Building Design and Construction Handbook - Merritt - Ventech!

9.132 SECTION NINE
Reinforcement required for flexure of shear walls as a cantilever should be proportioned
as for deep beams (Art. 9.88). Shear reinforcement is usually furnished
as a combination of horizontal and vertical bars distributed evenly in each story
(for increment of load). For low shear (where the factored shear force V u at a section
is less than 0.5�V c, where V c is the nominal shear permitted on the concrete), the
minimum shear reinforcement required and its location in a wall are the same as
for bearing walls (Art. 9.68). Maximum spacing of horizontal shear reinforcement,
however, should not exceed L w/5, 3h, or 18 in, where L w is the horizontal length
of wall and h the overall wall thickness (Fig. 9.56). Maximum spacing of the
vertical reinforcement should not exceed L w/3, 3h, or18in.
A thickness of at least L w/25 is advisable for walls with high shear.
The factored horizontal shear force V u acting on a section through the shear wall
must not exceed the nominal shear strength V n multiplied by � � 0.85.
V � (�V � �V � �V ) (9.110)
u n c s
where V c � nominal shear strength of the concrete and V s � nominal shear strength
provided by reinforcement. The horizontal shear strength at any section should not
be taken larger than
V � 10 �ƒ� hd (9.111)
n c
where ƒ�c � specified concrete compressive strength, psi
d � effective depth of wall, but not to be taken larger than 80% of the wall
length
h � wall thickness
Shear carried by the concrete should not exceed the smaller of the values of V c
computed from Eq. (9.112) or (9.113).
Nd u
4Lw V � 3.3 �ƒ� hd � (9.112)
c c
where N u � factored vertical axial load on wall acting with V u, including tension
due to shrinkage and creep (positive for compression, negative for tension).
� �
L w(1.25 �ƒ�c � 0.2N u/Lwh) Vc � 0.6 �ƒ� c � hd (9.113)
M /V � L /2
u u w
where Mu � factored moment at section where Vu acts.
Alternatively, Vc � 2 �ƒ�c hd may be used if Nu causes compression. Shear
strength Vc computed for a section at a height above the base equal to Lw/2 or onehalf
the wall height, whichever is smaller, may be used for all lower sections.
When Vu � 0.5�Vc, the area of horizontal shear reinforcement within a distance
s2 required for shear is given by
(V u/��V s)s2 Ah � � 0.0025hs 2
(9.114)
ƒ d
y
where s 2 � spacing of horizontal reinforcement (max � L w/5 � 3h � 18 in) and
ƒ y � yield strength of the reinforcement.
Also, when V u � 0.5�V c, the area of vertical shear reinforcement with spacing
s should be at least