To view the figures and tables associated with this article, please refer to the flipbook above.
The Eads Bridge (see article in the April 2024 issue of STRUCTURE) opened in 1874 and went into bankruptcy in 1875 when it was purchased by the Terminal Railroad Association (TRRA). As it was the only crossing of the river in the St. Louis area, they controlled the rates they charged the various railroads to cross their bridge. Local merchants, with the hope of decreasing their shipping costs, formed the Merchants Exchange Company in 1886 to build their own bridge with the company being incorporated on May 11, 1886, by the State of Illinois, “for the purpose of constructing a bridge and approaches thereto, over the Mississippi River to the city of St. Louis, Mo., from & suitable point between the north line of St. Clair County, in Illinois, and a point opposite the mouth of the Missouri River in Missouri.” The site is where the competitor bridge to the Eads Bridge was proposed in 1867 by Lucius Boomer and his associates.
Authority for construction of the bridge was granted by an act of Congress, approved February 3, 1887, Chapter 91, “An Act authorizing the construction of a bridge over the Mississippi River at St. Louis.” Section 3 of the act stated,
SEC. 3. That if the bridge shall be made with unbroken and continuous spans, it shall have at least two channel spans of not less than five hundred feet clear width each, and one span of three hundred feet clear width of channel way: Provided, That said bridge may have two spans of not less than seven hundred and fifty feet each clear width of channel-way, if thought best, instead of three spans as aforesaid, the said channel-ways to be measured at right angles to the current at any and all stages of water; and said span or spans shall not be of less elevation in any case than fifty feet above high-water mark, as understood at the point of location, to the bottom chords of the bridge, and the piers of said bridge shall be parallel with the current of the river, and there shall not be less than fifty feet at high-water mark from the surface of the water to the bottom chords of said bridge.
SEC. 11. Stated in part,
That whereas a principal reason for giving authority to build the bridge herein contemplated is to secure reasonable rates and tolls for corporations and individuals for passing over the same, the Saint Louis Merchants' Bridge Company, or its successors or assigns, shall not agree or consent to the consolidation of this bridge with any other bridge across the Mississippi River, or to the pooling of the earnings of this bridge company with the earnings of any other bridge company on said river.
The Merchant Exchange company chose George Morison as consulting engineer and Elmer Corthell as chief engineer. Morison had built several bridges using Whipple double intersection trusses, gradually changing from wrought iron to steel. They chose a site 2 ½ miles north of the Eads Bridge with lowlands on both sides of the river requiring long trestles and three long span trusses over the shipping channel. The river itself was about 1,600 feet wide at the site. The required horizontal clearance set by the enabling Act of Congress was 500 feet with a vertical clearance of 50 feet above high water. They designed their three main spans with a length of 517 feet, 8 inches and a clearance over high water of 52 feet.
They submitted their report on November 2, 1887, with three main double track spans over the shipping channel. The plans for the bridge were approved by the Secretary of War on November 15, 1888.
The spans were described as follows, “At either end of the main bridge there is about 425 feet of deck spans, [three spans with clearances of 125 feet] and on the east side there is trestle which is eventually be filled in with earth as shown on the plan, over the Alton Bee line and Wabash railways there is 175-foot double track spam and one, 40-foot girder span. On the West End of the bridge, beyond a 425 feet of deck approach, there will be an iron viaduct over ferry street about 400 feet long then 600 feet of wooden trestle, then 196 feet deck span with 40-foot girders at each end, over ferry street again and then a trestle until the embankment has reached at a height of 25 feet.
Even though Morison had built 518-feet long Whipple double intersection trusses at Cairo, Illinois, over the Ohio River, they were considered to be the longest that could be built with that truss style. At the Merchants Exchange Bridge, he decided to go with double intersection steel Pennsylvania Trusses with curved upper chords. The three main spans are built with 18 panels, each 29 feet, 6 inches. The trusses were 75 feet high in the center and are set 30 feet apart on centers, making room for two tracks placed 12 feet apart, center to center. A system of diagonal and lateral bracing is carried down the posts so as to leave a clearance of 21 feet over the railroad track, thus bracing the center part of each span for the upper 50 feet of its length. The trestles were built of piles driven 20 to 25 feet into the ground and standing 25 to 45 feet above the ground, all the members of the structure above ground being firmly braced and tied together.
The Union Bridge Company, under Charles Macdonald, built the main spans and the 425-feet flanking deck span trusses as well as the viaduct and bridge over Ferry Street and the bridges over the railways on the east and Angelica St. on the West approach. Anderson & Barr placed the foundations and masonry work. The trestle and earthwork were shared by several local contractors.
Construction started in February 1889, and the bridge opened to a grand celebration in May 1890. Tolls were not as much as anticipated, and during the financial panic of 1893, the company went bankrupt. Its competitor, the Terminal Railroad Association, took over the company and once again had a monopoly on transit across the river in St. Louis.
The approaches were rebuilt in 2005 and the main trusses in 2022 on the existing, with some modifications, piers. ■
About the Author
Dr. Frank Griggs, Dist.M. ASCE, specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer (fgriggsjr@verizon.net).