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This bridge consists of two large pin-connected Pennsylvania through truss spans and a slightly smaller truss that is a combination of a Pennsylvania and a Parker truss with multiple connection types. The truss spans are all at the northernmost end of the bridge. The southern end of the bridge has a long approach system. The original approach system was demolished a number of years ago and replaced with modern pre-stressed concrete spans. As such, the approach spans are no longer historically significant. However, the truss spans alone should be considered to have historic and technological significance. The remainder of this narrative will discuss the truss spans only. As will be discussed, one of the truss spans is truly unique, and of original, unaltered construction. The exact reason for this span's unusual design is not known but is believed to be related to a former railroad under the north end of the bridge. The unusual design likely allowed for the erection of the bridge with limited disruption to the railroad below. One might think the unusual design would be recorded in historical news articles. However this was not the case. Instead, it was a grade crossing with a different railroad south of the bridge that was created by the construction of this bridge which created enormous controversey, as that railroad opposed the addition of a new grade crossing on their line. Additional controversey was caused when the unions objected to the award of the contract for construction of this bridge to Dravo Construction Company, which was apparantly a non-union company. Neither the railroad or the unions had success in the courts however, and the bridge was constructed by Dravo and included the aforementioned grade crossing south of the bridge.
This bridge is a rare surviving example in Pennsylvania of a large pin-connected truss bridge. Pin-connected truss bridges once carried many of Pennsylvania's highways over the large rivers in the Commonwealth. At one time, Pennsylvania was one of the few states with a sizable population of pin-connected truss bridges crossing large rivers. Unfortunately, nearly all have been demolished or are in imminent danger of demolition. This bridge is thus today distinguished as rare. Similarly, bridges with a Pennsylvania truss configuration are, perhaps ironically, today extremely rare in Pennsylvania, again due to widespread demolition.
Despite carrying a relatively high volume of traffic, the bridge appears to retain good historic integrity with no major alterations to the overall design and materials of the truss superstructure.
This bridge should receive an extremely high preservation priority.
An Eastern steel brand was noted on this bridge.
Above: Eastern brand. Photo Credit: Patrick Gurwell.
Although the Pennsylvania truss spans are large and highly significant, the smaller truss span at the far northern end of the bridge needs to be singled out since it has one of the most unusual designs ever encountered in a truss bridge, and may be the only one of its kind in existence.
Trusses spans normally have a truss configuration that is symmetrical. However, this truss span is asymmetrical in its configuration. The northern truss span has ten "primary" panels. At first glance, it may appear that the primary panels on the northern half of the span are subdivided, following the Pennsylvania truss configuration, while the southern half is not subdivided and instead follows a Parker truss configuration. This alone would be strange enough. However the reality is even more unusual: only the four northernmost primary panels are subdivided in the manner of a Pennsylvania truss. The remaining six primary panels are all not subdivided, and thus follow the Parker truss configuration. In addition, the northern end post gets additional support not given to the southern end post with the inclusion of a vertical and diagonal member that connect to the mid-point of the end post.
Another extremely bizarre aspect of the bridge is the southern six panels of the truss have a bottom chord that is an eye bar, while the remaining northern panels all have an unusual, massive, riveted, built-up box beam. This is another asymmetrical detail where symmetry would be expected on a truss, however note that the asymmetry of the bottom chord aligns with the asymmetry of the truss configuration, which is no coincidence. This box beam bottom chord is riveted, although note that portions of the bottom and inside face of the beam have been altered with modern bolts present, apparently as part of a floor beam alteration, discussed below.
Since the northern four primary panels are subdivided by the Pennsylvania truss configuration, it would be expected that their would be additional floor beams under the northern four primary panels, with an extra floor beam present at each subdivision point. This may indeed be the way that the bridge was originally configured. However, this is the one area where alteration is present on the bridge. With the exception of the northern four primary panels, the floor beams on all the truss spans are built-up i-beams. However, the floor beams under these northern four primary panels have all been replaced with modern rolled beams. In addition, the modern floor beams are more numerous than would be expected, with extra floor beams present at places that are neither a primary or subdivided panel point. These extra floor beams simply run from bottom chord to bottom chord. While it is possible the original floor beams followed this highly unusual "extra floor beams" design, it seems more likely that one floor beam was present for each primary and subdivided panel point.
