TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
w = The lintel weight = 62 lb/ft
w' = The unit weight of the masonry triangle (assume no reinforced filled cells) = 50 psf
(b) Determine the area of reinforcement, Asb, required to provide a balanced steel ratio, Pe.
Asb = (Pe)(b)(d)
Pe=0.0027 (See table 5-9)
b = The lintel width = 7.62 in
d = The effective depth of lintel = 4.62 in
Asb = 0.0027(7.62)(4.62) = 0.095 in2
(c) The minimum reinforcement required above any wall opening is 1-#4 bar, As= 0.20 in2.
As = 0.20 in2 > Asb = 0.095 in2 therefore; the design section (shown in figure 8-3) is over-reinforced and the
compressive stress in masonry will control over the tensile stress in the reinforcement.
(d) The masonry resisting moment, Mrm, is determined as follows:
k = [(21.5 0.00568)2 2(21.5 0.00568)]
- (21.5 x 0.00568) = 0.387
j = 1 - k/3 = 1 - (0.387/3) = 0.871
Mmax = 257 ft-lb < Mrm = 1028 ft-lb
(a) Determine the moment that causes flexural cracking
of the lintel
section, Mcr, as follows: