Page 220 - Design of Reinforced Masonry Structures

4.84 CHAPTER FOUR

*
TABLE 4.8 Lintel Weights in Pounds per Linear Foot [4.13].
Wall thickness, in.
Lintel height,
in. (nominal) 4 6 8 10 12
Lightweight concrete masonry units
8 24 39 54 69 87
16 49 78 110 141 180
24 72 117 162 207 262
Normal weight concrete masonry units
8 29 45 61 77 94
16 58 90 122 155 197
24 87 135 183 231 282
* 3
Face shell mortar bedding. Listed weights are based on grout weight of 145 lb/ft and unit
3
3
weight of masonry units as 100 lb/ft for lightweight units and 145 lb/ for normal weight.
2. Dead load of wall above the lintel
If arching action is assumed to be present, the lintel should be designed to support the
sum of the dead weight of the masonry contained in a 45°-triangular area above the lin-
tel and the self-weight of the lintel (Fig. 4.22a). One may consider triangles formed by
45 to 60° over the effective lintel span to determine the wall tributary area whose weight
is to be carried by the lintel (45° shown in Fig. 4.22a). Obviously, the area contained
2
within a 60° triangle (i.e., an equilateral triangle, area A = 0.433L , L = base length) is
2
much larger than that contained within the 45° triangle (area A = 0.25L ). However, the
recommended practice is to use 45° triangles for computing the dead load from the wall
to be carried by the lintel [4.14]. In case of uncertainty regarding the presence of arching
action in the masonry above the lintel, or on both sides of the opening to form the arch,
the arching action should be disregarded, and the lintel should be designed for the full
load based on the tributary area basis.
Estimation of wall height above the top of lintel requires prior knowledge of the depth
of lintel which is unknown. For preliminary design, a nominal lintel depth of 8 in. (mini-
mum permissible depth for a concrete masonry beam) for short spans and larger depths
(16 or 24 in.) for longer spans may be assumed. These assumed depths may be revised
later as necessary for the final design.
For wall heights above the lintel equal to or less than half the effective span of lintel
plus 8 in., arching action, being ineffective, is ignored. In such cases, the lintel should

be designed to carry the dead weight of the entire rectangular portion of the wall over
the effective span (Fig. 4.22b).
3. Dead and live load from floor or roof
Dead and live load that may be transferred to a lintel might be (a) a uniform load or
(b) a concentrated load. Both types of loads may be determined as follows:
a. Uniform load
Uniform load occurs on a lintel, for example, when floor or roof sheathing is nailed
to a ledger beam, which is bolted to the wall directly supported over the opening as
shown in Fig. 4.24. The ledger beam, in turn, transfers the floor or the roof load to
the wall, which may have an opening. Two load cases may be considered. If the floor
or the roof line lies above a distance from the top of lintel equal to half the effective