the point load at the top of columns by a factor of 6.5/2.5 = 2.60, and check the bending and deflection of the column with a height of 3'-0."  The lateral force from the 11'-0" plate height is adequately transferred to the shear wall, and the column is effectively braced for a height of 11'-0" in one axis.

Also, depends what jurisdiction you'll be jumping through hoops for.  But, this approach seems very logical and reasonable.  Engineering judgment.   Hope this helps.  Good luck.

On Fri, Sep 18, 2009 at 1:52 PM, <PFFEI(--nospam--at)aol.com> wrote:
I have a condition on a project with 11' plate height, with clerestory glass approximately 3' above an 8' tall shear wall, in a light framed 2 story wood framed single family residence.  I intend on using steel columns to transfer roof lateral load to drag at top of shear wall, and would not consider this to be a true cantilver column system.  Prior to the new code, i have been able to justify design as a beam / column drag that transfers loads to drag beam at the top of the shear wall, with the column is designed for an amplified force like an offset on a beam.  I would use the R value for plywood shear wall building rather than cantilever column system.
 
I do not have experience with the new code using this approach.  The new code seems very defined about cantilever systems requiring that they comply with moment frame design requirements. 
 
I am looking for an opinion on whether a beam column model is a reasonable approach for this case.
 
Thanks in advance,
 
Paul Franceschi



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David Topete, SE