Modernization of the Cairo Ohio River Bridge
As profiled earlier in the year, the Cairo, Illinois Ohio River Bridge that carried the Illinois Central Railroad, a route that is now used by the Canadian National Railway. It was the first railroad link completed between Chicago and New Orleans, and revolutionized rail travel along the Mississippi River. The 52 truss steel span bridge had a length of 10,560 feet, the longest of any metal bridge in the world. The total length, including trestles, was 20,461 feet, or 3.875 miles.
The need for a replacement came as early as 1921, when plans were submitted to the War Department for the replacement of the Whipple trusses with a double track superstructure, reusing the existing piers. But opposition led to that idea dying fairly quickly. In 1932, a supplementary freight line for the IC was completed from Edgewood south to Reevesville, connecting to an existing IC line from St. Louis that utilized the existing Metropolis, Illinois-Paducah, Kentucky Bridge. The secondary line connected to the IC at Fulton, Kentucky.
On May 25, 1946, the IC requested Modjeski and Masters to complete a study of the current condition of the Cairo Bridge. In the report, the company stated that the reinforcements to the bridge in 1914 and in the 1930s increased the dead load carried by the spans and that there were a number of points on all of the spans were the pins had been worn out. As a result, the distribution of stresses were hammered along the bars of the end hanger members - where one bar, for instance, carried 97% of the total live load stress due to pin wear of an outer eyebar.
The expansion rollers had also been worn to an elliptical shape, and the shoes had developed pockets into which the rollers fitted that resisted expansion movements. As a result, some cracks were formed in the stone masonry of the piers that required steel banding. The report also stated that the Whipple trusses under live loads were overstressing the bottom chords by 30% and 45% of the 518.6-foot and 400-foot spans, and that there were varying amounts of overstresses in the top chords and end posts, and bottom laterals under high wind.
The report recommended that the live loads and speeds not increase on the Cairo Bridge, and that the existing crossing be replaced as it had reached the end of its useful life. To keep the bridge in service, an anemometer was installed so that when high winds were reported, trains would be prohibited from the bridge.
Plans to replace the bridge began in July 1947 under Modjeski and Masters. Early studies focused on constructing a bridge 150-feet upstream from the existing bridge and using some of the existing approaches, given that there were concerns with high water and drift hazards that a temporary bridge could encounter during the reconstruction process. During the development process, consideration was given to a channel span of 648-feet, the same as the Louisville & Nashville (L&N) Bridge at Henderson, Kentucky, but to give a good arrangement of trusses on the new bridge, the channel span length was increased to 688-feet, with a navigation clearance of 668-feet, or 20-feet more than the L&N Bridge.
After discussing the options with the Army Corps of Engineers, a revised plan was developed for a new bridge 150-feet upstream, with the main channel closer to the Illinois shore, with a main cantilever span for the channel with a 721-foot length. Piers IX through V would remain in place, with new piers C through G being replaced. On the Kentucky approach, 255-foot deck spans would be constructed to replace three existing 405-foot through spans. A formal report was submitted to the War Department in July 1947 for approval.
A public hearing was held on August 26, and opposition developed among river boat interests who called for a longer clear navigation. The IC Metropolis Bridge was 700-foot, and the Cairo Highway Bridge was 800-foot. The desired length was 800-feet. Instead, the IC submitted an application for reconstruction of the existing bridge on the existing alignment, which was approved by the Chief of Engineers and the Assistant Secretary of the Army on July 6, 1948.
Because of the poor conditions of some piers, a concrete jacket would be needed around Piers X, VIII and VI to stabilize them for the long term. An encasement, two feet thick, was designed to be attached with expansion anchors to alternate stone courses by a pattern of anchors.
In early 1948, Modjeski and Masters were requested by the IC to prepare plans and specifications for the reconstruction of the Cairo Bridge. The new design incorporated all riveted through truss spans of the same lengths as the original bridges, except for the 1,215-foot section over the Kentucky bank where three 405-foot through trusses would be replaced with six 200-foot deck trusses. Specifically, the superstructure consisted of two 518.11-foot and four 400.11-foot Warren Through truss spans, and six 197.7-foot deck truss spans. The widths would vary, 25-feet for the 518-foot spans, and 22-feet for the 400-foot spans. The new construction involved 3,884.675-feet.
