This bridge is a highly significant historic bridge, as one of the only known surviving multi-span bridges built by the Columbia Bridge Works, and the only through truss example in Western Pennsylvania. The Columbia Bridge Works is noted for its early, extensive use of rolled i-beams, unusual composition of built-up beams, and unusual connection details that set their bridges far aside from the "average" pin connected truss bridge. The Carlton Bridge is an excellent example of the company's work that displays many of these details. The bridge retains the company's beautiful distinctive builder plaque as well.
Each span of this double-span bridge is composed of nine panels. This bridge retains good historic integrity, including original lattice railings, builder plaques and decorative finials, although some of those have gone missing.
Preserving this bridge is important not just because of its historic value, but also for its beauty. Metal truss bridges sometimes are described as "industrial" or "utilitarian" but these observations are made by those who fail to really look at the bridge. Take a close look at this bridge and see the delicate, intricate beauty of its lightweight members that combine with v-lacing on built-up beams to form a unique geometric art that only a historic truss can display. Time has taken its toll on this bridge, but that which time has ravaged could be repaired or replicated. For example, the remaining beautiful finials that topped off the bridge could be used as patterns to make replicas and replace the missing finials.
A third party has stepped forward to relocate and preserve this bridge in New Jersey. The bridge will be preserved on private property, but in a location visible to the public. More details will be coming in the future.
Despite the value of this bridge and the potential for preservation, PennDOT decided to replace this bridge. This replacement could have been avoided, and given the significance of the bridge, great effort should have been made to preserve the bridge.
HistoricBridges.org was a consulting party for the Section 106 Review for this bridge. It is the belief of HistoricBridges.org that the reason that that this bridge is to be demolished and replaced is because PennDOT did not seriously consider as many alternatives as it could during the Section 106 Review. Further, there is a continuing unwillingness by PennDOT to leave a historic bridge standing next to its replacement. Finally, the consultants that PennDOT allows to conduct the Rehabilitation Feasibility Analysis might meet the basic requirements of PennDOT, but do not have a truly good portfolio of past work successfully rehabilitating historic metal truss bridges. The result is that the analysis makes preservation seem more difficult, less effective, and more costly than it really should be.
HistoricBridges.org had a particular concern with the conduct of Section 106 for this bridge. Once adverse effect of replacement had been established, the consulting parties were not invited to comment on proposed mitigation, something that they have a right to as consulting parties. HistoricBridges.org found out about the proposed mitigation only by chance while browsing a database and proceeded to submit comments. The problem with the proposed mitigation is that it failed to be substantial enough to truly mitigate the loss of such a rare and significant bridge. PennDOT did revise the mitigation later, however the revision merely was not much of an improvement. PennDOT's apparent belief is that "recording" the bridge or producing publications about historic bridges mitigates the loss of a bridge like the Carlton Bridge. While such productions may be useful, how does this mitigate the loss of a rare example of the Columbia Bridge Works? HistoricBridges.org believes that mitigations should have included preservation of some of the original bridge, perhaps saving a single span and putting it on display, even if just set on the ground as an exhibit, in a park or other public setting.
Information and Findings From Pennsylvania's Historic Bridge Inventory
Discussion of Bridge
According to the inspection file, the stringers and deck were replaced in 1990. The changes are minor modifications that do not affect the integrity of the truss.
Bridge Considered Historic By Survey: Yes
Information From www.mercercotrussbridges.com Demolition Mitigation Website
Discussion of Bridge
The Pratt Through Truss bridge features the distinctive, idiosyncratic details of its fabricator, the Columbia Bridge Works of Dayton, Ohio. Company trademarks include the extensive use of I-beams and bolted connections, such as those on the lower chords, which the company called lap-jointed "Flat Bar Chords." The company's designs reflect the experimentation that characterizes early truss bridge designs.
The Columbia Bridge Works of Dayton, Ohio was established in 1852 by David H. Morrison (1817-1882), Dayton's first city engineer. Morrison ranks among the earliest engineers to recognize the possibilities of metal truss bridge technology, establishing one of the first bridge companies in the nation, and reportedly building the first all-iron bridge west of the Allegheny Mountains. The firm specialized in Morrison's patented designs, the most successful of which was a bowstring arch-truss built throughout the Midwest in the 1860s and 1870s.
In the early 1870s, the Columbia Bridge Works began to produce variations of the Pratt truss design. Like many bridge builders of the period, Morrison developed a number of distinctive, idiosyncratic details. Trademarks were the extensive use of I-beams, which Morrison correctly believed to be an ideal shape for primary members, and bolted lower chord connections that Morrison called lap jointed "Flat Bar Chords." He claimed that the chords increased stiffness and reduced vibrations from large moving loads. Morrison passed away in 1882, but his company continued under the direction of his son, Charles Carroll Morrison, who had joined as a partner in 1868. The company remained in operation into the 1890s.
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