TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
CHAPTER 8
LINTELS
8-1. Introduction. A lintel is a horizontal beam supporting loads over an opening. This chapter covers the
design of reinforced masonry lintels. Reinforced masonry lintels must have all cores and other voids solidly
grouted. Precast reinforced concrete or structural steel lintels will be designed in accordance with ACI 318
and the AISC Steel Construction Manual, respectively, except the deflection limits contained in this chapter
will be followed. Torsion is not covered in this chapter. Where torsion is a major consideration, the designer
should consider precast reinforced concrete lintels with closed loop stirrups. The principles of this chapter
may be used for designing beams of reinforced masonry that are not lintels. Except as contained herein,
design criteria, section properties, material properties, design equations, and allowable stresses are contained
in chapter 5.
8-2. Loading. In addition to its own weight, a lintel may carry distributed loads from above, both from the
wall weight and from floor or roof framing. The lintel may also carry concentrated loads from the framing
members above.
a. Distributed loads. The shape of the loading diagram for the distributed loads to the lintel depends upon
whether arching action of the masonry above the opening can be assumed. When arching action occurs, the
lintel supports only the masonry that is contained within a triangle having sides which begin at the ends of
the lintel and slope upward and inward 45 degrees from the horizontal to converge at an apex above the
center of the lintel. See figure 8-1 for an illustration of this triangular lintel loading distribution. When the
lintel deflects into the opening over which it spans, the masonry above the triangle will arch over the lintel
and be supported by the more rigid walls on either side of the opening. For the arch to be stable, both ends
of the opening must have sufficient horizontal restraint to provide the confining thrust necessary to support
it laterally. Therefore, arching action should not be considered where the end of the arch and the lintel are
near a wall corner, near a control or building expansion joint, or in stacked bond walls. When arching action
can be assumed, the lintel will be designed to carry its own weight plus the weight of masonry within the
triangle above. Where uniform floor or roof loads are applied to the wall above the apex of the triangle, it
will be assumed that arching action will carry these loads around the opening and not load the lintel. When
uniform floor or roof loads are applied below the apex of the triangle, arching action cannot take place and
these loads will be carried downward and applied uniformly on the lintel. Also, when a uniform floor or roof
load is applied below the apex of the triangle, it will be assumed that all of the weight of the masonry above
the lintel is uniformly supported by the lintel.
b. Concentrated loads. Concentrated loads from beams, girders, or trusses framing into the masonry wall
above an opening will be distributed downward from the apex of a triangle which is located at the point of
load application. The sides of this triangle make an angle of 60 degrees with the horizontal. The load is
transferred as a uniform load over the base of the triangle. This uniform load may extend over only a portion
of the lintel. See figure 8-1 for an illustration of the distribution of concentrated loads on lintels.
8-3. Allowable deflection. For all lintels, the total deflection will be limited to L/600, not to exceed 0.3
inches.
8-4. Masonry lintel deflections.
a. Deflection parameters. When calculating lintel deflections the following parameters will be used.
(1) Span length. The assumed span for deflection calculations will be the distance between the centers
of supports, illustrated as dimension "L" on figure 8-1.
(2) Moment of Inertia. The moment of inertia for deflections will be the effective moment of inertia,
Ie, which will be determined as follows:
Ie = (Mcr/Mmax) 3Ig + [1 - (Mcr/Mmax) 3] Icr (in4)
(eq 8-1)
Where:
Mmax = The maximum moment in the member at the design load level, inch-pounds.
pounds.
8-1
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