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

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Properties of Form Material 43
of Commerce Voluntary Product Standard PS 20-70 (American Softwood
Lumber Standard). All information and calculations appearing
in this book are based on using lumber whose actual sizes are given
in Table 4-1 for dry lumber. Dry lumber is defined as lumber that has
been seasoned to a moisture content of 19% or less. Green lumber is
defined as lumber having moisture content in excess of 19%. All calculations
involving the dimensions of lumber should be based on
using the actual sizes of lumber.
When calculations are made to determine certain properties of
lumber, definitions, terms, and symbols are used as follows:
Cross Section: A section taken through a member perpendicular to
its length, or longitudinal axis.
Neutral Axis: A line through a member (such as a beam or a column)
under flexural stress on which there is neither tension nor compression.
In Table 4-1, the neutral axis, designated as X-X or Y-Y, is at the middepth
of the member and perpendicular to the loading of the member.
Moment of Inertia (I): The moment of inertia of the cross section of
a beam is the sum of the products of each of its elementary areas
times the square of the distance from the neutral axis of the section to
the areas, multiplied by the square of their distance from the neutral
axis of the section.
Section Modulus (S): The section modulus of the cross section of a
beam is the moment of inertia of the section divided by the distance from
the neutral axis to the most distant, or extreme, fiber of the section.
Figure 4-1 shows the cross section of a rectangular beam. The
width and depth of the beam are denoted as b and d, respectively.
The following symbols and equations are generally used when
making calculations related to the cross sections of rectangular beams:
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A= cross-sectional area of a section
= bd, in. 2
b= width of beam face on which load or force is applied, in.
FIGURE 4-1 Symbols for cross section of rectangular beam.
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