Page 403 - Design of Reinforced Masonry Structures

6.54 CHAPTER SIX

Example 6.5 illustrates T-beam analysis of a masonry wall section built from nominal 8 ×
8 × 16 in. concrete masonry units, which is subjected to out-of-plane loads.

6.7.7 MSJC-08 Provisions for Design of Masonry Walls for
Out-of-Plane Loads
MSJC-08 Section 3.3.5.3 presents two different conditions for strength design of walls,
although the design procedure under both conditions is identical:

1. When the axial stress due to factored loads is less than or equal to 0.20 ′ f .
m
2. When the slenderness ratio exceeds 30 (i.e., h/t > 30), the axial stress due to factored
loads is required to be less than 0.05 ′ f .
m
The minimum required thickness of walls is 6 in. nominal. The design procedure sug-
gested by the MSJC Code is as follows:
1. The design strength should satisfy the following condition [Eq. (6.17), MSJC-08/3-27]:

M ≤ f M (6.17, MSJC-08/3-27)
u n
where f = 0.9 is the strength reduction factor.

2. Calculate the nominal moment strength from Eq. (6.18):
a ⎞
M = ( A f + P ⎜ ) ⎛ d − ⎟ (6.18, MSJC-08/3-28)
n s y u ⎝ ⎠ 2
where
P + A f
a = u s y (6.19, MSJC-08/3-29)
008 fb ′
.
m
The quantity in the numerator of Eq. (6.18) may be considered as effective area of rein-
forcement given by Eq. (6.20):
P + A f
A = u s y (6.20)
se
f y

3. The nominal shear strength of the wall should be determined as discussed in Chap. 4.
4. The horizontal midheight deflection d , due to service lateral loads and service axial loads
s
(without load factors), should be limited to value given by relationship in Eq. (6.21):
d ≤ 0.007h (6.21, MSJC-08/3-30)
s
5. The midheight deflection (assuming that simple-support end conditions apply) is to be
calculated from Eqs. (6.22) or (6.23) as applicable: