Technical Description Of Old Camp Nelson Bridge Replacement

By W. H. Fisher - 1928

The new Camp Nelson Bridge, just completed on Lancaster Road, eight miles south of Nicholasville, across the Kentucky River, has a location at once scenic and of historic interest.

The name Camp Nelson was first applied during the Civil War to a Union military encampment and system of fortifications established on the hills just northeast of the bridge site.

The new bridge also replaces a picturesque and extremely interesting old wooden bridge, which, erected in 1838 and still standing, though condemned for use, is a unique monument to the past and to the men who built it; unique in that it is probably the oldest wooden span still standing in the United States, and also in its length of span and type of construction. It was built for the state of Kentucky by Lewis V. Wernwag, a native of Pennsylvania and eminent bridge builder of his time. Its construction is said to have cost $30,000, including the masonry abutments.

In its type of construction, the old wooden bridge consists essentially of three timber arches, each arch rib stiffened by timber trusses extending the full length of the bridge. Each arch rib is made up of six timbers sized six inches by 12 inches, arranged two horizontal and three vertical. As each arch rib passed through stiffener trusses, the posts and diagonals of the latter are neatly dipped to allow the arch rib to pass through intact, all butt-joints of the arch rib members being located at and concealed by the truss posts. The exceptional workmanship, shown in joint fittings throughout the bridge, is nothing short of marvelous and is tangible evidence of the extreme care taken in its construction.

A 235-Foot Span

The three arch ribs have a clear span of 235 feet, setting on solid masonry abutments at each end, and are held in vertical position by a timber top lateral truss system extending full width of the bridge, attached to the tops of the three stiffening trusses, which separate the two separate roadways provided, each 12 feet in width.

The bottom lateral system consisted of one inch square wrought iron tire-rods, arranged diagonally, crosswise beneath the stiffener trusses. Many of these are now broken off due to excessive settlement of bridge.

The entire bridge is roofed and sided over as weather protection. For the reader who may be interested, a more detailed description of the construction details of this old wood bridge is to be found in Engineering News Record, issue of February 9, 1928.

Built at a time when exact methods of bridge stress analysis were unknown, we can only pause in wonder and admiration at this old bridge, which would be a credit to a modern designer in its type, and which with its 88 years of continuous service presents a record unparalleled in American bridge annals. Interesting, indeed, would be a chronology of the nation's historical events which this old bridge has outlived, extending back to the days when Kentucky was still in the pioneer stage of its development, when vast unsettled domains lay west of the Mississippi, and Andrew Jackson was president. Could it but speak, it could tell us of General Scott and the Mexican War, of those anxious days leading up to our Civil War, and of the latter momentous conflict itself, which several times threatened a tragic ending to the bridge.

Narrow Escapes From Fire

It was stacked for burning, by both the Union and the Confederate forces, but each time local townsmen succeeded in dissuading them from their purpose. With the opposing forces camped on either side of the river, it seems a miracle that the bridge passed through the war unscathed, when nearly every other bridge along the river was then destroyed.

But the stoutest works of man are, like himself, but mortal, and must eventually yield to the ravages of time and weather. With the old bridge, too, the increased demands of modern traffic were undoubtedly an accelerating influence toward the ending of its period of usefulness.

Gradual settlement of one of the arch ribs had been observed for some 15 years back, induced probably by a combination of causes, and the floor became noticeably too weak for modern loads.

A new floor system was installed during the summer of 1925, which gave temporary relief, but by the following fall, the continued deformation of the arch ribs had reached a point considered dangerous, and the bridge was closed toward the last of November 1925, by the Highway Department, first to heavy traffic only and shortly afterward to all traffic.

A ferry was installed in December, following, just above the bridge, operated by local parties which has taken care of traffic until completion of the new bridge. Several moves were made during the next few months to secure the repair and reopening of the old bridge; but after thorough investigation, it was decided that the large cost involved in attempting the necessary repairs, with no assurance forthcoming that such repairs would prove permanent, would not be justified from an economic standpoint.

Impractical Sentiment

In passing, it should be observed that while everyone appreciates the historical significance of the old bridge, and while the strong sentiment evidence looking toward its preservation as a monument to the past is a worthy one, nevertheless, in the present day, everything, even sentiment, must sometimes be measured in terms of dollars and cents; especially where the expenditure of public funds is involved, and the ever-recurring question arises: will the ultimate returns on the investment be satisfactory to the taxpayers, spent along the lines for which they were intended? The annual cost of maintenance is, also, of course, a vital factor in arriving at conclusions in such matters.

