THE NEBRASKA CITY BRIDGE.
9
IV.
SUPERSTRUCTURE.
The superstructure consists of two through spans and one deckspan. Each through span is 400 feet long between centers of endpins, and 50 ft, deep,, divided into 15 panels of 20 ft, 8 in. each, thetrusses being placed 22 feet between centers. The deck span is 325ft. long and 37 ft, deep, divided into 13 panels of 25 ft, each, thetrusses being placed 20 ft. between centers. Expansion is provided onPiers I, II and I\ r .
The entire superstructure, except a few small details, is of steel.
The trusses are proportioned to carry a moving load of 3000 lbs.
per lin. foot, hut in calculating the effects of a moving load, the por-tion of any strain in excess of that which would have been producedby a uniform load of equal amount was taken on a basis of 5000 lbs.per foot. The top lateral system is proportioned to resist a wind pres-sure of 300 lbs. per lin. foot and the bottom lateral system 500 lbs.per lin. foot. The strains are given on Plates 13 and 19.
The floor system was designed for an uniform load of 6000 lbs. perlin. foot.
The compression strain in the top chord is limited to 14000 lbs.per square inch of balanced section.
The tensile- strain in the bottom chord is limited to 13000 lbs.per square inch and that in the web members is somewhat lower.
The weights of iron and steel in the through spans are as follows :
Two spans,lbs.
i
Average of two spans,lbs.
Steel..
2 167 680
1 083 840
Wrought iron.
11 370
5 865
Cast iron.
42 550
21 275
Total.
2 221 600
1 110 800
The weights of iron and steel in the deck span are as follows:
Steel. 740 34G lbs.
Wrought iron. 1 936 “
Cast iron. 13 206 “
Total. 755 488 “
The specifications under which the superstructure was manufac-tured are given in Appendix F.
The dates on which the several trusses were erected are shown inthe following table:
First iron placed.
Span swung.
Deck span I- II.
June 4th, 1888.
June 8th, 1888.
East Through span 11-1II.
May 22d, 1888.
May 25th, 1888.
West Through span III— IV.
Feb. 15th, 1888.
Feb. 19th, 1888.
The timber floor, which was designed to carry a railroad track only,was put on by the company’s men, working under the direction of theResident Engineer. The painting was done in the same way.
The timber floor was subsequently altered to a highway floor underthe direction of Mr. E. P. Butts, then Resident Engineer, Burlington
Bridge, in the fall of 1890. The plans of this highway floor are givenon Plate 20.
The total cost of the superstructure is given in the following table:
Through Spans.
Iron, Steel and Ornamental Work.
$97 676.21
Freight Charges on same from Chicago .
3 048 26
$100 724.47
Erection.
20 359.66
12.98
Freight on above.
1.83
$121 098.94
Deck Span.
Iron and Steel.
33 907.60
Freight charges on same from Chicago .
994.15
34 901.75
Erection.
7 040.84
Cement, iron borings, etc.
6.50
Freight on same.
.91
Work-train service.
46.93
41 996.93
Railroad Floor.
Material.
4 403.09
Freight.
216.36
Labor.
1 621.22
Work-train service.
16.00
6 256.67
Highway Floor.
Material.
5 603.72
Freight.
134.88
Labor...
3 720.35
9 458.95
Painting.
Material.
847.68
Freight.
13.08
Labor.
3 633.32
4 494.08
Total Superstructure.
$183 305.57