Merchants Bridge

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As St. Louis grew as a prominent railroad center in the Midwest, all traffic crossing the Mississippi River between Illinois and St. Louis utilized the Eads Bridge, completed in 1874. The Eads Bridge was funded by the St. Louis Merchants Exchange, a group of businessmen which operated industries throughout St. Louis. The Terminal Railroad Association of St. Louis (TRRA) gained control of the bridge in 1877, setting the rates for railroad traffic crossing the bridge. The TRRA was controlled by railroad tycoon Jay Gould, which also owned other railroad systems throughout the Midwest, such as the Missouri Pacific system. As part of the formation of the TRRA, several independent railroads agreed to pool resources to construct terminal facilities and tracks throughout the St. Louis area. To avoid costly tariffs, traffic being shipped east from St. Louis utilized car ferries to cross the Mississippi River.

The desire for a second bridge across the Mississippi River became strong during the late 1870s and 1880s. In addition to steep tariffs charged to cross the bridge, the bridge was poorly planned for railroad operations, with poor connections to railroad facilities on the St. Louis side of the bridge. The St. Louis Merchants Exchange again planned to construct a bridge, this structure connecting St. Louis to Venice, Illinois upstream of the Eads Bridge. A company, known as the St. Louis Merchants Bridge and Terminal Company was formed to construct a bridge and connections. A charter in 1886 granted permission to construct a new bridge across the Mississippi River on the north side of St. Louis. In 1887, planning for a new bridge began. George S. Morison was retained to design the new structure. Morison had become an esteemed bridge engineer, designing several large bridges across the Mississippi and Missouri Rivers in the 1880s. Virtually all of his long spans until this point had been Whipple through trusses. The requirements for bridges across the Mississippi River included the use of 500-foot spans, with a height of at least 50 feet. A plan was submitted to the War Department for a new bridge, and was approved in December 1888. The bridge would consist of three 520-foot steel spans, approached by three 125-foot deck trusses on either side. Several thousand feet of wooden pile trestle would approach the bridge on either side, with various steel spans over railroads and streets. The steel spans would be constructed for double track, with the timber spans constructed for a single track.

Work on the stone piers was contracted to Anderson & Barr; and fabrication of the superstructure was let to Union Bridge Company. Work began on the bridge in February 1889, starting with the construction of the stone piers. The four river piers would be constructed of pneumatic caissons and limestone quarried at Bedford, Indiana. After completion of the piers, construction began on the truss spans. The truss spans would consist of 520-foot, 18-panel pin-connected Pennsylvania through truss spans. In addition to the three main spans, the bridge would be approached by three 125-foot, 5-panel, pin-connected Pratt deck trusses on either end, which rested on 25-foot steel towers with deck girders. A later contract provided for the addition of eleven 40-foot deck plate girder spans, set onto steel towers, to be constructed on the west end of the bridge. Additional steel spans would be installed in the long approach trestle. On the west approach, a 68-foot deck plate girder span was installed to cross Angelica Street, as well as a 126-foot Pratt deck truss with 40-foot deck girder approaches to cross Ferry Street. The east approach would utilize a 175-foot, 7-panel, pin-connected Pratt through truss span to cross the Chicago & Alton Railway and the Wabash Railroad. The steel spans of the west approach viaduct were fabricated by Phoenix Bridge Company as part of a separate contract. In addition, the approaches utilized a combined 5,700 feet of wooden pile trestle, intended to be temporary until steel viaducts and earth embankments could be constructed. Work on the main portion of the bridge was completed in May 1890, and the bridge opened to traffic in December of that year.

During the Panic of 1893, the St. Louis Merchants Exchange gave up ownership of the bridge to the TRRA. Traffic steadily increased throughout the 1890s, and the need for a second track on the approach viaducts quickly became apparent. In 1902, the TRRA contracted with Massillon Bridge Company to strengthen the main spans of the bridge, and to construct a new west approach. Repairs to the 520-foot spans of the bridge included removing the stringers from the north track and doubling them up under the south track, placing heavier stringers for the north track and adding additional plates. Repairs to the 125-foot spans and 40-foot deck plate girder spans included the same type of repair as to the main trusses. In addition, a 60-foot, a 30-foot, a 95-foot, a 40-foot and eighteen 28-foot deck plate girder spans were constructed to replace the wooden trestle and 126-foot truss over Ferry Street. These spans would be constructed for two tracks, and set onto steel towers and concrete pedestals. In addition, eleven 28-foot double track deck plate girder spans would carry the northwest wye, leaving the structure near Ferry Street to connect to the Wabash. The east approach was replaced with a double track viaduct, consisting of twenty-six 28-foot spans, set onto steel towers and concrete substructures between 1909 and 1910. Much of the remaining wooden trestle was filled during the first decade of the 20th Century, and the Angelica Street and C&A/Wabash spans separated from the bridge. In 1910, the McKinley Bridge would open downstream, and the MacArthur Bridge would open in 1917. Despite the completion of two additional bridges across the Mississippi River, the Merchants Bridge would remain the critical railroad crossing of the Mississippi River at St. Louis.

Until the construction of this bridge, the Whipple design had been the preferred truss design for long spans. This bridge was believed to be Morison's first bridge utilizing the Pennsylvania design, and the first bridge with a curved top chord across the Mississippi River. Morison had completed a bridge with 520-foot Whipple through truss spans at Cairo, Illinois the year before, and was undoubtedly influenced by changing industry standards in the design of the Merchants Bridge. The Whipple design offered several disadvantages, and was succeeded by more economical and durable Pratt variants in the early 1890s. The Pennsylvania design became popular for long truss spans during the 1890s, eventually becoming the design of choice during the early part of the 20th Century. The Pennsylvania trusses on the Merchants Bridge would utilize heavily laced members, a tall truss web and a lattice portal, typical of spans designed by Morison. The approach deck trusses utilized an inclined endpost and were much lighter than the main spans. Deck girder viaducts were often used where an earthen fill was not acceptable, such was the case with the approach viaducts on this bridge. This design provided the cheapest and most durable design for lengthy viaducts.

During the 20th Century, the truss spans of George S. Morison gradually became obsolete. Several bridges designed by Morison would be replaced or removed. In 2004, the 125-foot deck truss spans on either end were replaced by new deck plate girder spans, set onto concrete piers. Further repairs were made to the main spans of the bridge at this time. By the mid-2010s, it had become apparent that the bridge was obsolete for modern traffic, with one train permitted on the bridge at a time, going a maximum 5 miles per hour. Construction on the west approach viaduct and northwest wye viaduct began in 2016, with the replacement of the remaining deck plate girder spans with a retaining wall and concrete box culverts. This work was completed in 2018. The east approach viaduct spans were replaced in the same manner between 2019 and 2020. The main truss spans of the bridge were replaced by new spans of a polygonal Warren through truss design between 2021 and 2022. The replacement project was completed in late 2022. The old trusses were moved downstream on barges, where they were disassembled. In addition to the replacement of all historic components of the bridge, the original stone piers were encased in concrete and retrofitted for greater seismic protection.

The replacement of this bridge resulted in a significant loss of American bridge history. The spans were offered for reuse, but were not taken, likely due to the size. In 2024, few bridges designed by George S. Morison remain throughout the United States. At the time of replacement, the bridge was in poor condition, and had long outlived its useful service life. The replacement of this bridge has doubled the capacity that the TRRA can operate over the Mississippi River at this location. The author has ranked the bridge as being nationally significant, due to the historic nature and large scale design of the structure.