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

Re: Half-allowable stresses for masonry

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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
>
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   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
> ******* ****** ****** ****** ******* ****** ****** ********
>


******* ****** ******* ******** ******* ******* ******* ***
*   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 
******* ****** ****** ****** ******* ****** ****** ********