Walls - Design of Reinforced Concrete - page 554

5. The spacing of vertical and horizontal reinforcement may not exceed three times
the wall thickness, or 18 in. (14.3.5).
6. Reinforcing for walls more than 10 in. thick (not including basement walls) must
be placed in two layers as follows: one layer containing from one-half to two-
thirds of the total reinforcing placed in the exterior surface not less than 2 in. nor
more than one-third times the wall thickness from the exterior surface; the other
layer placed not less than in. nor more than one-third times the wall thickness
from the interior surface (14.3.4).
7. For walls less than 10 in. thick the Code does not specify two layers of steel, but
to control shrinkage it is probably a good practice to put one layer on the face of
walls exposed to view and one on the nonstressed side of foundation walls 10 ft
or more in height.
8. In addition to the reinforcing specified in the preceding paragraphs, at least two
#5 bars must be provided around all window and door openings. These bars must
be extended for full development lengths beyond the corners of the openings but
not less than 24 in. (14.3.7).
9. For cast-in-place walls, the area of reinforcing across the interface between a
wall and a footing must be no less than the minimum vertical wall reinforcing
given in paragraph 2 of this list (15.8.2.2).
10. For precast, nonprestressed walls, the reinforcement must be designed in accor-
dance with the preceding requirements on this list as well as the requirements of
Chapters 10 or 14 of the Code, except that the area of the horizontal and vertical
reinforcing must not be less than 0.001 times the gross cross-sectional area of the
wall. In addition, the spacing of the reinforcing may not be greater than five
times the wall thickness or 30 in. for interior walls, or 18 in. for exterior ones
(16.4.2).

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18.3 LOAD-BEARING CONCRETE WALLS—EMPIRICAL

DESIGN METHOD
Most of the concrete walls in buildings are load-bearing walls that support not only verti-
cal loads, but also some lateral moments. As a result of their considerable in-plane stiff-
nesses, they are quite important in resisting wind and earthquake forces.
Load-bearing walls with solid rectangular cross sections may be designed as were
columns subject to axial load and bending, or they may be designed by an empirical
method given in Section 14.5 of the Code. The empirical method may only be used if the
resultant of all the factored loads falls within the middle third of the wall (that is, the ec-
centricity must be equal to or less than one-sixth the thickness of the wall). Whichever of
the two methods is used, the design must meet the minimum requirements given in the pre-
ceding section of this chapter for non-load-bearing walls.
This section is devoted to the empirical design method, which is applicable to rela-
tively short vertical walls with approximately concentric loads. The Code (14.5.2) pro-
vides an empirical formula for calculating the design axial load strength of solid
rectangular cross-sectional walls with e less than one-sixth of wall thicknesses. Should