Page 234 - Design of Reinforced Masonry Structures

DESIGN OF REINFORCED MASONRY BEAMS 4.97

2'-8"

Lintel 4'-8"

Opening 4'-0"

5'-4" (Clear)
4'-0"

FIGURE E4.27A Design of a lintel.

a. Analysis of loads on lintel
Calculate the depth of lintel adequate to carry shear without shear reinforcement.
Clear span (width of opening),
L = 5 ft 4 in. = 5.33 ft
Length of bearings on each side of lintel = 8 in. = 0.67 ft
Effective span,
L = 5.33 + 0.67 = 6 ft
e
Assume depth of lintel, d = 8 in. (to be revised later if necessary)
Height of parapet = 2 ft 8 in. = 2.67 ft
Height of masonry above the top of lintel = 4 + 2.67 = 6.67 ft
Height of wall required above the top of lintel to develop arching action =
L 2 e + 8 in. = 6 + 067 367 ft < 667 ft
=
.
.
.
2
Hence there is sufficient masonry wall depth above the lintel and arching action
can be assumed to exist. The superimposed concentrated loads are applied at a height
of 4 ft above the top of lintel, which is 4 in. (4 − 3.67 = 0.33 ft = 4 in.) above the apex
of the 45° traingle; therefore, these loads would disperse through arching action at an
angle of 60°.
Calculate the weight of masonry, W, contained in the 45° triangle with base equal to
2
6 ft (Fig. E4.27B). The unit weight of masonry is 78 lb/ft of wall (Table A.19). Thus,
1 1
W = wL = ( 78 6) 2 = 702 lb
2
(
)
4 e 4