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Re: Half-allowable stresses for masonry

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As correctly pointed out by Paul Feather, the idea behind the half allowable
stress provision is to limit the applied load, rather than to increase the
steel reinforcing area. That's why the allowable steel stress is not
reduced, but only the masonry stress.

Of course all this discussion belongs to the ASD method, which in fact could
be considered as outdated since the Ultimate Strength Design method is also
available in the UBC. In this method the special inspection provision is
mandatory and the design approach is by far more realistic, since it
considers the P-Delta effect of the vertical loads.

Javier Encinas
ASDIP Structural Software
www.asdipsoft.com

----- Original Message -----
From: Paul Feather <pfeather(--nospam--at)san.rr.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, June 29, 2001 10:40 PM
Subject: Re: Half-allowable stresses for masonry


> The 1/2 allowable stresses apply to the masonry stresses only, not the
steel
> stresses.  This is covered in detail in the book "Reinforced Masonry
Design"
> by Schneider and Dickey, from development of the original 1/2 stress
concept
> to the current code provisions.  The use of 1/2 stresses should be applied
> judiciously.  The intent was for lightly loaded (i.e. "short" for seismic)
> low stress conditions primarily governed by the minimum steel
requirements.
> Often today the 1/2 stresses are utilized in situations where they are not
> truly appropriate in an effort to avoid the special inspection
requirements.
> This can be undesirable, because trying to bring a more highly loaded wall
> into a state where 1/2 stresses are permissible can result in over
> reinforcing when Fb is the parameter controlling As.  The result is a
> brittle failure mode controlled by the masonry rather than a ductile
failure
> mode controlled by the reinforcement.  According to the evolution of the
1/2
> stress provisions provided by S&D, a large contributing factor to this is
> the fact that Em is not reduced to be consistent, and therefore using 2n
> instead of n.
>
> Paul Feather
> ----- Original Message -----
> From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
> To: "SeaInt Listserver (E-mail)" <seaint(--nospam--at)seaint.org>
> Sent: Friday, June 29, 2001 4:04 PM
> Subject: Half-allowable stresses for masonry
>
>
> > When special inspection is not provided for masonry construction, the
UBC
> > (1994 & 1997) requires that "the allowable stresses for masonry in
Section
> > 2107 shall be reduced by one-half". Does this 50% reduction apply to
> > allowable steel stress as given in Section 2107.2.11? Or does it only
> apply
> > to allowable stresses related to f'm? In the equations for reinforced
> > masonry columns (Section 2107.2.5 in 1997 UBC), does the 50% reduction
> only
> > apply to the portion of the equation related to f'm and not to Fsc?
> >
> > This sentence is rather vague, as these articles within Section 2107
> > relating to allowable steel stress could be interpreted as being part of
> > "allowable stress design for masonry"; however, it seems that it is more
> > often interpreted to only apply to the masonry materials. Is there a
code
> > basis for not applying the 50% reduction to the allowable steel stress
> other
> > than interpretation of the word "masonry"?
> >
> >
> > William C. Sherman, PE
> > Camp Dresser & McKee, Inc.
> > Denver, CO
> > Phone: 303-298-1311
> > Fax: 303-293-8236
> > email: shermanwc(--nospam--at)cdm.com
> >
> >
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