Page 340 - Design of Reinforced Masonry Structures

5.60 CHAPTER FIVE

each corner. Under flexure, the column behaves akin to a beam (oriented vertically), with
two corner bars near the column face acting in tension or compression (depending on the
direction of bending). A shear wall, on the other hand, acts as a deep beam; its reinforce-
ment configuration consists of several equal-diameter reinforcing bars oriented vertically
at equal intervals (at multiples of 8 in. in a wall constructed from 8 × 8 × 16 in. CMUs)
along the length of the wall, and all cells are grouted solid. Due to bending caused by in-
plane loads, some of those bars would be in tension and some in compression, depending
on their distances from the neutral axis of the cross section—this is where a shear wall is
different from a column. The forces in reinforcing bars calculated from strain distribution
as illustrated in Sections 5.7 and 5.8.

5.10 SHEAR STRENGTH OF MASONRY
COLUMNS

Shear strength of masonry columns depends on the shear span ratio, M /V d , and can
u v
u
be determined based on the same general principles as applied to beams (discussed in
Section 4.10). Calculations for shear strength of masonry columns differ from those for
beams because of the presence of axial load (beams are designed primarily as flexural
members, may have very small axial loads, the factored axial load not to exceed 0.05A f ′,
n m
MSJC Section 3.3.4.2.1). The nominal shear strength, V , of a reinforced masonry member
nm
is calculated as the sum of two component strengths: (1) nominal shear strength of masonry,
V and (2) the nominal shear strength provided by reinforcement (i.e., lateral ties), V :
m ns
V = V + V ns (4.97 repeated)
nm
n
where
⎡ ⎛ M ⎞ ⎤
⎢
V = 40 175. − . ⎜ u ⎟ ⎥ A f ′ + 025. P (4.91 repeated)
⎣ Vd ⎠ ⎦
nm ⎝ n m u
u
v
( A y )
V = 05 v fd (4.101 repeated)
.
ns v
s
The following limitations apply to the above three expressions:
1. The value of the shear span ratio, M /V d , in Eq. (4.91) is to be taken as positive number
u v
u
which need not be taken greater than 1.0.

2. The value of V in Eq. (4.97) is limited based on the shear span ratio, M /V d , as
n
u
u v
follows:
(a) Where M /V d ≤ 0.25,
u v
u
V ≤ 6 A f ′ (4.92 repeated)
n n m
(b) Where M /V d ≥ 1.0,
u u v
V ≤ 4 A f ′ (4.93 repeated)
n n m
(c) The maximum value of V for M /V d between 0.25 and 1.0 is to be determined from
n
u v
u
linear interpolation.