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RE: CMU Wall Effective Flange Width
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: CMU Wall Effective Flange Width
- From: Michael Bryson <MBryson(--nospam--at)mhpse.com>
- Date: Tue, 11 Mar 2003 10:12:44 -0800
think the intent here is to treat the wall like you would a T-beam in reinforced
concrete with effective flanges. If your bar spacing is greater than 48" than
you would be limited to 48" for the effective flange width regardless of the
size or number of bars you put in one cell. For your example of two
reinforced cells at 6'-0" OC I would interpret the code to require you
to use an effective flange width of 36".
I'm analyzing a wall for
a 15' high, single story, 8" CMU, hip roof, residential structure
for out of plane bending under wind loads. Two (2) vertically reinforced
cells are located 6' on center. Would it be inappropriate
to assign an effective compression flange width of 56" (48" + 8") or even
72" rather than 48" (6*T)? While I would expect ACI 530 to
be pretty clear on this, it appears that the MDG uses this kind of
rationalization in assigning effective flange widths greater that
48" in the design of pilasters where 6*T is permitted on either side of
the pilaster. It appears that the a literal interpretation
would penalize the use of double reinforced cells spaced more than 48"
o.c.. The ACI 530-02 Sec. 18.104.22.168 further complicates the
matter by specifying the effective flange width "per bar" which would seem to
indicate that the effective flange width could be much larger than 48" for an
8" wall where two adjacent reinforced cells are used. In short, it
appears that if a bar is placed in two adjacent cells located 6' o.c. that 'b'
would be limited by 's' or 72" not '6T per bar'.
Christopher A. Banbury, PE
Nicholson Engineering Associates, Inc.
PO Box 12230,
Brooksville, FL 34603
7468 Horse Lake RD, Brooksville, FL 34601
(352) 754-9167 (f)