— 64 一 
Dead Loatl. 
Wind Pressure. 
The live load stresses in floor beams and track stringers and 
in all plate girders not exceeding twenty- five (25) feet m length are 
to be iucreasecl by twenty-five (25) per cent., in order to provide for 
shock. 
For the same reason the stresses in plate girders of and ex- 
ceeding twenty-five (25) feet in length are to be increased by the 
percentages given in the following table 
Span. 
Percentage. 
Span. 
Percentage. 
2$' and 26' 
24 
yf and 38' 
18 
27’ ，， 28 ， 
23 
39’ ， 40’ and 41' 
16 
29’ ，， 3 。’ 
4 ゲ ， 43 ' ，， 44 ’ 
H 
3 ヅ 3 ゲ 
ai 
45 ’ ， 46’ ，， 47 ’ 
12 
ll' » 
20 
4 か， 4 ゲ ，， 5 〇 ' 
10 
3 ダ ，， 36 ， 
T 9 
5i r to 6o f 
8 
The dead load is to include tlic weight of all tlie iron and wood 
in the structure, excepting those portions resting directly on the 
abutments, and whoso weights do not affoct the stresses in the 
trusses. 
Oak lumber is assumed to weigh four and a third (4|) and 
pine two and a half (2|) pounds per foot board measure. Should, 
in any bridge of or below two hundred (200) feet span, tlie calculated 
dead load differ more tlian seven (7) per cent., or in any bridge 
above two hundred (200) feet span more than four (4) per cent, 
from that assumed, tlie calculations of stresses &c. are to be made 
over with a new assumed dead load. 
Tlie -wind pressure is to bo divided into two parts, one a moving 
load of two hundred and forty (240) pounds per lineal foot and tlie 
other a fixed load of thirty (80) pounds per square foot of exposed 
bridge surface. Tlie latter is to be determined by adding together 
tliG area of tlie cloyatton of the floor system, figured by multiplying 
tlie vertical distance from the top of the rail to tlie bottom of the 
track stringer by the length of the span, and twice the area of the 
vertical projection of one truss. 
Trusses of less than two hundred (200) feet span are also to be 
proportioned for a pressure of fifty (50) pounds per square foot 
wlien unloaded, those of from two hundred (200) to two hundred 
and fifty (250) feet for forty-five (45) pounds per square foot, and 
