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The Tyrone Forge Viaduct is an early and rare example of a continuous t-beam bridge in Pennsylvania, and is considered eligible for listing on the National Register of Historic Places for that reason as indicated in the Historic Bridge Inventory. It is further noteworthy as an excellent and uncommon example of a curved t-beam bridge in Pennsylvania, as well as for the incorporation of superelevation and a significant 5.4% grade into the bridge design, representing a more complex engineering effort. The bridge is composed of seven t-beams spaced 6.1 feet apart. The bridge is a visually attractive structure, with its gracefully curved beams and its concrete railings that are shaped to match up with the decorative column design incorporated into the piers. The railings also have a simple pattern of incised vertical lines on the solid concrete parapet. As originally built, the bridge was composed of two sets of two-span continuous structures, forming a four span complete bridge. This can be seen in the original plans for the bridge which show an expansion bearing only at one end of the bridge and one in the middle. All other bearings are fixed.
In 2010, PennDOT began a comprehensive rehabilitation of this historic bridge to correct deficiencies in the structure, improve function and safety on the bridge, and to preserve the historic character of the bridge. The exemplary rehabilitation of this historic bridge is a win-win scenario that preservationists, PennDOT, and the general public can all appreciate and be proud of.
The rehabilitation of the Tyrone Forge Viaduct demonstrates how good planning and design, as well as some compromise can lead to a successful preservation project. For the sake of safety and the longevity of the structure, there were some alterations that had to take place as part of the rehabilitation. However, PennDOT worked to minimize the affect these alterations have on the historic integrity of the bridge.
Most notably, the original railings on the bridge were removed and replaced with new barriers that are slightly thicker and provide greater protection for vehicles. However, the replacement barriers were designed to replicate all the architectural treatment found on the original railings, including the pattern of vertical incised lines as well as the shaped design on the sections above the piers. This attention paid to maintaining the existing design of the historic railings on a replacement railing system is something that is often overlooked in rehabilitation projects. The fact that PennDOT chose to replicate this railing design speaks very highly of the quality of this rehabilitation and preservation project. It also was a very important step in ensuring that the aesthetic value of the bridge remains. Because of the relatively simple structure type that the Tyrone Viaduct is, the railings play a larger role in defining the aesthetic quality of the bridge than they might in other more complicated structure types such as a metal truss bridge.
Another significant alteration involved the center pier on the bridge. The National Bridge Inventory ratings for this bridge pointed to serious issues with the substructure, and this center pier may have been partly responsible for those low ratings. As such, significant work was needed here. This pier was the location of one of the two expansion bearings on the bridge. The rehabilitation plans called for the conversion of this expansion bearing into a fixed bearing, effectively turning the bridge into a single four span continuous structure instead of two two-span continuous structures. Also, the plans called for the encasement of the center pier in concrete following repairs to the existing pier. These repairs do change the design and appearance of the bridge slightly, but because these changes are limited to a single pier, and also considering the poor prior condition of the pier, these changes are an excellent compromise given the benefits they provide.
A final alteration made to the bridge as part of the rehabilitation is not significant in terms of the historic integrity of the bridge, but is worth mentioning simply to document the original design of the bridge, as well as for the sake of demonstrating how creative solutions can make a rehabilitation project feasible. The bridge originally had a small sidewalk on one side of the deck. The location that the bridge is in does not see much pedestrian traffic today and the sidewalk really was not needed. As a result, in order to provide wider lanes for vehicular traffic, the sidewalk was eliminated and the space was incorporated into the vehicular traffic lanes.
Other rehabilitation work included repair of the concrete superstructure using a routine method of removing the bad concrete, cleaning the area, coating any exposed reinforcing rbars with epoxy paint, and reinstalling concrete to the area, making sure to follow the original contours and design of the bridge. When sections of concrete were being repaired, plans specified the placement of new reinforcing bars in areas where the original bars were broken or had 25% loss of section. The rehabilitation of the bridge also included deck replacement, which involved removing the asphalt wearing surface and removal of a portion of the original deck using the very effective technique of hydrodemolition to carefully remove the old concrete and prepare it for the installation of new concrete.
In conclusion, the rehabilitation of this bridge by PennDOT is an excellent model of a good well-planned preservation project that hopefully will inspire similar projects elsewhere in Pennsylvania. The rehabilitation of this bridge corrected structural deficiencies, increased the safety features for traffic on the bridge, and preserved the historic value of the bridge. PennDOT deserves to be thanked for choosing to preserve this historic bridge.
Information and Findings From Pennsylvania's Historic Bridge InventoryDiscussion of Bridge The skewed, superelevated, 245'-long, T beam bridge built in 1937 is composed of 2, 2-span continuous spans. It is technologically and historically significant as an early example of the continuous design applied to T beam bridges. The bridge was designed by the state highway department and built by a local contractor. The continuous haunched beams reflect a structural need for deeper beams over the piers where the negative moments were greatest. Discussion of Surrounding Area The bridge carries a two-lane road on a grade with shoulders and a sidewalk over a two-lane state road and stream just northeast of the village of Ironville. A Conrail (formerly Pennsylvania Railroad) stone arch bridge crosses the same water feature just south of the bridge. An active stone quarry and yard is at the northeast quadrant. Bridge Considered Historic By Survey: Yes |
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