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Fw: concrete shearwall "Shafts"

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I have wondered about this particular subject in the past as well.

The problem as I see it is that when analyzing such a section, it SHOULD be
assumed that the elements all act together as a unit, in order to properly
account for the overall stiffness of the section.  But I think the UBC is
limiting the effective flange widths for design, not analysis.  Thus, if
you have a square section, you might try concentracting the flange
reinforcement in the corners, for both directions, with minimal
reinforcement along the "web" lengths, while using the results from an
analysis that models the shaft as a unit.

A caveat, though:  I feel that the effective flange widths can prove to be
UNCONSERVATIVE when you are trying to calculate the moment capacity of the
section for hinge development (for Vo calculations).  In this case,
underestimation of the effective flange widths would lead to a low Mo and
low Vo.

T. Eric Gillham PE

> From: Tim Terich <tterich(--nospam--at)>
> To: 'seaoc(--nospam--at)'
> Subject: concrete shearwall "Shafts"
> Date: Friday, October 23, 1998 8:25 AM
> 1997 UBC questions,
> does the code allow the use of stairway and/or elevator shafts (or
> cores)
> areas as complete lateral force resisting elements?  Section 1921.6.6.2
> seems to 
> prevent using "boxes" as lateral resisting elements, due to effective
> flange
> limitations. I would think that a "box" section would behave as a box,
> not a collection
> of walls with limited boundary flanges.
> if anyone has any experience, or different interpretations of this
> section, please let me know.
> thanks,
> Tim 
> _________________________
> Tim Terich
> Century West Engineering Corp.
> 825 NE Multnomah, Suite 425
> Portland, OR 97232
> v(503) 231-6078
> f(503) 231-6482