Page 213 - Civil Engineering Formulas

148 CHAPTER FIVE

where M smaller of two end moments on column as determined by con-
1
ventional elastic frame analysis, with positive sign if column is bent in
single curvature and negative sign if column is bent in double curvature; and
M absolute value of larger of the two end moments on column as deter-
2
mined by conventional elastic frame analysis.
For columns not braced against sidesway, when
kl u
22 (5.110)
r

LOAD-BEARING WALLS
These are subject to axial compression loads in addition to their own weight
and, where there is eccentricity of load or lateral loads, to flexure. Load-bearing
walls may be designed in a manner similar to that for columns but including the
design requirements for non-load-bearing walls.
As an alternative, load-bearing walls may be designed by an empirical pro-
cedure given in the ACI Code when the eccentricity of the resulting compres-
sive load is equal to or less than one-sixth the thickness of the wall.
Load-bearing walls designed by either method should meet the minimum
reinforcing requirements for non-load-bearing walls.
In the empirical method the axial capacity, kip (kN), of the wall is
P n 0.55 f c A g (5.111)
2
kl c
1
32h
where f 28-day compressive strength of concrete, ksi (MPa)
c
2
2
A gross area of wall section, in (mm )
g
strength reduction factor 0.70
l vertical distance between supports, in (mm)
c
h overall thickness of wall, in (mm)
k effective-length factor
For a wall supporting a concentrated load, the length of wall effective for the
support of that concentrated load should be taken as the smaller of the distance
center to center between loads and the bearing width plus 4h.
SHEAR WALLS

Walls subject to horizontal shear forces in the plane of the wall should, in addi-
tion to satisfying flexural requirements, be capable of resisting the shear. The
nominal shear stress can be computed from

V u
v u (5.112)
hd