Hawarden Railroad Bridge (South)

Located along 10th Street in Hawarden, this large truss bridge carries a former Chicago & North Western Railway line across the Big Sioux River in Hawarden. The first bridge here was likely a wooden truss bridge, constructed when the line was first built. In the early 20th Century, the C&NW made significant upgrades to this line, replacing timber bridges with steel and stone structures. In 1903, three stone piers and a stone abutment were constructed, and the following year three through truss spans were installed, retaining a timber pile trestle approach. Further upgrades were made to the bridge in 1913, when an additional thirteen deck plate girder spans were installed on new stone substructures, giving the bridge its present configuration. Currently, the bridge consists of one 145-foot quadrangular lattice through truss span, two 144-foot spans of the same design and thirteen 50-foot deck plate girder spans. The entire bridge is set onto stone substructures, which are constructed of yellow limestone likely quarried at Mankato, Minnesota. An unknown contractor fabricated the truss spans, while American Bridge Company fabricated the girder spans at their Lassig Plant in Chicago. Unknown contractor(s) constructed the stone substructures.

The truss span follows a design commonly used by the C&NW around the turn of the 20th Century, with heavier members, a standard floor and a utilitarian portal bracing. The top chord uses a built-up design, with V-lacing on the bottom and a solid plate on the top. The endpost uses a similar design, with an unusual X-lacing on the back side and a solid plate on the exterior. The bottom chord also is composed of built-up beams, with V-lacing on both sides. Similar to other spans of this design, the compression members are composed of V-laced beams of various designs, while the tension members use L-shaped bars. The floor system follows a standard design, with two plate girder stringers per track and plate girder floorbeams spaced at panel points. The portal bracing follows an A-frame design, which is constructed using V-laced beams. V-laced beams are also used for the sway bracing. L-shaped steel bars are used for both the upper lateral and lower lateral bracing. The deck plate girder spans follow a standard design, with two heavy plate girders and an open deck. All of the piers are similar in design, using a diamond shaped structure supported by timber piles. The abutments use stepped wing walls, which extend at an angle from the structure.

This type of truss design is relatively uncommon throughout the United States. However, a few railroads preferred the design, such as the Chicago, Rock Island & Pacific Railway (Rock Island), the Chicago & North Western Railway (C&NW) and the Chicago, St. Paul, Minneapolis & Omaha Railway (Omaha Road). Spans constructed in the late 1870s and early 1880s for the C&NW featured an arched and pedimented lattice portal bracing, light sway bracing and laced members. The second generation was nearly exclusively constructed by Lassig Bridge & Iron Works between 1884 and 1900, and featured heavier members and a decorative pedimented portal bracing. While the design fell out of favor for the Rock Island and Omaha Road around the turn of the 20th Century, the design remained popular with the C&NW into the 1920s. 20th Century versions of this design used significantly heavier members, were taller and contained no decorative features. 19th Century versions of this design were primarily constructed out of wrought iron, while 20th Century versions of this design were constructed of steel. The C&NW preferred this design, as it was both strong and demonstrated great resilience in case of a derailment. Since the 1913 construction, the bridge has seen no significant alterations, and remains in use. 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.