26 d

[TeX: $a = \frac{6 WL}{26 d}$]

The general proportions of his girders are as follows:

Length, 16
Height, 1
Area Top Flange, 1.0
Area Bottom Flange, 6.1

In the above formula for cast iron beams,

W = weight in tons.
a = area in square inches of bottom flange.
d = depth in inches.
h = length in inches.

The web uniting the two flanges must be made solid--as any opening, by
causing irregularity in cooling, would seriously affect the strength
of the beam.

_Example._--Required the dimensions of a Hodgkinson girder--for a span
of 60 feet--with a load of 10 tons in the centre.

6 x 10 x 60 x 12
a = ---------------- = 37 inches nearly.
60 x 12
26 x -------
16