Civil Engineering Reference
In-Depth Information
in the stem is limited to a maximum value of approximately the stem
thickness required for moment will probably provide sufficient shear resistance without
using stirrups. Furthermore, it will probably be sufficiently thick to limit lateral deflec-
tions to reasonable values.
For heights up to about 12 ft, the stems of cantilever retaining walls are normally
made of constant thickness because the extra cost of setting the tapered formwork is usu-
ally not offset by the savings in concrete. Above 12-ft heights, concrete savings are usu-
ally sufficiently large to make tapering economical.
Actually, the sloping face of the wall can be either the front or the back, but if the
outside face is tapered it will tend to counteract somewhat the deflection and tilting of the
wall due to lateral pressures. A taper or batter of in. per foot of height is often recom-
mended to offset deflection or the forward tilting of the wall.
If
(0.18
f
c
/
f
y
),
1
4
Base Thickness
The final thickness of the base will be determined on the basis of shears and moments. For
estimating, however, its total thickness will probably fall somewhere between 7 and 10%
of the overall wall height. Minimum thicknesses of at least 10 to 12 in. are used.
Base Length
For preliminary estimates, the base length can be taken to be about 40 to 60% of the over-
all wall height. A little better estimate, however, can be made by using the method de-
scribed by the late Professor Ferguson in his reinforced concrete text.
4
For this discussion,
reference is made to Figure 13.13. In this figure,
W
is assumed to equal the weight of all
Figure 13.13
4
Ferguson, P. M., 1979,
Reinforced Concrete Fundamentals
, 4th ed. (New York: John Wiley & Sons), p. 256.
