This bridge has a fascinating history which was extensively detailed in period literature. The story begins with the construction of a railroad bridge in 1892 at this location. The 1892 bridge was built by the Edge Moor Bridge Company of Wilmington, Delaware. It consisted of pin-connected through truss spans over the river, and an extremely long series of trestle-style approach spans at the southern end. The truss spans were built on stone piers. The design of this bridge, particularly the truss spans was unusual. It was built as a single-track bridge, however the width of the trusses was very wide (34 feet). The idea was that in the future, the truss spans could be converted into a double track bridge by adding a third truss line in the middle to support the additional loads.
However, moving into the 20th Century, when the need for a double-track bridge arose, it was instead decided that it would be better to replace the bridge because the loading needs for trains at this time was much higher than anticipated in 1892. However, it was determined that the original stone piers could be adapted and reused to support a new bridge.
Railroads have traditionally placed an unparalleled priority on maintaining flow of railroad traffic during any bridge project, even complete bridge replacement on the same alignment. This historically led to amazing and creative engineering efforts, and this bridge is no exception. In general, the method for replacing this bridge was similar to that used for the replacement of other single track truss bridges with double track bridges. The new bridge, being wider than the old bridge, would be built around the old bridge, then the old bridge would be removed. However, the Kenova Bridge presented a larger challenge than usual because the old bridge was unusually wide as noted above.
Detailed discussions of the project are described in the historical literature linked to at the top of this narrative. Please read those for a detailed, step-by-step description of the construction sequence. A few specific and more interesting/unique aspects of the construction are noted here.
The new bridge trusses were wider than the original trusses, and as a result, reusing the piers meant making some changes to the piers, which as-built were a little too narrow for the replacement bridge. A unique riveted steel "pier girder" was designed to address this problem. These giant riveted girders were partially assembled in the shop, and the largest girders weighed 127 tons and were so heavy they caused visible deflection (sag) in the special railroad cars used to haul them. A historical photo to the right shows this. These pier girders were the width needed to support the new trusses. They included two special pedestals set in a ways from the ends of the girder. These pedestals are the points in which the pier girder bears on the stone piers. Looking at the bridge today, you can see the giant pins where the pedestals are connected to the girders. This can also be seen in the historical photo to the right.
Portions of the truss spans were erected using the cantilever method, which avoided having to place falsework in the river. Temporary bracing that anchored a span under construction to adjacent spans enabled this form of construction. The erection of the 520 foot main span was accomplished using the cantilever method. The span was constructed by erecting the trusses from each end, meeting in the middle where the two halves were joined. This erection method appears to explain why this span, which is otherwise completely composed of riveted connections, has eyebars and pin-connections for the four center panels of the bottom chord. The pin connections allowed for the bottom chord to be movable to a certain extent during erection. The rather complicated process of connecting the two halves took advantage of this ability, with the bottom chord being allowed to sag somewhat until the halves were connected, at which time the bottom chord was moved into its normal position. The historical photo to the left shows the bottom chord with a visible sag before the two halves were connected (called "closing the span" by engineers of the period).
The design of the bridge appears to have been handled exclusively by the railroad (Charles S. Churchill as chief engineer) and the American Bridge Company (C. W. Bryan as chief engineer); it does not appear that any consulting engineers were a part of the bridge project.
The main span of the bridge is from center to center of bearings 520 feet, 10 7/8 inches. The clear span is 518 feet. Center to center of truss lines, the current bridge is 43 feet wide. The actual width of the railroad deck is estimated at about 24 feet.
At some point in its more recent history, the deck plate girders on the approach spans of this bridge were replaced with welded girders.
The above photo shows the earlier stages of the bridge construction, and also offers a good portal view of the previous truss bridge.
The above photos show parts of the bridge being shipped to the site, and help give a sense of how massive the bridge is. The photo to the left shows an end post, and the photo to the right shows a floor beam.
The above photos show the construction of the bridge around the existing truss bridge, allowing trains to continue to use the bridge during construction.
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