Increase In Strength Of Several Woods By Seas0ning

Ash........44.7 per cent.

Beech.....61.9 "

Elm......12.3 per cent.

Oak.....28.1 "

White pine....9 per cent.

* With 840 lbs. the deflection was 1 inch, and the elasticity of the metal destroyed.

Brick-Work

A brick arch, having a rise of 2 feet, and a span of 15 feet 9 inches, and 2 feet in width, with a depth at its crown of 4 inches, bore 358,400 lbs. laid along its centre.

When The Breadth Or Depth Is Required

Rule

Divide the product obtained by the preceding rules by the square of the depth, and the quotient is the breadth; or by the breadth, and the square root of the quotient is the depth.

Illustration

If 128 is the product, and the depth is 8: then 128 / 82 =2, the breadth. Also, 123 / 2=64, and √64=8, the depth.

When A Beam Or Bar Is Supported At Both Ends, And Loaded In The Middle

Rule

Multiply the value of the ma. terial by 4 times the breadth and the square of the depth in inches, and divide the product by the length in feet.

Note

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

Example

What weight will a cast-iron bar, 5 feet between the supports, and 2 ins. square, bear in the middle, without permanent in-jury?

225X2X4X22=7200. which,+5=-1440 lbs.

Or, If The Dimensions Are Required To Support A Given Weight

Rule

Divide the product of the weight and length in feet by 8 times the value of the material, and the quotient will give the product of the breadth, and the square of the depth.

When The Weight Is In The Middle Between The Supports

Rule

Multiply the value of the material by the length in feet, and the breadth, and the square of the depth in inches, and divide the product by the product of the distances of the weight, or stress from either support.

Example

What weight will a cast-iron bar, 2 ins. square and 5 feet in length support without permanent Injury, at a distance of 2 feet from one end, or support?

225X5X2X22 9000

--------------=-=1500 lbs.

2x(5-2) 6

Floor Beams, Girders, Etc

The condition of the stress borne by a floor beam is that of a beam supported at both ends and uniformly loaded; but from the irregularity in its loading and unloading, and from the necessity of its possessing great rigidity, it is impracticable to estimate its capacity other than as a beam having the weight borne upon the middle of its length.

Wind-Mills. - (Molesworth.). To Compute The Angles Of The Sails

18 d2

23°---------= angle of the sall with the plane of motion at any part of r2 the sall; r representing radius of sail in feet, and d distance of any part of the sail lron the axis.