Simplified Design for Structural Walls - Simplified Design of Reinforced Concrete Buildings - page 202

6.5 DESIGN FOR FLEXURE

For buildings of moderate height, walls with uniform cross-sections and uniformly distributed vertical and
horizontal reinforcement are usually the most economical. Concentration of reinforcement at the extreme ends of
a wall (or wall segment) is usually not required except in high and moderate seismic zones. Uniform distribution
of the vertical wall reinforcement required for shear will usually provide adequate moment strength as well.
Minimum amounts of reinforcement will usually be sufficient for both shear and moment requirements.

In general, walls that are subjected to axial load or combined flexure and axial load need to be designed
as compression members according to the provisions given in ACI Chapter 10 (also see Chapter 5)*. For
rectangular shearwalls containing uniformly distributed vertical reinforcement and subjected to an axial load
smaller than that producing balanced failure, the following approximate equation can be used to determine the
nominal moment capacity of the wall 6.1 (see Fig. 6-4):

⎡ ⎤

⎛ ⎞

⎛
⎜

⎞
⎟

P u
A st f y

c
w

⎜ ⎟ 1

φ M n =φ 0.5A st f y w 1 + −

⎢
⎢

⎥
⎥

⎝ ⎠

⎣ ⎦

where A st = total area of vertical reinforcement, in. 2
˜ w = horizontal length of wall, in.
P u = factored axial compressive load, kips
f y = yield strength of reinforcement = 60 ksi

A st

Figure 6-4 Plan View of Shearwall for Approximate Nominal Moment Capacity

* In particular, ACI 10.2, 10.10, and 10.12 are applicable for walls.