The contractor submitting a bid was required to do the work of constructing the new spans and shifting the spans in a manner as to meet the navigation requirements set forth by the Department of the Army. Because of the high cost of detouring all freight to the Metropolis Bridge, the bidding contractors were required to state as an item of their bid the number of hours of detour time which was evaluated at one-half the estimated cost of detouring trains. An equal penalty was provided for exceeding the time in the bid.
The scope of the work involved in Substructure Contract No. 1 was to complete changes and additions to the substructure of the existing bridge to adapt it to the new superstructure. This involved the encasement of Piers VI, VIII and X with reinforced concrete anchored to the existing stone and supported on tremie seal supplemental footings, which were to be supported by steel bearing piles. It also involved cutting recesses in Piers II to V for the bearings of the new deck truss spans, and the construction of three new reinforced concrete piers at the midpoints of each of the through spans between Piers II and V for the new deck trusses. Bids for this contract were received on May 4, 1949 and on May 21, the contract was awarded to the Kansas City Bridge Company and the Massman Construction Company, who had bid jointly. The contractor began shipping in equipment in early June and construction began on July 19. The contract required that the work be completed for the superstructure construction within one year and that all work on the pier be finished 150 days after that.
The first concrete pour for this contract was made at Pier C on November 2. The initial process involved batching the three mixer trucks at a ready-mix plant that was located about 1/4-mile north of the north end of the bridge, then hauling the trucks to the top of the levee, back down the trestle where the concrete would be dumped into a hopper, and from the hopper into 1.0 cubic yard buckets on a pontoon which would be transported across the river via a tugboat. The concrete would then be transferred via a pumpcrete machine by crane to the vicinity of Pier C. This was a very slow process, and only 10.5 cubic yards of concrete were poured per hour.
To speed things up, a narrow, 3-foot gauge railroad was built from the Kentucky bank to Pier C and employed one engine and two flat cars in the spring of 1950. A 6.0 cubic yard hopper was set up over the river end of the railroad so that the concrete could be dumped by gravy into the three 1.0 cubic yard buckets that were discharged into the forms by a crawler crane. The pours were faster, at 25 to 30 cubic yards per hour.
The scope of the work for Superstructure Contract No. 2 was to replace nine through trusses, six Warren through trusses and six deck trusses. The contract specified that the bridge would continue to operate through the reconstruction of the superstructure, with a bonus and penalty of $200 per hour for time either saved or lost compared with a total number of hours of anticipated detour time that each contractor would provide. Bids for the superstructure were received on September 1, 1949 with the American Bridge Company being awarded the contract with a detour time of 292 hours listed in their proposal.
The contract specified that the American Bridge Company was limited to the erection of the spans on falsework adjacent to their final position, which would then be rolled into place. To facilitate quicker construction, two of the 200-foot deck truss spans for the Kentucky bank were adapted to provide falsework for the river spans. The trusses were slightly strengthened and a few members were added to extend the spans for full-length falsework. Two short spans were supported at each pier by a steel bent resting partly on the pier and partly on a steel pile foundation, and at midpoint by a common steel bent supported by a steel pile foundation. They could then be moved by picking up the components and moving them via a barge.
The contractor began assembling crews and equipment on April 24, 1950, and preliminary work involved the construction of a field office and the preparation of barges for derricks and for mounting structural towers for moving falsework spans. Falsework bents were built for Span 10, and two falsework deck spans were completed. Preparations for erection work were finished on September 2.
Due to the complexities of the requirements as to the maintenance of river and rail traffic, the contractors developed a scheme of erecting the new truss and the disposal of the old span, which involved the rection of a span on falsework complete with track, the rolling out the old span onto falsework, the rolling in the new span, and the launching and salvaging of the old span. The old spans were rolled out and set down on temporary end supporting framework (sled) on the upstream side of the bridge, and were launched into the Ohio River. It was a method that was far cheaper than dismantling the span component by component.
The 200-foot deck spans on the Kentucky bank were erected near their final position and were rolled in. The falsework consisted of steel bents that were kept to a minimum by trussing up the bottom chords with wire ropes in four-panel lengths for the initial stage, and then after the web members and top chords were filled in, by cantilevering the remaining four panels. The two 200-foot deck spans replaced one 400-foot through span, and were rolled together into place.
Contract No. 2 work was completed in May 1952 with only 119 hours and 45 minutes of detour time, much shorter than the 292 that the company had requested. The shortened time was attributed to the launching of the trusses.