Ultimate Strength of Reinforced Concrete Masonry Walls

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On the contrary, the ultimate moment capacity of the cell reinforcement
(vertical reinforcement) in a combined joint and cell reinforced masonry
construction utilizes the concrete strength to resist the compression
forces.  The method of calculating ultimate moment of the vertical
reinforcement is the same as that presented in the Section 5-1 and 5-2 of
NAVFAC P-397 which is similar to that presented in the American Concrete
Institute standard, Building Code Requirements for Reinforced Concrete.
(b) The ultimate shear stress in joint masonry walls is computed
by the formula:
EQUATION:
Vu = Vu/An
(127)
where,
vu = unit shear stress, psi
Vu = total applied design shear at db/2 from the
support, lb/in
An = net area of section, in2/in
In all cases, joint masonry walls, which are designed to resist blast
pressures, shall utilize shear reinforcement which shall be designed to
carry the total shear stress.  Shear reinforcement shall consist of; (1)
bars or stirrups perpendicular to the longitudinal reinforcement, (2)
longitudinal bars bent so that the axis or inclined portion of the bent bar
makes an angle of 45 degrees or more with the axis of the longitudinal
part of the bar; or (3) a combination of (1) and (2) above.  The area of the
shear reinforcement placed perpendicular to the flexural steel shall be
computed by the formula:
vubs
EQUATION:
Av =
(128)
[phi]fy
where,
Av
=
area of shear reinforcement, in2
b
=
unit width of wall, in
s
=
spacing between stirrups, in
fy
=
yield stress of the shear reinforcement, psi
[phi]
=
strength reduction factor equal to .85
When bent or inclined bars are used, the area of shear reinforcement shall
be calculated using:
Vubs
EQUATION:
Av =
(129)
[phi]fy (sin [alpha] + cos[alpha])
2.08-207