MacArthur Bridge Approach Viaduct (Southwest)

View an article discussing the construction of this viaduct

During the 1890s, the Terminal Railroad Association of St. Louis (TRRA) was growing in power, owning both the Merchants Bridge and the Eads Bridge, the only crossings of the Mississippi River at St. Louis. Because the TRRA owned both bridges, the TRRA could set tariff rates for freight and passengers crossing the Mississippi River at St. Louis. During the early 20th Century, the City of St. Louis desired a "free bridge", which would provide toll free passage of railroad and roadway traffic across the Mississippi River. A Municipal Bridge Commission was formed in 1905 by the Mayor Rolla Wells to study and construct a toll-free crossing of the Mississippi River. A bond issue was voted on in 1906, authorizing money to construct the bridge.

In 1908, acquisition would begin on the right-of-way for the bridge. After a rejected design, it was decided to construct the main bridge with three large main spans, with a double track railroad deck on the lower portion of the bridge and a roadway portion on an upper deck. A series of viaducts would need to be constructed to the bridge to allow railroad and roadway traffic to use the main spans. The main bridge would utilize three large through truss spans to cross the Mississippi River near Chouteau Avenue. With a 677-foot main span, these spans were the highest, longest and heaviest constructed at the time. Construction on the main bridge was started in late 1909, and completed in 1912. The American Bridge Company was contracted to provide the steel for the bridge, with the Missouri Valley Bridge & Iron Company constructing the main stone piers. Until approach viaducts could be constructed, the bridge could only be utilized by pedestrians, which had to climb stairs at either end and utilize a wooden deck on the railroad deck to cross the river. The west approach viaduct would be completed in 1913, and the east approach viaduct would be completed in 1917. Due to stalled negotiations between the railroads and the City, railroad traffic would not utilize the bridge until 1928.

To help attract railroad traffic, a series of supplemental viaducts were planned on both the east and west approaches. As originally built, the bridge connected to the St. Louis Terminal Railroad yard on the west end, and to the Alton & Southern Railroad yard on the east end. While the bridge and viaducts crossed a number of other railroads, it was difficult to encourage these railroad companies to use the bridge without providing additional connecting viaducts. The first viaduct planned would be the southwest viaduct, which would provide a connection to the Missouri Pacific Lesperance Street yard, the Manufacturers Railway, and the TRRA-owned St. Louis Terminal Railway. Preliminary survey work began long before construction began, due to the complex alignment required for the structure, which would cross city streets and industrial areas.

Contracts for the construction of the viaduct would be awarded to American Bridge Company for the superstructure, Dunham Construction Company for the substructure and Ben Hur Erection Company for the erection of the structure. C.E. Smith was in charge of designing the structure. The viaduct would leave the main structure immediately west of the main spans, swinging to the left for 1,600 feet; before coming to a short tangent section, and curving right on a 6.5-degree curve. The curve beginning at the main spans would be a compound curve, using sections of 12-degree, 8-degree and 5-degree left hand curves. Much of the alignment was determined based on existing infrastructure below, such as industrial buildings, railroad yards and city streets. The survey work for this viaduct was complex, requiring offset points located on curves. Locating the substructures for the bridge proved to be difficult, and the viaduct would require many unusual sized pieces. Unusual towers were required to avoid obstacles, further raising the cost of this bridge. Work on the viaduct began in 1928, and would be completed in early 1929. Since the initial construction, there have been no significant alterations to the structure.

The viaduct mainly consists of deck plate girder spans, supported by steel towers, set onto concrete pedestals. Much of the northern portion of the bridge is both skewed and on a significant curve. Beginning at the main bridge, the bridge consists of an 80-foot clear span and a 16-foot tower span (bents #S1 and S2) where the tracks leave the west approach viaduct. The viaduct then curves, using clear spans of 70 feet, 85 feet, 102 feet and 85 feet, set onto towers with spans of 50 feet (bents #S3 and S4), 55 feet (#S5 and S6) and 70 feet (#S7 and S8). The southernmost 70 and 85-foot spans are constructed with a flare, on account of the curve. The southern track uses shorter 65-foot spans. The towers were constructed with sufficient clearance underneath, to allow for tracks of the TRRA. These towers use heavy bracings in the upper portion of the tower, and are significantly larger than normal towers. The 70-foot span continues to cross an active TRRA line, with the 102-foot span crossing 1st Street, and the last 85-foot span crossing Chouteau Avenue. An unusual 9-panel riveted Pratt deck truss crosses an industrial building at the corner of Chouteau Avenue and 1st Street. The western truss line is 120 feet long, while the eastern truss is only 110 feet long, due to the curve. This span is set onto bents #S9 and #S10. The truss span utilizes a heavy design, with solid members and a shallow depth. The shallow span was required due to the building underneath, and is an unusual feature of this bridge. The floor of the truss span is constructed of heavy laced members. Bent #S9 is a standalone steel bent, which utilizes a pinned connection near the top of the bent.

After crossing the industrial building, the bridge uses clear spans of 70 feet, 80 feet and 50 feet, supported by tower spans of 25 and 50 feet (bents #S10, S11 and S12), 45 and 60 feet (bents #S13, S14 and S15) and 75 feet (bents #S16 and S17). Bents #S13, S14 and S15 form an unusual skewed bent, where the west track is considerably longer. Three 100-foot through plate girder spans cross a former coal yard of the Missouri Pacific Railroad. These spans are heavily skewed and curved, and are set onto concrete piers. A 68-foot, an 85-foot, a 60-foot tower span (bents #S23 and S24), and a 90-foot deck plate girder span cross the former Missouri Pacific, now Union Pacific. The 60-foot tower span is arranged diagonally across the tower, which was constructed to allow for railroad traffic below. A 60-foot through plate girder span crosses Rutger Street, and the remainder of the bridge is made up of sixteen 70-foot deck plate girder spans and twelve 30-foot tower spans, set onto a tangent section. The approach then uses a retaining wall to reach ground level.

Because of the location, the bridge features several unique features. The use of different sized structures in a span is an unusual construction method, typically only used for sharp curves. The deck plate girder and tower design allowed for these unusual variations. The use of a shallow deck truss is also unusual, as this design was rarely used, and almost exclusively for unusual circumstances, such as to cross a building. These types of spans require much heavier members than traditional deck truss spans. While much of the main MacArthur Bridge structure has been replaced, this viaduct has seen little alterations. Overall, the viaduct appears to be in fair to good condition, with no significant deterioration noted. The author has rated the viaduct as being regionally significant, due to the unique designs seen throughout the structure.