Rectangular Cross Section
The most commonly used cross section in the design of formwork is the rectangular cross section with breadth b and depth d (Figure 3.2). These are usually measured in the units of inches or millimeters.
For rectangular cross section, the formulas discussed in the previous section take the forms:
Moments of intertia: Ixx = , in.4 or mm4
db3 4 4
= , in.4 or mm4
c Iyy db2. 3 3 b
by* = — = —, in.3 or mm3 here c = –
The section properties for selected standard sizes of board, dimension lumber, and timbers are given in Table 3.1. The values given in this table can be used to calculate the properties given above. Table 3.2 provides section properties of standard dressed (S4S) sawn lumber.