With the closing of the old bridge, the highway department engaged in making comparative studies and investigations, as a result of which a new bridge was unanimously decided upon. The site selected, downstream or west from the old bridge some 100 feet average distance, also had the merit of eliminating several very sharp curves in the old road alignment.

Work on plans for the new bridge was started early in 1926, and completed by June 1st of that year. The securing of the necessary right of way by Jessamine and Garrard counties was also initiated in the spring of 1926.

Contracts for the new bridge were sent June 22, 1926, in two parts: one covering the fabrication, erection, and painting of the 275-foot steel span across the main river channel; the other including all substructure and concrete work. The contract for the steel span was awarded to the Mt. Vernon (Ohio) Bridge Company for $42,821.82, who completed same; but owing to unforeseen difficulties in securing some of the necessary right of way, which was not finally obtained until the following winter, it became necessary to re-advertise the substructure and concrete work.

On February 22, 1927, the new contract was awarded to A. M. Cook and Company, of Wartsburg, Tennessee, for $66, 725.70. A subsequent contract for the fill approach to the south end of the bridge was awarded September 28, 1927, to Moynahan and Turner, of Mt. Vernon, Kentucky, for $8,040.

The New Bridge Plans

The plans for the new bridge called for a total length of 543 feet, including the 275-foot steel span, with a clearance of 60 feet above extreme low water of the river, the steel span carrying a seven-inch reinforced concrete road-slab and curbs. Abutment Six at the south bridge end and Pier Five are both founded on creosoted pile footings, all other piers and Abutment O being founded on solid rock.

The deepest footing is at Pier Four, which extends 21 feet below low-water level of the river, although Pier Three on the south river edge is practically the same depth. Pier Four is also the highest pier, the total height above the footing being 76.4 feet. All piers and abutments are reinforced throughout, except column footings, some of which are without steel. Piers Two and Three, which support the steel span, have circular columns of four feet, eight inches top diameter and side batter of seven-sixteenths inch per foot; connected with 15-inch web-wall.

The concrete approach spans to steel span are deck-girders each 53 feet long; two being used at the north end, where the alignment is straight, and three used at the south end, where the alignment is a 25-degree curve with transverse super-elevation on the roadway surface. A new constructive feature was introduced in these deck-girders, namely that the three beam stems of each girder were cast first, followed by a later pour of slab and curbs, the two runs bonded together by use of concrete keys eight inches by ten inches and two-inch thick. These keys were spaced at 18 inches centers along the top of each beam stem at the base of the slab. This method greatly simplifies construction as compared with the old method of pouring beams and slab monolithic, as the slab steel does not have to be in place at the time beams are cast.

All piers and abutments, deck-girder spans to base of handrail, and road slab across steel span are of Class A or 1:2:4 mix concrete. The roadway width is 20 feet, except on the three south approach spans, where standard curve widening obtains. Roadway wearing surface is to be Kentucky rock asphalt, two inches thick, which will not be placed, however, until warm weather allows its successful application.

The handrail on concrete spans is of the rectangular spindle and baluster type with posts at the ends, quarter and center points of each span, all of Class D or 1:2:3 mix concrete, reinforced. The base rail between the posts was cast first, followed by posts and balusters being cast monolithic over length of span. Four-inch by six-inch pockets were left in the base rail, into which spindles were set before casting of balusters, spindle bases being grouted in afterwards.

Expansion joints of one-inch bituminous felt are provided where two concrete spans meet, the felt extending through the handrail; splitting one post, half of which is on each span. Bronze plates, three-fourth-inch thick, are provided under expansion ends of deck-girder beams over piers which allow a free sliding movement. Steel expansion angles are installed at junction of steel-span with concrete spans on either end.

Plans for the 275-foot steel span include two full-riveted trusses of the "Pennsylvania" type, spaced 23 feet apart, with 11 panels of 25 feet each and a maximum height of 40 feet. Cast steel pedestals are being used at the end bearings, the north or Pier Two end being fixed; while at the south or Pier Three, a nest of five, eight-inch diameter rollers allow expansion.

The floor system consists of transverse 30-inch, 129-pound I-beams at each panel point; longitudinally connected with five sets of 20-inch, 62-pound I-beam stringers at four feet, six inch centers across the bridge. The seven-inch concrete road-slab rests directly on this system.

The total weight of structural steel used is 601,205 pounds, which includes some 15,000 rivets used; and also 16 cast iron drain pipes, which are installed through road-slab. Handrail on steel span consists of two steel six-inch, Z-section lattices, attached to truss posts.