Building Design and Construction Handbook - Merritt - Ventech!

9.106 SECTION NINE
The advantages of counterfort walls are the large effective depth for the cantilever
reinforcement and concrete efficiently concentrated in the counterfort. For
very tall walls, where an alternative cantilever wall would require greater thickness
and larger quantities of reinforcing steel and concrete, the savings in material will
exceed the additional cost of forming the counterforts. Accurate design is necessary
for economy in important projects involving large quantities of material and requires
refinement of the simple assumptions in the definition of counterfort walls. The
analysis becomes complex for determination of the division of the load between
one-way horizontal slab and vertical cantilever action.
See also Art. 6.7 (F. S. Merritt, ‘‘Standard Handbook for Civil Engineers,’’
McGraw-Hill Publishing Company, New York.)
9.72 RETAINING WALLS SUPPORTED ON FOUR
SIDES
For walls more than 10 in thick, the ACI 318 Building Code requires two-way
layers of bars in each face. Two-way slab design of this reinforcement is required
for economy in basement walls or subsurface tank walls supported as vertical spans
by the floor above and the footing below, and as horizontal spans by stiff pilasters,
interior cross walls, or end walls.
This type of two-way slab is outside the scope of the specific provisions in the
Code. Without an ‘‘exact’’ analysis, which is seldom justified because of the uncertainties
involved in the assumptions for stiffnesses and loads, a realistic design
can be based on the simple two-way slab design method of Appendix A, Method
2, of the 1963 ACI 318 Building Code.
FOUNDATIONS
Building foundations should distribute wall and column loads to the underlying soil
and rock within acceptable limits on resulting soil pressure and total and differential
settlement. Wall and column loads consist of live load, reduced in accordance with
the applicable general building code, and dead load, combined, when required, with
lateral loads of wind, earthquake, earth pressure, or liquid pressure. These loads
can be distributed to the soil near grade by concrete spread footings, or to the soil
at lower levels by concrete piles or drilled piers.
9.73 TYPES OF FOUNDATIONS
A wide variety of concrete foundations are used for buildings. Some of the most
common types are illustrated in Fig. 9.41.
Spread wall footings consist of a plain or reinforced slab wider than the wall,
extending the length of the wall (Fig. 9.41a). Plain- or reinforced-concrete individual-concrete
spread footings consist of simple, stepped, or sloped two-way concrete
slabs, square or rectangular in plan (Fig. 9.41b to d). For two columns close
together, or an exterior column close to the property line so that individual spread
or pile-cap footings cannot be placed concentrically, a reinforced-concrete, spread