d. Load Per Linear Foot. When the total load per square foot of floor area is known, the load
per linear foot on the girder can easily be figured. Assume that the girder load area of the building
shown in Figure 1-12 is sliced into 1-foot lengths across the girder. Each slice represents the weight
supported by 1 foot of the girder. If the slice is divided into 1-foot units, each unit will represent 1
square foot of the total floor area. The load per linear foot of a girder is determined by multiplying the
number of units, 12, by the total load per square foot, 70 pounds. This gives you 840 pounds per linear
foot on the girder (12 x 70 = 840 pounds). Now you can take the 840 pounds per load per linear foot of
girder and use Table 1-1, page 1-6, to determine the girder size. If your number is not on the table,
Figure 1-12. Girder load per linear foot
e. Total Floor Load. Note in Figure 1-12 that the girder is off center. Remember that half of
the load is supported by the girder and half is supported by the foundation walls. Therefore, the joist
length to be supported on one side of the girder is 7 feet (half of 14 feet), and the other side is 5 feet
(half of 10 feet) for a total distance of 12 feet across the load area. Since each slice is 1 foot wide, it has
a total floor area of 12 square feet. Assume that the total floor load for each square foot is 70 pounds.
Multiply the length times the width (7 feet x 12 feet) to get the total square feet supported by the girder
(7 feet x 12 feet = 84 square feet).
1-7. Girder Material. Wooden girders are more common than steel girders in small frame buildings.
Solid timbers may be used, or girders may be built up by using two or more 2-inch planks. Built-up
girders warp less easily than solid wooden girders and are less likely to decay in the center.
a. Choice of Material. Regardless of whether the girder is built-up or solid, it should be of well-
seasoned material. For a specific total girder load and span, the size of the girder will vary according to
the kinds of wood used, since some woods are stronger than others.