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Removal of Old and Erection of New Bridge

"The new north abutment wall was located 40 feet back of the old one. In preparing the foundation for the same it was necessary to remove the anchorage of the old cables, and to construct temporarily two anchor chains attached to the second pair of old towers. Previous to this wrought-iron anchors had been imbedded into the foundation of new pier No. 1, which had been built up to obtain the requisite weight for the temporary anchorage.

"These anchor chains were composed of steel eye-bars, which were on hand from the intended suspension bridge. Each chain was made adjustable in length by means of a transverse screw rod, and four sets of eye-bars, forming a funicular machine. The chain could thereby be shortened with comparatively little power. To the cable the chain bars were attached by means of two wrought-iron plates. Between these plates were cast-iron friction clutches holding the cable, and pressed and held together with bolts passing through the plates. These were attached to the cable as near to the towers as possible. To prevent slipping of the clutches on the cable, the wire wrapping was removed, and spikes driven through the cable wires behind the clutches.

"The transfer of the anchorage was done without mishap while travel as usual was going over the old bridge on both tracks. The pull per anchor chain was at times 160 tons.

"Under the first north span of the old bridge, false works had been built, which, after the transfer of the anchorage, supported the old roadway, and at the same time served for the erection of the iron girders for the new bridge. No other part of the old bridge was removed till after the erection of the new channel spans.

"In the false works for the latter an opening 100 feet wide near the Pittsburgh and was left for navigation, and temporarily bridged over with wooden Howe trusses. The false works were further so arranged as to clear one track on the old bridge, on which the team-travel moved in squads in alternate directions.

"To prevent accidents from anything falling from above on pedestrians or teams below, the false works were covered with a platform of planks, which were afterwards used for the new floor. The upper staging was built up on the outside of, and to half the height of, the trusses to be erected; at that height a traveling derrick, 30 feet high, moved on a track of iron rails. All material for the channel spans was lifted (by a hoisting engine near the south Pittsburgh end) to the platform, on which a temporary track wa laid, and all material transferred on push-cars.

"With another hoisting engine, conveniently located on the up-stream end of pier No. 3, the material for both spans could be handled and put in place without moving the engines.

"The Pittsburgh span was erected first. After the pier posts were put into position, the bottom chords and connecting web-members were put in place. The top chord sections, weighing from 7 to 9 tons, were picked up and placed on the verticals, one after the other, from each end in each truss. For closing the top chord, the two middle chord-sections were raised at one end till they met, and then sprung into line by pulling down these ends towards the bottom chord with block and tackle acting as a funicular machine.

"The false works of the Pittsburgh spans had settled more than was anticipated. Before it was possible to close the top chords the different panel points had to be jacked up 2 to 6 inches. No such trouble was experienced with the other span.

"During the erection of the channel spans no little anxiety existed at the possibility of an accident from some heavy weight dropping to the platform and breaking through to the constantly crowded old bridge below. Fortunately, the work was completed without such accident, but there were two casualties, which both resulted luckily. One man fell from a height of 80 feet into the river, but was picked up and next morning was at work. Another man fell from a height of 50 feet into shallow water; he was able to report for work after two days.

"The iron floor construction was suspended to the trusses after these were swung.

"The detail of connections in the Pauli trusses being simple, the erection of the steel and iron work went off smoothly, and with no more expense than in parallel chord trusses. It commenced in the middle of September, 1882, and was completed December 31st, 1882.

"To the new iron floor construction the old bridge floor was temporarily suspended with iron plate-girders at the south end of the bridge. These down-stream towers were removed first, together with the cable they supported. The old bridge floor where it was not suspended from the new bridge was held up on wooden trestles.

"Three plate-girders in each span, supporting the down-stream track and sidewalk, equal to half the width of the new bridge, were put into position, and the paving for one car-track finished for the entire length of the bridge, without interrupting travel on the old bridge below.

"Temporary wooden trestle approaches, with plank floors for one track, were built at both abutments, because the filling in would have interfered with travel on the old bridge. All this work was much retarded by a stormy and severe winter. Travel was turned over the new bridge on the down-stream track on March 19th, 1883. (33)

"During a high water, February 22, 1883, a heavy mass of ice came down the river on a swift current, and tore away a part of the false works supporting the old bridge in a place where it was not suspended from the new one. The old bridge was then in danger of falling into the river; but by promptly suspending the old floor to the new one, first with ropes and chains, and then with iron rods, the old bridge, after one and a half day's interruption, was again safe. This was the only interruption of travel throughout the whole work.

"After travel was turned on the new bridge, the gaps and openings in the abutments and piers were walled in, as stated before. The remaining old towers, cables and bridge floor were removed, and the up-stream half of the plate-girder approaches completed.

"This was done by placing in position the remaining three plate-girders in each span, and the iron columns (supporting the girders near the abutments). At the same time the erection of the hand-railing and of the ornamental cast-iron tower progressed. The adjustment nuts of the diagonal ties in the channel spans were covered with ornamental castings, which prevent tampering with the sleeve-nuts.

"The filling in and regrading of the approaches at both ends, and the building of the toll-houses and bridge office, were completed simultaneously with the superstructure.

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