159 OF ENGINEERING FOKMULÆ.
Loads on Amebican Railway Bridges.
American Society Civil Engineers, June 1872
(Griffin and Clarke.)
In America it is sometimes the practice to double
the live load for the calculation of girder strains,
varying the stress per square inch in proportion
to the ratio of dead to live load.
Loads fkk Foot Run adopted kecently in America as
a Basis fob Calculating Gikdek Strains.
Span in Feet. Dead Load in Tons ; per Foot Run. Live Load X 2 Tons per Foot Run. Total Load in Tons per Foot Run.
From 0 to 12 ■22 4-46 4-68
12 „ 17 •25 3-5T 3'81
17 „ 25 '28 3-12 3'40
25 „ 50 1 -31 2’68 2-99
50 „ 83 •36 2'48, 2-74
100 I . ’40 2-23 2’63
110 •49 2-17 2-66
125 •51 2-11 2'62
150 •55 2'03 2'58
175 • 58 1-96 2’54
200 -67 1-90 2-57
226 -76 1-87 2-63
250 •89 1-85 2-U
3n0 1-07 1-81 2*88
350 1-34 1-78 3'12
400 1-79 1-78 3’57
To Find the Strain on Top ok Bottqm Booms of Gibders
of different Depth (Load distributed).
D = Depth of Girder. L = Load distributed.
S — Strain on top and bottom booms.
s 1 1 i | A vr A ä * * k
S=Lx ’75 •875 1 1-125 1'25 1-375 1-5 1-625 1-75 1’870 2 r ' i