CIC Iowa River Bridge (South)

Located on the south side of Iowa City, this mismatched through truss bridge carries a former Chicago, Rock Island & Pacific Railroad (Rock Island) branch line over the Iowa River. Little is known about the history of this unusual bridge. Originally, the two piers and abutments were constructed in 1870 for use for the Keokuk, Iowa City & Minnesota Railroad (KIC&M); a proposed line that would have connected St. Louis, Missouri to Duluth, Minnesota. Originally, the superstructure of the bridge was supposed to be installed in early 1871. However, financial difficulties led to the project being abandoned and the KIC&M becoming defunct. The substructures remained unused until 1879, when the BCR&N purchased the site and finished the structure. The first bridge installed here consisted of two 155-foot and one 170-foot, 10-panel, pin-connected wrought iron Warren through truss spans, fabricated by the Louisville Bridge & Iron Company. It is unclear if this bridge was altered in the 19th or early 20th Century, although a 1930 report on bridges across the Iowa River indicates the bridge only had two truss spans at that time. It is also unclear if these two truss spans were from the 1879 bridge, although a 1933 newspaper article claims the original 1879 bridge was still standing. It is believed that the present structure was constructed from secondhand material in approximately 1930. Currently, the bridge consists of a 155-foot riveted quadrangular lattice through truss span (north span), a 155-foot, 6-panel, riveted Warren through truss span (south span) and several timber pile trestle spans on the south end. The entire bridge is set onto stone substructures, which have been capped with concrete; while most of the south approach is set onto timber pile bents.

The north truss span is believed to have been fabricated in approximately 1885 for use at an unknown location. This span follows a standard design for lattice trusses constructed for the Rock Island, with light members, a light floor system and attractive pedeimented portal bracing. It is believed that the truss is fabricated from wrought iron, a typical bridge material for the era. The top chord is composed of a built-up beam, constructed from two U-shaped channels joined by a solid plate on the top and widely spaced metal strips on the bottom. The endpost also uses a built-up design, consisting of two channels connected with a solid plate on the exterior and widely spaced thin plates on the interior. The bottom chord is lightly constructed, consisting of two parallel T-shaped plates and no bracing. Typical of lattice truss spans from this era, the diagonal members are formed from a number of different designs. The outermost compression members use solid beams, while the inner compression members consist of built-up beams formed from two L-shaped bars connected by widely spaced V-lacing. All of the tension members consist of L-shaped bars, and an X-laced crash bar is present at the ends of the truss. The floor system is traditionally composed, consisting of two light stringers and shallow notched plate girder floorbeams, which are set onto the bottom chord. Both the lower lateral bracing and upper lateral bracing are composed of light L-shaped bars. The portal bracing follows a standard Lassig Bridge & Iron Works design, with a pedimented lattice beam and a solid plate in the center. At the corners, the portal bracing was once connected to the endposts by triangular plates with decorative cutouts. However, this heel bracing was cut away at some point in the 20th Century. Also typical of these types of trusses, the sway bracing is constructed of simple square bars, set above the top chord.

The south truss span is believed to have been fabricated in approximately 1905 for use at an unknown location. This span follows a standard Rock Island design, with heavy members, a standard floor system and lattice style portal bracing. Both the top chord and endposts consist of heavily constructed members, built of two U-shaped channels connected by solid plates on the top/exterior and V-lacing on the bottom/interior. The bottom chord is constructed using two U-shaped channels, connected by widely set V-lacing on both sides. The vertical members are constructed of solid beams, while the diagonal members are composed of built-up beams which use V-lacing on both sides. The floor system is composed of heavy plate girder floorbeams placed at the panel points and two heavy plate girder stringers. The portal bracing uses a standard Rock Island design, consisting of a lattice design with four "X"s. At the corners, a triangular heel bracing with a rounded edge connects the bottom of the portal bracing to the endposts. The sway bracing uses a similar design to the portal bracing, with three "X"s and no plates at the vertical members. The upper lateral bracing is composed of light V-laced beams, while the lower lateral bracing is constructed of L-shaped bars. The south approach consists of standard open deck timber pile trestle spans, which reused the original south abutment. Both piers use a standard diamond shape, and both abutments use a standard design with stepped wing walls. All four of the stone substructures have been capped with concrete, and both piers have been reinforced with concrete around the base.

It is unclear which contractors fabricated the superstructure, although similar spans are known to have been constructed by prominent bridge firms. The lattice truss span was possibly fabricated by the Lassig Bridge & Iron Works, although this firm often placed builders plates on the endposts. The Warren truss span was possibly fabricated by the American Bridge Company, but a plate also would be expected on the endposts of this span. The stone substructures were constructed by John Wilson, a contractor hired by the KIC&M. It is unclear if the concrete portions of the substructures were constructed by railroad company forces or by an unknown contractor. Railroads often reused steel and iron spans, as it provided a cost effective way to rebuild and replace bridges without requiring large amounts of new material. Often, when a mainline span was replaced, it could still feasibly be repaired and reused for branch line use. The Rock Island frequently moved bridge spans between different locations to save money. Since both spans use standard designs and it is unclear when they were erected, blueprints or other railroad documents likely will be required to confirm the history of these spans. Dozens of standard lattice and standard Warren spans were replaced and reused by the Rock Island in the 1930s and 1940s.

The quadrangular lattice through 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). The Rock Island began using the design in the early 1880s as an alternative to iron pin-connected spans. Spans constructed in the 1880s and 1890s used lightly built-up members and a decorative pedimented portal bracing. At the turn of the 20th Century, the Rock Island constructed a handful of significantly heavier trusses of this design, before switching to more traditional single intersection designs. The main detraction of the design was its statically indeterminate nature, although the design performed well in case of a derailment. After lattice trusses fell out of favor, the Rock Island switched to using standard Warren truss designs, such as the south span of this bridge. This design was economical, strong, simple and easy to construct. Since the initial construction, the bridge has seen some minor alterations, including the removal of the heel bracing on the north span, encasement of the lower portions of the piers in the 20th Century and renewal of the south approach spans. Today, it remains in use as part of the Cedar Rapids & Iowa City Railway branch line to Hills. Overall, the bridge appears to be in fair condition, with no significant deterioration noted. The author has ranked this bridge as being regionally significant, due to the unique design and unclear history.