Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

Downloaded From : www.EasyEngineering.net
CHAPTER 8
Forms for Footings
ww.EasyEngineering.n
General Information
In this book, concrete footings and foundations are defined as those
components of structures, relatively low in height, whose primary
functions are to support structures and equipment. In general, they
include:
1. Wall footings and low foundation walls
2. Column footings
3. Footings for bridge piers
4. Foundations for equipment
Footings usually are of considerable length, including those that
extend around a building, plus those that extend across a building.
They are constructed in excavated ground trenches. If the earth adjacent
to the footing is sufficiently firm, a trench can be excavated to the
desired width, and the earth can serve as the side form.
The pressure, which will vary from zero at the top of the forms to
a maximum value at the bottom, may be determined as discussed in
Chapter 3. Because the forms are filled rapidly, within an hour or less,
the maximum pressure will be 150 lb per sq ft times the depth in
feet.
The forces which the forms must resist are the lateral pressure
from the concrete plus any uplift pressure that may result where the
footings are constructed with sloping or battered sides and tops.
Because the depth of concrete usually is small, the pressure on the
forms will be relatively low. Materials used for forms include lumber,
plywood, hardboard, steel, and fiber tubes.
Forms for Foundation Walls
Foundation walls are constructed on and along wall footings, as illustrated
in Figure 8-1. Because of their low heights, usually varying
from 2 to 6 ft, the pressure on the forms will be less than that on forms
Downloaded From : www.EasyEngineering.net
197