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

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CHAPTER 10
Forms for
Columns
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General Information
Concrete columns are usually one of five shapes: square, rectangular,
L-shaped, octagonal, or round. Forms for the first four shapes are generally
made of Plyform sheathing backed with either 2 × 4 or 2 × 6
vertical wood battens. Column clamps surround the column forms to
resist the concrete pressure acting on the sheathing. Forms for round
columns are usually patented forms fabricated of fiber tubes, plastic, or
steel. However, all shapes of columns can be made of fiberglass forms.
An analysis of the cost of providing forms, including materials,
labor for erecting and removing, and number of reuses, should be
made prior to selecting the materials to be used.
Pressure on Column Forms
Determining the lateral pressure of the freshly placed concrete against
the column forms is the first step in the design of column forms.
Because forms for columns are usually filled rapidly, frequently in
less than 60 minutes, the pressure on the sheathing will be high, especially
for tall columns.
As presented in Chapter 3, the American Concrete Institute recommends
that formwork be designed for its full hydrostatic lateral pressure
as given by the following equation:
P m
= wh (10-1)
where P m
is the lateral pressure in pounds per square foot, w is the
unit weight of newly placed concrete in pounds per cubic foot, and h
is the depth of the plastic concrete in feet. For concrete that is placed
rapidly, such as in columns, h should be taken as the full height of the
form. There are no maximum and minimum values given for the
pressure calculated from Eq. (10-1).
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