TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
Shear Check.
(a) Determine the shear stress in the lintel, Fv, using the ACI shear coefficients as follows:
The shear stress at the face of the first interior support, fvi, is determined as follows:
Where:
V1 = The shear force at the first interior support, lb
= 1.l5wL/2= 1.15(934)(12)/2 = 6445 lb
The shear stress at the face of the exterior support, fv2,is determined as follows:
Where:
V2 = The shear force at the exterior support, lb
= wL/2 = (934)(12)/2 = 5604 lbs
Note. The shear stress at the first interior support governs the design.
So; fv = fv1 = 41.02 lb/in2
Fv= 1.0%f*m = %1350 lb/in2 = 36.7 lb/in2
(b) Determine the allowable shear stress, Fv, as follows:
fv =41.02 psi > Fv = 36.7 psi; Therefore, shear reinforcement is required in the beam at the interior support.
Since fv > 20 psi and there is required negative reinforcement, web reinforcement must be provided to carry
the entire shear for a distance of one-sixteenth the clear span beyond the point of inflection. The allowable
shear load based on 20 psi, Vallow, is:
Vallow = (20)(7.62)(20.62) = 3142 lb
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