Another oddity of the bridge is that all of the diagonal members on the bridge are built-up beams except for two diagonals on each truss web, which are eye bars instead. This however is a symmetrical detail and while an unusual detail, does not appear to have anything to do with the above asymmetrical details.
Unlike the southern Pennsylvania truss spans which have largely traditional pin connections, the northern truss span has a hybrid of riveted and pinned connections. Some of these are the result of the unusual asymmetrical design, and/or areas where a combination of eye bar and built-up "beam" style members and chord are connecting. Eye bars require pins to connect, this is to be expected. In addition, built-up "beam" style members and chords usually riveted to gusset plates. So for example, where the eye bar connection connects to the box beam bottom chord, a combination of pin and gusset plate might be expected. There are also some connections on the northern part of the span's bottom chord, where no eye bars are present and the entire connection is a typical riveted connection with only gusset plate used. The top chord has a different detail, however. Even on the sections of the top chord where no eye bars are connecting with the top chord, a pin is present. The system works by having all the truss members riveted to a gusset plate. The gusset plate itself has a hole in it, allowing the pin to pass through through gusset plate, forming a pinned connection.
It also is worth considering why the four northern primary truss panels have all these unusual details, which remains somewhat of a mystery. When all the unusual details are considered as a whole they could have been designed to make the northern end of the truss span stronger than the rest of the span. A visit to this bridge quickly reveals why this may have been desired. The northern end of the bridge ends at a T intersection with a busy road. Northbound cars at the northern end of the bridge must brake, stop, and wait to turn, often resulting in a lineup of cars at the northern end of the bridge. Thus this span bears more live load for longer periods. Because of this, it would seem that the northern end of the span might wear out faster than the rest of the bridge if it did not have additional strength. The unusual details on this bridge might have been designed to maximize service life of the bridge by providing a bridge that would wear out uniformly, despite extra wear-and-tear at the far northern end. An alternative possibility for the unusual span design may lie in the fact that this span originally passed over a railroad line. Railroad involvement often resulted in unusual construction challenges because the railroad would certainly demand that during construction of the bridge service on the railroad line must not be interrupted. Perhaps the unusual design of this truss span somehow made it easier to build the span without disrupting railroad traffic. Exactly how this might be the case would require additional research, but it might have had something to do with trying to eliminate the use of falsework on the area where the railroad tracks were located. Simple truss spans like this were usually erected with falsework, but traffic could not be maintained on the railroad if falsework were built on the tracks.
A possibility that bears consideration when studying this bridge's unusual details (the panels with the Pennsylvania truss configuration and the built-up beam bottom chord on the northern four primary panels) is whether these could all be the result of an alteration from the bridge's original design. In other words, could this span have originally been a typical Parker truss with its entire bottom chord being an eye bar? This indeed could be the case, however it should be noted that both bottom chord and the additional members needed to form the Pennsylvania truss configuration are all riveted and conform to the "style and feel" of the bridge. If they are an alteration, an engineer took great pains to maintain the style of the bridge, and the alteration would have taken place before rivets ceased to be used in bridge construction. Furthermore, if it was an alteration, the alteration itself might be old enough to itself be considered historic, as an example of how engineers of the past used creative ideas to extend the life of a bridge, something sorely lacking in today's world of "demolish and replace." Finally, it is worth noting that if all these oddities are really an alteration, than this would be one enormous alteration. Indeed the extent of such alterations, which would likely have required extensive false work to support the truss during the alterations, is so great it seems to lack economy; it would seem as though the highway agency would have gone for replacing the whole span instead. Additionally, the later discovery of an undated historical photo which shows the unusual bottom chord and truss configuration intact, add weight to the argument that this span's unusual design is original to the bridge.
