When the Beam or Bar is fixed at One End, and loaded at the Other. - Rule. Multiply the safe-load given in the table by the breadth and the square of the depth in inches, and divide the product by the length in feet.*

If the Dimensions are required of a Beam or Bar, supported at one End to sustain a Given Weight at the Other End. - Rule. Divide the product of the weight and the length in feet by the safe-load given in the table, and the result is the square of the depth multiplied by the breadth or thickness: so by dividing this result by the breadth, and extracting the square root of the quotient, we have the depth in inches.

When a Beam or Bar is fixed at Both Ends, and loaded in the Middle. - Rule. Multiply the safe-load given in the table by G times the breadth, and by the square of the depth in inches, and divide the product by the length in feet.

If the Dimensions of a Beam or Bar are required to support a Given Weight in the Middle, between the Fixed Ends. - Rule. Divide the product of the weight and the length in feet bv 6 times the safe-load given in the table, and the quotient will be the square of the depth multiplied by the breadth or thickness in inches: so we divide this result by the breadth, and extract the square root of the quotient, which gives the depth; or, divide the result by the square of the depth, and the quotient is the breadth or thickness.

* When the beam is loaded uniformly throughout its length, the result must be doubled.

When a Beam or Bar is supported at Both Ends, and loaded in the Middle. - RULE. Multiply the safe-load given in the table by 4 times the breadth, and by the square of the depth in inches, and divide this product by the length in feet.*

If the Dimensions are required to support a Given Weight. - Rule. Divide the product of the weight and the length in feet by 4 times the safe-load given in the table; the result is the square of the depth multiplied by the breadth or thickness: so we divide this result by the breadth, and extract the square root, which gives the depth; or. divide the result by the square of the depth, and the quotient is the breadth or thickness in inches.

In all uses, such as in buildings and bridges, where the structure is exposed to sudden impulses, the load or stress to be sustained should not exceed from 1/5 to 1/6 of the breaking-weight of the material employed; but when the load is uniform, or the stress quiescent, it may be increased to 1/3 or 1/4 of the breaking-weight. In churches, buildings, etc., the weight to be provided for should be estimated at that which at any time may be placed thereon, or which at any time may bear upon any portion of their floors. Where the weight of people alone is to be provided for, an estimate of 175 pounds per square foot of floor-surface is sufficient to provide for the weight of flooring and the load upon it. The usual allowance for stores and factories is 280 pounds per square foot of floor-surface.

* When the beam is loaded uniformly throughout its length, the result must be doubled.

When a beam has four or more supports, its condition as regards a stress upon its middle is that of a beam fixed at both ends.

I Wrought-Iron Beams.* (Tuentox Iron Works, Cooper, Hewitt, & Co., New York.)

To find the Safe-load for any of the Above Beams for a Given Length, Weight to be uniformly distributed. - Rule. Divide the safe-load of the beam given in the table by the length in feet'.

Illustration. - What is the weight, uniformly distributed, that may be borne with safety by an iron beam 6 inches deep, web 5/16 thick, flanges 3 1/4 inches wide, and 10 feet long? We find the safe-load given in the above table to be 92,000 pounds, which, divided by ten, the length in feet, gives 9,200 pounds.

* Load uniformly distributed, beam resting upon two supports.