TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
FsAsjd
Mrs '
(ft&lb)
(eq 5-19)
12
And,
Fmkjbd 2
ts
1&
(ft&lb)
Mrm '
(eq 5-20)
12
2kTd
c. Design for axial compression.
(1) When determining the capacity of a masonry wall element in compression, the compression
reinforcement in the element will be neglected since its contribution is not significant. Only tied compression
reinforcement, such as in a column or pilaster will be considered effective. The axial stress in a masonry wall,
fa, is found as follows:
P
fa '
(psi)
(eq 5-21)
Ae
Where:
P = The axial load, lbs.
Ae = The area of the element effective in compression as shown in figure 5-2a and obtained from
table 5-3, in2.
(2) The design of columns in axial compression is given in chapter 9.
d. Design for shear.
(1) For shear design in masonry walls subjected to out-of-plane loading, the shear stress in a masonry
element, fv, is found as follows:
V
fv '
(eq 5-22)
bwd
Where:
V = The shear load, lbs.
bw = The width of the masonry element effective in resisting out-of-plane shear as shown in figure
5-2c and given in table 5-1, inches.
d = The depth of the masonry element effective in resisting the shear is shown in figure 5-2c and
given in table 5-1, inches. For one bar per cell, d = d1, and for two bars per cell, d = d2.
(2) For shear design in masonry walls subject to in-plane loading (shear walls) the shear stress in a
masonry element is found as follows:
V
fv '
(eq 5-23)
Ae
Where:
V = The shear load, lbs.
Ae = The area masonry element effective in resisting in-plane shear as shown in figure 5-2a and
obtained from table 5-3, inches.
5-5. Allowable working stresses. The allowable working stresses for masonry, Fm, (CMU and brick) are
given in table 5-7. These allowables are based on the masonry compressive strength, f'm, which either have
been assumed or have been determined from prism tests. The assumed f'm values, 1500 psi for solid units and
1350 psi for hollow units, are for type M and type S mortars. If type N mortar is used, f'm will be assumed
to be 1000 psi for all units. The assumed f'm values are reasonable and conservative in that they are in the
range a to of the prism strength. If the designer needs to use higher masonry strengths than the assumed
values, prism tests may be required. Generally reinforced masonry will be designed and detailed in
conformance with the assumed values given in table 5-7.
5-8
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