April 5, 1890
The Lexington extension of the Louisville Southern Ry, crosses the Kentucky River at Tyrone, Ky., on a steel cantilever bridge, which is the longest and highest yet erected in America.
In the early part of last year the railway company contracted with the Union Bridge Co., of New York, to design and construct the super-structure, and with Hopkins & Co., for the cylinder foundations, the latter being from the plans of Mr. John Macleod, C.E, Chief Engineer of the railway company.
To the courtesy of the Union Bridge Co. we are indebted for the drawings from which our cuts are made, and to Mr. John N. Ostrom. C.E. engineer in charge of erection, for the following brief description of the work on the super-structure.
The original plan contemplated the erection of the cantilever spans first and following them with the approaches: the material was also to be hoisted from barges loaded at Frankfort, Ky., the most convenient railway terminus. But owing to some unexpected delay in completing the cylinder foundations, resulting from the controversy with the contractor, this plan was reversed, and the approaches were first built.
The material for the west approach was hauled to the track level and erected by overhanging deck-travelers, working from the abutment toward the anchor tower.
Upon the completed falsework a through traveler was set up, with the legs straddling the arm in the usual manner, but with two tracks on each side instead of one.
When the main tower was built work was commenced on the shore arm of the cantilever, commencing of course, at the tower and carrying it forward to the coupling with the anchor tower.
All material was hoisted at the main tower to the level of the traveler track, and then run back on push cars to the traveler and hoisted into place.
After the shore arm was coupled to its anchors the split-traveler was taken down and a deck overhang traveler was built for the erection of the river arm of the cantilever and half of the suspended span. All material for the river work was hoisted directly from barges, as contemplated in the first plan. While work was in progress on the west side of the river, the east approach and shore arm were commenced and carried forward in a similar manner to that already described, except that the traveler used in erecting the falsework of the shore arm of the cantilever was made strong enough to build the main towers, thereby gaining time. Another point of difference was that the material for the east viaduct was hauled up hill on an inclined railway by a hoisting engine.
The coupling at the centre of the suspended span was easily and rapidly accomplished.
Before the east half of the suspended span was commenced, the opening to be closed was accurately measured by a suspended tape, and the adjusting apparatus was so set that the bottom chord should slightly overlap, leaving an opening at the centre joint of the top chord. The apparatus was so nicely adjusted that it was only necessary to slightly raise the ends of the bottom chord bars to permit the driving of the centre pin, which work was completed in about 15 minutes for each side, without touching the adjusting machinery meanwhile.
When the centre section of the top chord was swung in place an opening of 1 ½ ins. remained: and to close this, the adjusting apparatus was released and the arm sank quickly into place. While performing this work the working traveler was on the east half of the suspended span, and the adjusting machinery on that side was not released. This adjusting machinery was one of the most important and interesting features connected with the erection of the bridge. It was designed by the Union Bridge Co., and is shown in the accompanying sketch. The wedge being fixed between rollers, well in toward its heel, raised the centre of the suspended span above the final positions.
Consequently, to make the center connection it was only necessary to slacken the adjustment nut and allow the weight of the suspended span to force up the wedges and the centre sunk into place. It was also possible to arrest the lowering of the spans at a point or instant of time. Baird Bros., who had the contract for erection under Union Bridge had rearranged the machinery to one form here should by wisely putting the frame on top of the upper chord, to obviate the necessity of an extra swinging platform for the men: but the same arrangement could not be made with the lower chord. Wedges in both frames were so arranged that scrolling up on the nuts pulled the wedges from between the rollers. Safety blocks, of wood, were placed in between the frames to prevent the possibility of the work starting before the proper time. When these blocks were removed, a very slight turn of the nuts became the quiescent friction: the wedges popped up from between the rollers, and the centre of the suspended span dropped to a bearing. The sudden drop was undesirable, and in the future apparatus of like kind it will be so arranged that the wedges must be drawn out and stopped at pleasure, thus keeping complete control of the suspended span. The comparative time occupied in erection on the east and west side is shown in the following table with dates.
The erection of the west side progressed slowly for several reasons.
In the first place, the contractors for the foundations and for the erection were on the ground at the same time, and since the erectors came late it was not possible to place the plant in the most advantageous position until foundation work had been completed and its plant removed. Besides this the top traveler for overhanging portion, was an old one used at Poughkeepsie, which was cut down considerably and which took as much time as would have been required to build a new one. Men were scarce or this work would been begun earlier, and completed before the traveler was needed. On the east side the erection was very rapid as the erectors had the whole ground, the travelers were all ready to go up rapidly, and the organization of men had been skillfully perfected.
Not a life was lost: but there was quite a number of distressing but not serious accidents.
The speed of erection was very much facilitated by the accurate fitting of the work and the precision with which centers of foundations were located, so that very little fitting and adjustment was necessary. The greatest item of time in erection was the construction of travelers and falsework for shore arms. A traveler was erected for west approach, which was taken down and erected for hoisting falsework for west shore arm, and in turn another was set up to erect main towers. Then a through traveler was constructed to erect the shore arm and a final deck traveler was used for the river arm and suspended span.
One deck traveler could have been used for shore arm and river arm by modification track-by running falswork to top of truss: but this increase in height of 60 ft, meant a large increase in the bill of timber, besides obstructing to some extent the hoisting of material, which must have been passed through the falsework to swing into position: but the plan had been tried and found less economical than to put up a through and deck traveler.
However, the problem in the future is to reduce the material in the falswork and to simplify travelers.
Under each shore arm were 250,000 ft. B.M. of timber. Four hoisting engines were used, one on the deck and one on the ground, east and west banks.
The maximum number of men employed was about 135, and the minimum number was 65.
The bridge was absolutely required by the railway company to carry a train on or before Aug. 29, in order to save the Lexington subscription.
The Union Bridge Co, promised it on Aug 25, and delivered it practically finished for the first train on the 24th, the time of construction and erection being about six months.
Including foundation, the total from breaking ground to completion was about seven months.
It should have been started earlier, that while the eye-bars were made at the Athens shops of the Union Bridge Co., the remainder of the shop work was sublet to the Detroit Bridge & Iron Works, and a proportionate share of credit for accurate workmanship is due to this company.
This item was found in the Engineering News Report of April 5, 1890, in the University of Kentucky Library Microfilm collection. It was transcribed and provided courtesy of Jodie Wells, president of the Tyrone Bridge and Rail Co.
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