THE CAIRO BRIDGE.
13
IY_ SEVEN 400 FT. THROUGH SPANS. y.
SUPERSTRIT CTURE.
The superstructure of the bridge proper consists of nine throughspans and three deck spans. The two through spans over the channelof the river are each 518 feet G inches long between centers of end pins,divided into 17 panels of 30 feet 6 inches each, the trusses being G1 feetdeep and placed 25 feet between centers. The other seven throughspans are each 400 feet long between centers of end pins, divided into15 panels of 26 feet 8 inches each, the trusses being 50 feet deep andplaced 22 feet between centers. The three deck spans are each 249 feetlong between centers of end pins, divided into nine panels of 27 feet 8inches each, the trusses being 30 feet deep and placed 18 feet betweencenters. Expansion is provided on piers I, III, V, VII, IX, XI and XII.
The entire superstructure, except the pedestals, is of steel.
The trusses are proportioned to carry a moving load of 3000 lbs.per lineal foot, but 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 lineal foot, and the bottom lateral system 500 lbs.per lineal foot. The strains are given on Plates 12 and 20.
The floor system was designed for a uniform load of 6000 lbs. perlineal foot.
The compressive strain in the top chord is limited to 14000 lbs. persquare inch of balanced section.
The tensile strain in the bottom chord is limited to 13000 lbs. persquare inch, and that in the web members is kept somewhat lower.
The weight of iron and steel in the various spans is as follows:
TWO 518 FT. 0 IN. THROUGH SPANS.
Material.
Weight of two Spans.
Average.
Steel..
4 048 674 lbs.
2 024 337 lbs.
Wrought Iron .
6 255 “
3 127 “
Cast Iron..
74 540 “
37 270 “
Total_
4 129 469 lbs.
2 064 734 lbs.
Material.
Weight of seven Spans.
Average.
Steel...
7 720 275 lbs.
1 102 896 lbs.
Wrought Iron.
28 278 “
4 040 “
Cast Iron.
192 994 “
27 571 “
Total.
7 941 547 lbs.
1 134 567 lbs.
THREE 249 FT. DECK SPANS
Material.
Weight of three Spans.
Average.
Steel...-
1 377 316 lbs.
459 105 lbs.
Wrought Iron.
7 834 “
2 011 “
Cast Iron.
22 615 “
7 538 “
Total.....-
1 407 765 lbs.
469 254 lbs.
The weight of the twelve main spans is 13 478 781 pounds.
The specifications under which the superstructure was manufacturedare given in Appendix G.
The dates on which the several trusses were erected are shown inthe following table :
Piers.
Begun.
Swung.
Ill.....
December 21, 1888.
December 24, 1888.
11-111...
March 16, 1889.
March 21, 1889.
III-IV__
May 6, 1889.
May 8, 1889.
IV-V ...
June 3, 1889.
June 4, 1889.
V-VI.....
June 27, 1889.
June 30, 1889.
VI-VII..
July 26, 1889.
July 28, 1889.
VII-VIII...-
August 26, 1889.
August 28, 1889.
VIII-IX.
August 21, 1889.
August 23, 1889.
IX-X....
October 30, 1888.
November 5, 1888.
X-XI... ..
September 29, 1888
October 10, 1888.
XI-XII...-.
July 26, 1888.
July 30, 1888.
XII XIII ____
August 3, 1888.
August 15, 1888.
The timber floor was put on by the Company’s own men, workingunder the direction of the Resident Engineer. The delay in getting tim-ber for this work retarded the completion of the bridge for some time.The painting was done in the same manner.
APPROACHES.
The East or Kentucky Approach consists of 3256 lineal feet of steelviaduct and 4594 lineal feet of trestle, 1080 feet of which is composedof frame bents and the balance of pile trestle. The end of the trestleis practically at the foot of the grade.
The construction of the viaduct was begun on November 23, 1888,by the excavation for the foundations. Pile driving was commenced onthe next day. The concreting about the piles was commenced on the17th of January, 1889.
The placing of cylinders for the piers was commenced on February19, and all were erected by April 6. The piers were all concreted bythe 1st of May.
The concrete placed on the outside of the cylinders during freezingweather was found to be defective, and all of this defective material wasremoved and replaced by sound concrete in June, 1889.
The concrete used in the cylinder piers was composed of Louisvillecement, sand and crushed stone, in the ratio of one, two, and three andone-lialf. In the upper two feet of the cylinder, Portland cement wassubstituted for Louisville, and a steel cap was subsequently put on topas a covering.
The amount of material in the substructure of the Kentuckyapproach is given in the following table :
Piers.
Piles,lineal feet.
Concrete,cubic yards.
Steel,
pounds.
Timber,feet, B. M.
21 Cylinder Piers...
16 964
540
2 894.5
863 812
323
Timber Pier.
13 359
Total...
17 504
2 894.5
864 135
13 359
The erection of the superstructure was begun on the 25tli of April,and completed on the 19th of September.