UP Rock River Bridge (Rockford)

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Located immediately upstream of the former Chicago, Burlington & Quincy Railroad bridge in Rockford, this large deck truss bridge carries the former Chicago & North Western Railway over the Rock River. The Galena & Chicago Union Railroad had reached the east bank of the Rock river in late 1851, and contracts were soon awarded for a new stone and timber bridge over the river. Work on the bridge progressed throughout 1852, with the first train crossing to the west side of the river in November of that year. The first bridge consisted of five 114-foot and two 99-foot Burr deck truss spans, set onto stone substructures. These deck truss spans were constructed entirely of timber, reflecting the dominant bridge building process at the time. It is believed that the stone for the substructures was completed by James Barr, who had the contract for constructing the G&CU. The Burr truss bridge lasted 17 years, until it was replaced by a new wooden Howe deck truss bridge in 1869. This Howe deck trusses used the same dimensions as the previous structure. These trusses were known as combination spans, and used iron tension rods to help strengthen the structure.

By the late 19th Century, wooden truss bridges had become obsolete, and the railroad moved to replace the structure. William H. Finley, Bridge Engineer for the C&NW designed a new metal deck truss span, and the contract for fabrication was awarded to the Wisconsin Bridge & Iron Company in 1895. Although the C&NW used lattice trusses near exclusively during the late 19th and early 20th Centuries, it was decided to use a riveted Warren deck truss pattern for the new bridge, likely due to the unusual lengths of the spans. Work on the bridge began in late 1895, and the replacement project was completed in 1896. The new trusses were erected by railroad company forces, and great care was taken to avoid interrupting service over the bridge. After the new bridge was complete, the old deck trusses were removed and cut up for scrap. It is believed that these spans were likely some of the last remaining wooden trusses on the Galena Division.

Currently, the bridge consists of five 114-foot and two 99-foot Warren deck truss spans, each with riveted connections and 10 panels. The truss spans are constructed of wrought iron, a notable feature of this structure. It was reported that the C&NW had experience getting better pricing for wrought iron truss spans, despite steel having been the dominant bridge building material for some time. Upon construction of the current bridge, the substructures were reconstructed as necessary, which generally involved removing limited amounts of stone. Typical of truss bridges from the era, members of the bridge are heavily laced, and the bridge utilizes a standard floor design. The two sizes of trusses are very similar to one another, with the only significant difference being the 99-foot spans utilize laced endposts. The only major alteration to the bridge since the construction is the addition of iron bands around the piers, which are intended to hold the stone together.

While Warren truss designs became the dominant truss bridge design in the 20th Century, the design was still relatively unused in the 19th Century. This design provided a simple and strong bridge, which was easily adaptable to any number of situations. The C&NW did not use many Warren trusses prior to 1930, as nearly all truss bridges utilized a lattice design. Despite this, a few such spans were designed by William H. Finley, although the design did not become popular with the C&NW until much later. It appear that the design may have been used sparingly, particularly for locations which were reusing stone substructures from unusual sized structures. Since the 1896 reconstruction, the bridge has seen only minor alterations, and still retains excellent historic integrity. Overall, the bridge appears to be in fair condition, with some deterioration noted to the substructures. However, the superstructure appears to be in good condition. The author has ranked this bridge as being regionally significant, due to the age, size and design.