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,

round up.

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).

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.

Integrated Publishing, Inc. |