Carpentersville Railroad Bridge

Once located across the Fox River in Carpentersville, this historic through truss bridge carried a Chicago & North Western Railway spur to serve the Illinois Iron & Bolt Company, which operated a sprawling facility on both banks of the river. The first bridge at this location was constructed in 1879, and consisted of a lengthy pile trestle. By the 20th Century, this bridge had become outdated for railroad traffic, and the narrow clearance between bents proved costly to maintain. Reconstruction of the bridge was authorized in 1924, and completed in March 1926. As part of the work, the railroad installed a secondhand truss span and six new steel stringer spans, and rebuilt the remainder of the bridge in kind. New timber pile piers would be constructed for the steel spans. The truss span consisted of a 98-foot 9-inch riveted quadrangular lattice through truss span, originally fabricated in approximately 1880 at an unknown location. This span utilizes features typical of early quadrangular lattice through truss spans, and was likely fabricated by the Leighton Bridge & Iron Works, which constructed a number of lattice spans for the C&NW. The steel stringer spans were arranged into two groups, with two 36-foot spans located immediately west of the truss, and the remaining four located over the western channel of the river. The bridge consisted of a curve at the west end, which resulted in the western set of steel stringers utilizing a heavy skew.

While a few other railroads, such as Union Pacific, Rock Island and Erie all used the quadrangular lattice through trusses at various times, no railroad relied on the design as much as the C&NW. Between 1878 and 1930, through trusses constructed by the C&NW nearly exclusively used this design. Although lattice trusses were not popular with American railroads after the 1880s, the C&NW relied heavily on this design, as it had proven to be resilient towards derailments and damage. The main drawback of the design was the unpredictable nature, as the structure was not statically determinant. Despite this, numerous examples of this design continue to serve traffic today. The lattice truss design appears to have first been introduced to the C&NW by Leighton Bridge & Iron Works, which constructed some of the first iron lattice trusses for railroad use. Early designs of this truss utilized members constructed with angle bars, with compression members constructed of tightly laced angle bars. These early designs also used boxy endposts and upper chords, and a portal consisting of an arched lattice, with lattice heel bracings. After Leighton sold the company to Alden and Lassig Bridge & Iron Works in 1881, this company continued to produce a modified version of the design, using a pedimented lattice portal. In 1886, John Alden and Moritz Lassig split partnership, and Lassig Bridge & Iron Works continued to construct the design. Spans constructed from approximately 1885 until the mid-1890s utilized heavier members, a pedimented portal bracing with lattice on the sides and decorative cutout heel bracing. 20th Century versions of this design included much heavier members and heavily constructed portals with no decorative features.

The bridge at Carpentersville was an excellent remaining example of the earliest generation of the quadrangular lattice through truss design, constructed between approximately 1878 and 1883. Upon relocation, the bridge received some alterations, including the apparent replacement of the original stringers. While the original location of the truss is unknown, the unusual size may give some clues to its origins. Annual Reports of the Chicago & North Western Railway indicate that a 98-foot 9-inch truss was built at Peshtigo, Wisconsin in 1881. In a period between 1875 and 1885, this was the only span of this size listed in these reports. While other truss spans of this size may have been constructed, the C&NW seemed intent listing major iron bridges constructed each year. It is believed that the Peshtigo Bridge was replaced sometime in the early 1920s, which may provide further evidence to its reuse here. Research on the original location of this span is ongoing.

As a spur bridge, this bridge received relatively little maintenance. Timber components of trestle bridges generally need to be replaced on a regular schedule. It is likely that the timber components of the bridge were last updated in the 1940s or 1950s. By the late 20th Century, the bridge had begun to significantly deteriorate. Flooding, ice and age had all weakened the substructures and timber stringers of the bridge. High water in 2012 or 2013 caused the pier between the middle of the eastern two stringers to collapse, sending the spans into the water. All of the timber piers contained significant structural deterioration, with piers #6 and #7 under the west approach partially collapsing. The eastern two piers holding the truss had significant rotting of nearly all piles, and some piles which had collapsed. Due to concerns about the structural integrity and the impending removal of the dam upstream, the bridge was demolished in early 2024. At the time of demolition, the bridge was in exceptionally poor condition, and on the verge of failure. Rotted timbers in the piers were causing steel spans to shift and tilt, distorting the truss span in particular. In addition, the floor of the truss span had severe section loss at locations which were reconstructed in the early 1920s. While there had been some community involvement asking for the preservation of the truss span, deterioration to the span and substructures it rested on likely made it unfeasible and unsafe to attempt reusing the span. The author has ranked this bridge as being highly significant, due to the age of the truss.