The Locomotive - Lighthouse Survival Blog

1893] Tin: LOCOMOTIVE 137
Supervising Inspectors of Steam Vessels (as amended in January, 1892,) require that "no
braces or stays hereafter employed iu the construction of [marine] boilers shall be
allowed a greater strain than 6,000 pounds per square inch of section "; but, in the con-
struction of land boilers it is not usual to require such a large margin of safety as the
United States rule just quoted implies, and in land boilers the strain on braces will
nearly always run nearer to 7,500 lbs. per square inch than to 6,000 lbs. If we allow
7,500 lbs. as the safe working strain per square inch, we shall find that a round brace,
one inch in diameter, will safely bear 5,890 lbs. (7. 500 x. 7854—5,890.) From this it is
easy to calculate how many such braces a given boiler-head should have. Thus we see
from Table I that in a 60-inch boiler whose upper tubes are 28 inches below the shell,
the area to be braced is 930 square inches. If the boiler is to carry a pressure of 100 lbs.
to the square inch, the braces must -withstand a total strain of 930x100=93,000
pounds; and as each single brace of inch round iron will safely bear only 5,890 pounds,
-we find how many braces will be recjuired by dividing 93.000 lbs., the total load, by
5,890 lbs., the load that one brace can carry. We find that 93,000^5,890=15.8; so that
the proposed boiler will require 16 braces. We have performed this calculation for
every boiler included in Table I, and the results are contained in Table II, which gives
the requisite number of braces of one-inch round iron for boilers carrying 100 lbs. pressure.
As an example in the use of Table II. let us take the following : How many braces
of inch round iron are required to stay the head of a 72-inch boiler, the distance from
TABLE n. XL'^IBER OF BRACES REQUIRED, AT 100 LBS. PRESSUTIE.
Height
FROM Tube?
TO Sheix.