TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
CHAPTER 6
REINFORCED MASONRY WALLS
6-1. Introduction. This chapter covers the design of reinforced masonry walls by the working stress method
for lateral out-of-plane loads and axial loads. The design of reinforced masonry walls for in-plane lateral loads
(shear walls) and axial loads is covered in chapter 7. General design criteria, section properties, and allowable
stresses used but not contained herein are covered in chapter 5.
6-2. Design loadings.
a. Lateral loads. Lateral out-of-plane loads on masonry walls are determined from wind forces as given
in TM 5-809-1/AFM 88-3, Chapter 1 or from seismic forces as given in TM 5-809-10/NAVFAC P-355/AFM
88-3, Chapter 13.
b. Axial loads. Vertical in-plane compression or tension loads on masonry walls are determined from dead,
live, snow, and wind uplift forces as given in TM 5-809-1/AFM 88-3, Chapter 1.
6-3. Structural behavior.
a. Lateral loads. Most masonry walls are designed to span vertically and transfer the lateral loads to the
roof, floor or foundation. Normally, the walls are designed as simple beams spanning between structural
supports. Simple beam action is assumed even though reinforcement, which is needed to control horizontal
flexural cracking at the floor levels or to provide connectivity, may be present and will provide at least partial
continuity. Under certain circumstances, such as when a system of pilasters is present, the masonry walls may
be designed to span horizontally between pilasters which in turn span vertically to transfer the lateral loads
to the horizontal structural support elements above and below.
b. Axial loads. Loads enter the wall from roofs, floors, or beams and are transferred axially to the
foundation. When the resultant axial force is tension from wind uplift loadings, mortar tension will not be
used to resist these uplift forces. Instead, adequate reinforcement will be provided to anchor the top of wall
bond beam to the remainder of the wall and on down to the foundation. If the resultant of the vertical loads
which are applied to the wall at any level is not at the center of the wall; that is, it is not concentric; due
allowance will be made for the effects of eccentric loading. This includes any moments that are due to
eccentric loading as well as any additional moments caused by the rotation of floor or roof elements that
frame into the wall.
(1) Uniform loads. Uniform loads enter the wall as line loads, stressing the wall uniformly along its
length.
(2) Concentrated loads. When concentrated loads are not supported by structural elements, such as
pilasters, they may be distributed over a length of wall equal to the width of bearing plus four times the wall
thickness, but not to exceed the center to center distance between concentrated loads. Concentrated loads
will not be distributed across control joints.
c. Combined loads. The combined effects of lateral and axial loads may be assumed to act according to
the straight-line interaction equations given in this chapter or may be combined by other methods which are
based on accepted principles of mechanics.
6-4. Wall design equations. The equations in this paragraph may be used for the design of walls subjected
to bending and axial loads. Lateral (wind or seismic) loading will be applied inward and outward on all
exterior walls. Both the condition where the moment due to wind loading and the moment due to axial load
eccentricity are additive and the condition where they are not additive are shown on figures 6-1 and 6-2,
respectively.
a. Bending equations. The horizontal reaction at the bottom of the wall due to the combined effects of
eccentric and lateral loads is "Ra" and is determined as follows:
Pe
wh
Ra '
(lb/ft of wall)
(eq 6-1)
2
12h
Where:
P = The axial load, pounds per foot of wall length.
e = the distance from the centerline of the wall to the load P, inches.
h = The height of the wall, feet.
w = The lateral load on the wall, psf.
Note:
The "" in equation 6-1 refers to the two conditions; (1) where the eccentric and lateral loads are additive, and (2) where the eccentric and lateral loads are
not additive. Both conditions will occur on all exterior walls.
6-1
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