Substituting gives 
G,!=. — x 4.62 + -I x 1.20 - ^(1.29 — 0.31) = 9.24 tons, 
allowing that when the britlgo is empty the stress on the ond lower lateral strut is 
greater than wlicu the span is covered by the moving load. The reader must not 
conclude that such is the case for all spans, as it is probable that the reverse would 
be true for spans exceeding two hundred and thirty or two hundred and forty feet. 
Next let us ascertain the stresses in the vertical sway bracing. 
Using the notation of Chapter IX. we can obtain the following data 
P' = I x 25 x 1 x 50 x -rj— = 0.313 ton 
2 2000 
F = な 』 1 -- ~ = 0.945 - 0.156 = 0.789 ton 
b = 15.4 
= 25 
/ = 10 
sec^ = -iiAM£±Wli = = li83G 
The stress in the vibration rod is therefore 
V sec 6 
2x25 (0.789 + 0.818) — 2x0.313x10 
15.4 
x 1.836 
5.824 
The stress in the intermediate strut is 
(7 = ~ (0.789 + 0.31 3) 一 0.313 = 2.442 tons. 
For the portal bracing 
F'= i x 32.6 x 1 x 50 x — = 0.408 ton 
2 2000 
P = 31 x ■ 9 ^. r 2 . 1 -1^- = 3.308 - 0.204 = 3.104 tons 
2 200U 2 
90x21 
201 ) 1 ) 
0.945 
b — 15.4 
d = 32.6 
/ = 13 
sec 6 == 
[0” + (l2 が 
13 
17.7 
18 
= 1.30 
氺 
The stress in one pair of vibration rods is therefore 
_ 2 x 32.6 (8.104 + 0.40S) ― 2 x 0.408 x 1 8 
丄— 一 151 
x 1.36 
It is evident that this method of obtaining sec is approximate. 
