80 .434 972
90 .464 1039
100 .494 1106
120 .554 1241
140 .614 1375
150 .643 1440
160 .673 1507
170 .703 1575
180 .733 1642
200 .792 1774
225 .867 1942
250 .940 2105
275 1.013 2269
300 1.087 2435

The weight of a single track railway bridge may be taken as equal to
that of a double track highway bridge,--and the trusses that will be
large enough for one will be large enough for the other.

The greatest load that a highway bridge can be subjected to is 120
lbs. to the square foot of surface.

TABLE OF CAMBERS FOR BRIDGE TRUSSES.

Span. Camber. Span. Camber. Span. Camber. Span. Camber.
feet. Inches. Feet. Inches. Feet. Inches. Feet. Inches.

25 0.8 75 2.5 175 5.8 275 9.2
30 1.0 100 3.3 200 6.7 300 10.0
50 1.7 120 4.0 225 7.5 325 10.8
60 2.0 150 5.0 250 8.3 350 11.7

TRAUTWINE'S TABLE FOR FINDING INCREASE IN
LENGTH OF UPPER CHORD BEYOND THE
LOWER CHORD ON ACCOUNT OF THE CAMBER.

Multiply Multiply
Depth of Camber Depth of Camber
Truss. by Truss. by

1-4 span 2.00 1-12 span .666
1-5 " 1.60 1-13 " .614
1-6 " 1.33 1-14 " .571
1-7 " 1.15 1-15 " .533
1-8 " 1.00 1-16 " .500
1-9 " .888 1-17 " .470
1-10 " .800 1-18 " .444
1-11 " .727 1-20 " .400

TABLE OF AMERICAN WOODS.

Weight per Resistance in lbs. per
Kind. cubic foot square inch. Value of s.
in pounds. Extension Compression.

White Pine. 26 12,000 6000 1229
Yellow Pine. 31 12,000 6000 1185
Pitch Pine. 46 12,000 6000 1727
Red Pine. 35 12,000 6000 1527
Virginia Pine. 37 12,000 6000 1456
Spruce. 48 12,000 6000 1036
Tamarack. 26 12,000 6000 907
Canada Balsam. 34 12,000 6000 1123
White