Page 519 - Design of Reinforced Masonry Structures

SHEAR WALLS 7.81

4. Most severe torsional shears: To account for the effects of torsional irregularity,
ASCE 7-05 Section 12.8.4.3 requires that accidental torsional moment, Ve , be
acc
multiplied by the torsional amplification factor, A .
x
The most severe total torsional shears result from the use of torsional moment
equal to V(e – A e ) for Wall A (minus sign is used for A e because this force
acc
x
x
acc
acts opposite to the direct shear V D,A ), and V(e + A e ) (plus sign is used for
x
acc
A e because this force acts with the direct shear V D,B ) for wall B. Thus,
acc
x
−
Ve ( − A e )( x )( R ) 150 (24 1 .52 4 8 )(
×
. )(224 600)
V TA = X acc R A = = 20 88 kips
.
,
,
,
J 1 728 000
×
+
( + A e ))(96 − x
Ve )(R ) 150 (24 1 .52 4 8 )(200 )
. )(72
V , TB = X acc R B = = 39 12 kips
.
J , 17228 000,
5. Total shear (Fig. E7.14B)
−
=
V ′ = V − V = 1125 2088 9162 kips
.
.
.
,
,
A D A T A

=
+
.
.
.
V B ′ = V D B + + V TB = 375 3912 7662 kips
,
,
Commentary:
1. To get an overall understanding of the influence of torsional moment, it is noted
that total lateral force to be resisted by walls A and B equals 91.62 + 76.62 =
168.24 kips versus applied lateral force of 150 kips.
2. The torsional moment also introduces shear force in walls C and D, but they are
not considered in this example as these walls are perpendicular to the applied
shear force and do not participate in resisting the applied shear force.
7.10 DESIGN CONSIDERATIONS
FOR SHEAR WALLS
7.10.1 Types of Reinforced Masonry Shear Walls
Masonry shear walls may be unreinforced or reinforced. As mentioned in previous chap-
ters, use of Type N mortar or masonry cement mortar is prohibited in Seismic Design
Category (SDC) D, E, and F structures (no such restriction for SFRS in other seismic
design categories).
Based on MSJC-05 Code, 2006 IBC (Section 2106) defined five types of masonry

shear walls (including both unreinforced and reinforced) for purposes of seismic design
as follows:
1. Ordinary plain (or unreinforced) masonry shear walls
2. Detailed plain masonry shear walls
3. Ordinary reinforced masonry walls
4. Intermediate reinforced masonry walls
5. Special reinforced masonry walls
These shear walls can be used as parts of SFRS in buildings as noted in Table 7.5. The
MSJC-08 Code introduced a few more types (a total of 12, including the above 5 types) of