The northern four truss panels, with the massive box beam style bottom chord design, the Pennsylvania truss configuration, and even the altered floor beam design with extra floor beams between panel points, is all very similar to the design seen in this bridge in Ontario.
Pennsylvania is noted for having a historic bridge inventory that even when first created was unusually conservative in its findings for bridges eligible for the National Register of Historic Places. For example, unlike other states, the Pennsylvania Historic Bridge Inventory did not identify outstanding state standard plan truss bridges as eligible for being good representative examples of a period in history and the development of state standardized truss bridge technology in Pennsylvania. The Pennsylvania Historic Bridge Inventory is also today noted for being highly outdated, with PennDOT-managed inventory updates failing to adequately address the unparalleled and staggering rate at which historic bridges have been and are being demolished in the Commonwealth.
Regardless of these aspects of the inventory, the fact that the inventory not only found this bridge to be ineligible for the National Register of Historic Places, but said the bridge has "no unusual or noteworthy features" seems to be nothing short of absurd, given the issues HistoricBridges.org has presented in the above narrative. Indeed it is questionable that the reviewers for the Historic Bridge Inventory even took a brief look at this bridge. The only reference to the unusual details of the bridge is a statement that "The northernmost span has been altered by replacement of the lower chord eye bars with steel channels." It however is unclear that this riveted bottom chord detail is an alteration, especially since it seems to go hand in hand with the other oddities of the bridge (which the inventory discussion does not even mention), such as the panels with a Pennsylvania truss configuration. The discussion of the bridge also mentions bolted connections at the lower panel points which do not exist. All connections are either riveted or pinned. The discussion has errors and is incomplete, failing to justify why such an unusual bridge is
Worse, PennDOT's 2008 truss bridge update to the Historic Bridge Inventory, which apparently was supposed to update the inventory with additional eligible bridges to account for demolished bridges failed to find this bridge eligible for the National Register of Historic Places. The only comment in the update findings document was that the bridge was not the longest Pennsylvania truss in the state. No mention was made of the unusual details that HistoricBridges.org found on this bridge.
This bridge should immediately be reevaluated for potential National Register eligibility, in consideration of the unusual design details of the bridge.
After 2017: Recognized Historical Significance
It took almost another decade, but finally at long last, PennDOT had no choice but to recognize the significance of this historic bridge. The bridge is now formaly eligible for listing in the National Register of Historic Places as it should be. PennDOT now recognizes this with the following noted features:
-Uncommon design
-Regionally rare
-Exceptional overall
length
-Multiple spans
-Unusual combination of a Pennsylvania and Parker
truss with multiple connection types
-Artistic value: decorative portal and
portal bracing
This finding appears to have been well-timed as there have been hints that this bridge might eventually be at risk for demolition and replacement sooner rather than later.
Information and Findings From Pennsylvania's Historic Bridge InventoryDiscussion of Bridge The 24 span, 1,922'-long bridge consists of three, 263'-long, Pennsylvania thru truss spans built in 1914, and 21, 54'-long, prestressed concrete box beam approach spans built in 1987. The pin connected truss spans are traditionally composed of built up compression members and eye bar tension members. The northernmost span has been altered by replacement of the lower chord eye bars with steel channels and replacement of the pin connections with bolt connections at the lower panel points. The Pennsylvania truss, a variation of the Pratt truss with subdivided panels and polygonal top chord, was developed by bridge engineers of the Pennsylvania RR about 1875. This example has no unusual or noteworthy features. It is a late example of its type/design that has been altered. Earlier and more complete examples have been identified. The bridge is not historically or technologically distinguished by its setting or context. Discussion of Surrounding Area The bridge carries a 2 lane road and a sidewalk over a stream, floodplain, and an abandoned railroad line. At both ends, the setting is mixed use residential and commercial with buildings from the mid 19th to the late 20th century. The setting does not have the cohesiveness or integrity of a historic district. Bridge Considered Historic By Survey: No |
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