Phoenix Park Railroad Bridge

Located near the confluence of the Chippewa and Eau Claire Rivers at Phoenix Park in Eau Claire, this historic truss bridge was constructed to carry the Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) over the Chippewa River. It is believed that the first bridge at this location consisted of a wooden truss bridge set onto timber pile substructures, typical for bridges along Milwaukee Road branch lines. This bridge was likely renewed at least once in the 19th Century. By the turn of the 20th Century, traffic over this line warranted replacing wooden bridges with permanent structures. Because this was a branch line, constructing a bridge with new material was not a feasible option for the Milwaukee Road. Instead, it was decided to replace the bridge with iron spans taken from a recently replaced bridge. Work on the bridge began in 1903, and the structure was completed sometime in early 1904. The bridge was strengthened in 1941, and again sometime in the late 1970s. When the Chippewa River Railroad took over the line, this bridge was one of the main structures that needed upgrades that made continued operations unfeasible for the short line. After abandonment, the bridge was sold to the Wisconsin Department of Natural Resources, which later sold the structure to the City of Eau Claire for pedestrian use.

Currently, the bridge consists of a 232-foot, 16-panel, pin-connected Whipple through truss, approached by a 146-foot and a 148-foot, 10-panel, pin-connected Pratt through truss. The entire bridge is set onto concrete piers, which were constructed by railroad company forces. These trusses all include a number of features unique to this bridge. The trusses were reused from the first bridge across the Mississippi River between La Crescent, Minnesota and La Crosse, Wisconsin. Upon relocation here, the Whipple span was cut down from its original 250-foot length, and the two Pratt spans were cut down from 164-foot spans. The spans were cut down by removing one panel from each span, which reduced the length and likely raised the loading to acceptable levels. Originally, these spans had been constructed in 1876 by the American Bridge Company (of Chicago, Illinois). When the spans were installed here, the original floorbeams were replaced with secondhand beams originally fabricated in 1880 for Bridge #L-332 across the Mississippi River at Minneapolis, Minnesota. The mixing of different components from different spans is a somewhat unusual feature of this bridge.

All three trusses are constructed of wrought iron, and use light members and timber stringers. The endposts of all three spans use built-up beams, consisting of two channels and V-lacing on the back side. The top chord of all three spans consists of two channels, which are connected by thin plates throughout the length of the chord. The bottom chord of the spans is constructed of standard eyebars, typical for bridges of this era. The diagonal tension members use slender iron eyebars, while the counter members are constructed of iron rods, which are forged into loops at the ends. The vertical members of the spans use a unique rolled beam, which have a patent stamped on them. This patent concerns the unusual upper connections seen on this bridge. The vertical members were rolled at a mill in Trenton, New Jersey. The outermost vertical members on all three spans use slender iron bars. The Whipple span has been strengthened by applying longitudinal members and diagonal members at the end panels. The Pratt spans have been strengthened by adding additional channels around the outermost vertical members and adding a new diagonal member underneath the upper angle connection. The upper and lower angle connections use a separate "shoe" design, which connects the endposts to the top and bottom chords. Upper connections of the bridge are composed of a linkage with a hole drilled trough it, which is riveted to the channels of the top chord. These unusual connections were patented by Walter G. Coolidge and Edward Hemberle for the American Bridge Company in July 1874.

Upper lateral bracing of all three spans is composed of iron rods, which are connected to the top struts of the bridge. The lower lateral bracing is composed of square iron bars, which are looped at the ends and connected via pins at the floorbeams. The floorbeams of the bridge appear to have been modified and cut down, as evidenced by the remaining riveted ends on the south face of the bridge. The end floorbeams use an unusual thin beam, which has a triangular loop at the end, which loops around the lower angle connections. The stringers are each composed of four timber beams, which have been notched to allow for clearance at the lower lateral bracing. Portal and sway bracing on the two Pratt spans both use a transverse strut, connected by a standard bracket style bracing. The strut is placed on top of the top chords. The portal bracing on the Whipple span is much more unusual, using two transverse struts, connected by iron rods forming an "X". These iron rods are connected to the struts by pinned connections, and both rods have a turnbuckle near the middle. The top strut includes an integral hanger, which the rods are pinned into, while the bottom strut uses a linkage, with the rods looped around a pin, and the linkage pinned to the bottom strut at the endpost. The sway bracing of the Whipple span uses a similar design to the Pratt spans.

Since being relocated here, the bridge has seen a number of alterations. In 1941, the Milwaukee Road made a series of improvements to the spans to increase the loading capacity of the structure. These alterations included the addition to the longitudinal and diagonal members at the end panels of the Whipple truss, applying plates to the bottom flange of the endposts and top chords of all spans, adding additional channels to the outermost vertical members of the Pratt spans, adding an additional diagonal member underneath the upper angle connection of the Pratt spans and installing a fourth beam in each stringer. The new members of the bridge all were constructed of channels, connected by thin plates. Later additions included the repair of some lower connections of the Whipple truss span by using new plates and high strength bolts. Modifications in the 21st Century include the addition of a lighting system to the bridge, which allows the structure to be lit up in multiple colors.

Whipple truss spans were popular for railroad use in the 1860s and 1870s, before gradually declining in popularity during the 1880s. Also known as a "double intersection Pratt", this type of span was patented by Squire Whipple in 1847. Whipple trusses gained popularity with railroads seeking to construct longer spans of more durable materials. The main drawback of the design was the large amount of material required and the ambiguous stress distributions. As advancements were made in material development, large single intersection spans became a practical option for railroads. Pratt trusses were arguably the most popular truss design during the second half of the 19th Century, due to the durability and economy. These spans used a single intersection design, and were well regarded for their simplicity. Around the turn of the 20th Century, pin-connected spans fell out of favor for railroad use, as stronger rigid spans such as the Warren truss proved to be a better value. Wrought iron was a popular material for constructing bridges in the 1870s and 1880s. This material provided strength, while sacrificing economy. It is possible there is some cast iron in this bridge, particularly at the upper and lower connections. Material added during the 1941 strengthening is likely constructed of steel.

Railroads often reused iron and steel spans. Often, when a bridge was no longer acceptable for mainline use, it could be relocated to serve the needs of a branch line. Most railroads in the United States used this practice, as it saved money and did not require large amounts of new material. Lighter spans, such as the spans seen on this bridge, often were strengthened or partially rebuilt upon relocation. Some railroads, such as the Milwaukee Road, owned specialty shops for repairing and rebuilding steel and iron bridges. In addition, the Milwaukee Road used company forces extensively to construct substructures and erect bridges. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The bridge likely will need some minor repairs in the coming decades to ensure its survival for years to come. The author has ranked this bridge as being highly significant, due to the age and design of the spans. The bridge is now used as part of the Chippewa River State Trail, and is owned by the City of Eau Claire. The City of Eau Claire has recently listed the Soo Line S-Bridge on the State and National Registers of Historic Places, and is working to have the High Bridge listed on the National Register of Historic Places. The author believes that the Phoenix Park Bridge also should be given consideration for listing on the State and National Registers under Criterion C, as this bridge is a well preserved example of the period of construction and retains its original distinct features.