Hawarden Railroad Bridge (North)

Located between Hawarden and Hudson, this through truss bridge carries a former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) line over the Big Sioux River. The previous bridge at this location was likely a wooden truss bridge, approached by timber pile trestle spans. In 1900, it was decided to rebuild the bridge with a steel truss span, set onto new stone piers and approached by timber pile trestle spans on either end. The approaches were reconstructed in approximately 2010, giving the bridge its present configuration. Currently, the bridge consists of a 138-foot, 6-panel, pin-connected Pratt through truss span, set onto stone piers. The south approach consists of 25 13-foot steel stringer spans, while the north approach consists of eight 13-foot steel stringer spans. Both approaches are set onto a combination of timber pile bents and steel pile bents. The timber pile bents were retained from the previous approaches, and were repaired with new concrete caps when the approaches were rebuilt. An unknown contractor fabricated the truss span, while it is unclear if railroad company forces or an unknown contractor constructed the stone piers.

The truss span follows a standard design used by the Milwaukee Road between approximately 1894 and approximately 1900. This span uses built-up members, a standard floor and a lattice-style portal. The top chord and endposts both consist of built-up beams, with X-lacing on the bottom and solid plates on the top. The bottom chord also consists of a built-up beam with X-lacing on both sides. The vertical members use a built-up design often used by the Milwaukee Road in the late 19th Century, consisting of two U-shaped channels connected by thin plates spaced throughout the beam. The diagonal members consist of rectangular steel eyebars. The floor system consists of two plate girder stringers, connected to plate girder floorbeams. The portal bracing uses a shallow double intersection lattice beam and rounded solid heel bracings without cutouts. The sway bracing uses a V-laced beam, which is connected to the vertical members by angled L-bar brackets. The upper lateral bracing is composed of rods, which are pinned to the top chord. The lower lateral bracing is composed of L-shaped bars. The approach steel stringer spans consist of four beams, arranged into two sets of two. Dressed masonry is used for the stone piers, which have a rounded rectangular shape. Stone for the piers has a tan color, and was quarried at an unknown location.

Pratt trusses were arguably the most common railroad truss bridge design during the second half of the 20th Century. This design was simple, economical and durable. By the turn of the 20th Century, railroads began switching to riveted Warren truss spans. The Milwaukee Road continued to use Pratt trusses until approximately 1910, when it followed suit in switching to Warren trusses. This style of span was one of several Milwaukee Road-designed spans constructed between 1890 and 1910. Shortly after this span was fabricated, similar spans began using heavier V-laced vertical members and deeper portal bracing. Since the initial fabrication, the truss span has seen no significant alterations. Additional repairs were made to the approaches after the March 2019 flood damaged several bents. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the truss design.