BNSF Mississippi River Bridge (Little Falls, North)

Located on the north side of Little Falls, this unique through truss bridge is the northern of two former Northern Pacific Railway bridges across the Mississippi River in the city. The first bridge at this location was constructed between late 1881 and early 1882 for the Little Falls & Dakota Railroad. This bridge consisted of two 160-foot wooden Howe through truss spans, set onto stone substructures. Timber trusses quickly became outdated for railroad use, and in 1891 the bridge was replaced by a heavier steel truss bridge, reusing the same substructures. It is believed the bridge was raised several feet in the early 20th Century, as part of the construction of a new dam downstream. On the night of May 10, 1974; a freight train derailed on the bridge, destroying the east truss span. In response, BN installed a secondhand through truss span, giving the bridge its present configuration. Currently, the bridge consists of a 160-foot, 6-panel, pin-connected Pratt through truss west span and a 160-foot, 10-panel, riveted Warren through truss east span. The entire bridge is set onto stone substructures with large concrete pedestals. The west span is original to the bridge, and was fabricated in 1891 by the Lassig Bridge & Iron Works. The east span was reused from an unknown location, possibly from a former Great Northern Railway line near Spokane, Washington. This span was fabricated in approximately 1900 by an unknown contractor. An unknown contractor constructed the stone substructures, while it is unclear if the concrete alterations were constructed by an unknown contractor or by railroad company forces.

The use of both light Pratt and heavy Warren through trusses give this bridge an unusual appearance. The west span consists of a standard NP pin-connected span, with light built-up members and a standard floor. The top chords and endposts of the west span consist of two channels, connected by X-lacing on the bottom and a solid plate on the top. The bottom chord uses two different designs, typical of bridges from this era. At the outer two panels, the bottom chord consists of two channels connected by X-lacing on both sides, while the center two panels consist of one set of eyebars. At the end panels, a built-up crash bar consists uses V-lacing on all four sides. Unique to this span, the outermost lower connections consist of a double connection, with one connection at floor level and the other connecting the crash bar and hip vertical. It appears that the bottom of the hip vertical is riveted to the bottom chord. The inner vertical members consist of X-laced channels, while the hip verticals consist of standard eyebars. All diagonal truss members consist of steel bars, with the counters using turnbuckles. The floor system uses a standard design, with two plate girder stringers and plate girder floorbeams, which are tapered at the ends. Both the upper lateral bracing and lower lateral bracing consist of steel bars, The portal bracing and sway bracing both use a standard NP design, with a lattice bar and decorative plates on either side. These plates are decorated with a ribbon of circle cutouts.

The east span follows a standard GN design from the turn of the 20th Century, with heavy members, riveted connections and a standard floor system. Both the top chords and endposts use a built-up design, with a solid plate on the top and X-lacing on the bottom. The bottom chord uses a similar design, with X-lacing on both sides. The diagonal truss members both use a heavy built-up design, with X-lacing on both sides. The vertical truss members consist of V-laced beams, with the exception of one member on the south side. The floor consists of two plate girder stringers, which are connected to plate girder floorbeams at the panel points. The lower lateral bracing consists of solid bars, which form an X-shape. Both the portal bracing and sway bracing follow a standard GN design, with a lattice design formed out of L-shaped bars. The upper lateral bracing consists of X-laced beams which form an X shape at each panel. Throughout the east span, many of the connections have been rebuilt with high strength bolts, and one vertical member on the south side has been replaced by a solid beam. The abutments use a standard design, with stepped wing walls, while the pier appears to follow a standard diamond shape. The concrete alterations include large concrete blocks on the top of the substructures. The stonework is heavily discolored, but appears to consist of a limestone.

Pin-connected Pratt trusses were the dominant railroad truss bridge design during the second half of the 19th Century. These spans were simple, economical and durable. By the turn of the 20th Century, riveted Warren trusses became popular, and largely superseded Pratt designs. These spans were more rigid, while not sacrificing economy or simplicity. It is unusual to see an example of both designs included in one bridge. Railroads often reused steel and iron spans, as it provided a cost effective way to build and repair bridges. While the practice reached its peak during the early 20th Century, railroads continued to reuse spans through the rest of the 20th Century and even into the 21st Century. Since the 1974 repairs, the bridge has remained largely unchanged. Today, it remains occasionally used to access Camp Ripley. Overall, the bridge appears to be in fair condition, with some deterioration to the substructure noted. The author has ranked this bridge as being regionally significant, due to the truss design and unusual history.