—— 242 — 
this detail will be from six to eight pounds for single track bridges, and from ten to 
iifteen pounds for double track bridges, the smaller numbers being for short spans 
and the larger for long ones. 
It will bo noticed in the diagram that the floor beam stiffeners at the support 
are placed close together so as to take up the vertical reaction of the hangers trans- 
ferred by the auxiliary pin. The sectional area of these stiffeners should be about 
equal to that of the hangers. 
Since this treatise was written, the author lias prepared for the Institution 
Civil Engineers, Loudon, a paper entitled An Analysis of the Weights of Iron 
Dead Loads for Iron Pratt and Whipple Truss Railroad Bridges ”, the following 
deductions from which will be iound use fill to Japanese engineers. 
For loiiir single intersection deck trusses the economic depths are about one 
less than those for the corresponding through trusses : for short double intersection 1 
trusses they are about three feet less, and for long double intersection trusses abo^t 
one foot less. 
The ratios of the total weights of iron per lineal foot for single track deck ⑽ ユ 
through bridges, excluding the weight of the iron bents over the piers and abutments, a 1，e 
[riven in the following table. 
Span. * 
Ratio. 
Span. 
Ratio. 
6o f 
0.88 
i8o f 
S.I 
1.01 
8o, 
0.94 
1 8c/ 
B.I 
1.08 
1 。。， 
1.00 
l<)O f 
0.1 
1.01 
150' 
1.05 
200 r 
D.I 
1.07 
160^ 
1.04 
250 ， 
1.05 
170 ， 
1.02 
30 o' 
1.05 
Tlio ratio o.' total weights of iron per lineal foot for double and single trft c ^ 
through bridges are as given in the following table. 
Span. 
Ratio. 
Span. 
Ratio. 
6c/ 
2.00 
18 。， 1).1 
I.Q-2 
Sc/ 
2.00 
20 C , 
1.87 
I00 r 
1.94 
24 O' 
1.25 
15c/ 
1.91 
280^ 
1.83 
1 8c' S.I 
1.90 
50V 
1.82 
The ratio of total weights of iron per lineal foot for double and single trac 、 
(lech bridges, when the weights of the iron bents over the piers and abutments a/ß ^ 
considered are as given in the following table. 
Span. I Ratio. 
Span. 
Ratio. 
60’ 1.99 
180^ D.I 
1. 7 斗 
80' 1.92 
20 O r 
1.74 
I。。' 1.83 
24c/ 
1.74 
J40, I 1.76 
280^ 
1.74 
180* S.I 1.76 
300' 
1.73 
