Page 229 - Design of Reinforced Masonry Structures

4.92 CHAPTER FOUR

The wall contains four openings to be spanned by lintels, which are located at dif-
ferent levels measured from the floor. For the two side openings, the roof dead and live
loads are transferred to lintels at a height of 12 ft from the floor; the total height of the
wall above these two openings is 8 ft. Similarly, the total wall depth over the two middle
openings is 12 ft. Separate checks will be made in each of these two cases to determine if
the lintels over these opening qualify for the arching action, and the loads that the lintels
must carry will be calculated accordingly.

Apex level of 45° triangle
Top of wall

Roof line

45° Top of opening 45°
Clear span, L = 20' 10'-4"
8'-0"
Le = 20'-8" 5'-3"
12' to floor

FIGURE E4.26B

a. Left opening (Fig. E4.26B)
Clear span (width of opening),
L = 20 ft
Length of bearings on each side of the opening = 8 in. (assumed).
Effective span,
L = center-to-center of bearings = 20 + 8/12 = 20.67 ft.
e
Assume overall depth of lintel,
h = 16 in. = 1.33 ft
Height of masonry above the lintel to the top of wall = 20 − 12 − 1.33 = 6.67 ft.
Minimum height of wall required above the lintel for arching action to exist =

½ (20.67) + 8/12 = 11 ft. This is less than the wall height above the lintel (= 6.67 ft).
Hence, the arching action cannot be assumed to exist, and the lintel must be designed to
carry all loads based on the tributary width basis.
The dead weight of the fully grouted masonry wall (nominal 8 in. wide, medium
2
3
weight units, grout weight = 140 lb/ft ) is estimated as 78 lb/ft of the wall area
(Table A.19). Therefore, the dead load is calculated as follows:
Dead load due to the 8 ft high wall (including lintel) = 8(78) = 624 lb/ft length of
lintel
Roof dead load = (12) (10) = 120 lb/ft
Total dead load on lintel, D = 624 + 120 = 744 lb/ft
Live load from the roof, L = (20) (10) = 200 lb/ft length of lintel
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