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

Downloaded From : www.EasyEngineering.net
CHAPTER 4
Properties of
Form Material
ww.EasyEngineering.n
General Information
Materials used for forms for concrete structures include lumber, plywood,
hardboard, fiberglass, plastics, fiber forms, corrugated boxes,
steel, aluminum, magnesium, and plaster of paris. Additional materials
include nails, bolts, screws, form ties, anchors, and other accessories.
Forms frequently involve the use of two or more materials, such as
plywood facing attached to steel frames, for wall panels.
Among the properties that form materials should possess are the
following:
1. Adequate strength
2. Adequate rigidity
3. Surface smoothness, where required
4. Economy, considering initial cost and number of reuses
Properties of Lumber
Lumber used for formwork that is finished on all sides is designated
as Surfaced-4-Sides (S4S) lumber. The cross-sectional dimensions of
lumber are designated by nominal sizes, but the actual dimensions
are less than the nominal dimensions. For example, a board designated
as a nominal size of 2 in. by 12 in. has an actual size of 1½ in. by
11¼ in. after it is surfaced on all sides and edges. Commercial lumber
is available in lengths that are multiples of 2 ft, with 18 ft as the common
maximum length of an individual board. Table 4-1 provides
the nominal and actual sizes for lumber that is commonly used for
formwork.
The dressed sizes and properties of lumber appearing in Table 4-1
conform to the dimensions of lumber set forth in the U.S. Department
Downloaded From : www.EasyEngineering.net
41