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Additional Note: There is a possibility this bridge span was relocated from the Penns Creek Selinsgrove Bridge in Snyder County, Pennsylvania. It was built in 1905 for $65,000; moved about 1/4 mile north 1928; replaced 1941-3 after the south span collapsed in 1943 after being struck by bulldozer on trailer, necessitating replacement.
This bridge was an important historic bridge considered eligible for the National Register of Historic Places. At the time of its demolition, it was the last remaining pin-connected highway truss bridge in Forest County, and one of the only remaining truss bridges of any kind in the county. As such, it was a regionally rare bridge type. On a statewide basis, the bridge was also noteworthy as an uncommon example of one of a shrinking number of remaining pin-connected Parker truss bridges in Pennsylvania. The bridge was constructed in 1905, and relocated to the Lynch Village site in 1948.
The truss bridge was configured as follows, with approximate measurements accurate within 1/2 inch. Top chord and end post: back-to-back channels with v-lacing and cover plate (20.5 inches wide, 15 inches deep), bottom chord: paired up-set eye bars, vertical members: back-to-back channels with v-lacing on each side (17.5 inches by 10 inches), outermost diagonal members: up-set eyebars (5 inches wide), other diagonal members: back-to-back channels with v-lacing on each side, struts: two paired angles with a single road of lattice, sway bracing: horizontal paired angles, with a star pattern of riveted angles between this and the strut, Floorbeams: rolled American standard beams, deck: open metal grate, railing: traditional lattice mesh 36.5 inches in height with modern Armco style guardrail added.
The bridge had unusual detail, which was the composition of the diagonal members. With pin-connected truss bridges that have a configuration based on the Pratt, diagonal members are in tension, and as such normally eyebars (economical and well suited for tension) were employed for diagonal members. However with the Lynch Bridge, only the outermost diagonal members are eyebars. All the other diagonal members use a built-up beam design that was common for compression members like verticals, that being back-to-back channels with v-lacing. Indeed, these diagonal member beams on the Lynch Bridge are identical in design to the bridge's vertical members. It is not known why this variation is seen in the Lynch Bridge.
Another unusual detail with the diagonals is that there are no counters present. While not unheard of, this is a relatively uncommon occurrence. It is likely that the heavier diagonal members did not require or would not benefit from the presence of counters.
Like so many historic bridges in the Commonwealth, PennDOT elected to replace and demolish this historic bridge with any possible preservation solutions for this bridge being discarded. Initially one has to wonder if a full two-lane replacement bridge was really needed in a county that is so rural that it doesn't even have a single stop light. Surely a rehabilitated Lynch Bridge would have been sufficient for the traffic of the area. However, setting this preservation solution aside, there still were numerous alternatives to turning this historic bridge into a pile a scrap metal.
Although an unsuccessful attempt was made to market the bridge to a third party for preservation, PennDOT didn't have the guts to stand up and realize that a third party should not be required to take ownership and preserve the bridge in order to prevent demolition, and that if marketing is unsuccessful, PennDOT could instead simply abandon the bridge as a historic ruin, or leave it open to non-motorized traffic. Other states in the United States have done this, and there is no real justifiable reason why Pennsylvania could not as well. The replacement bridge was built on new alignment and not in the way of the historic bridge. Demolishing a historic bridge that is not in the way of its replacement is among the most senseless and wasteful things that can be done to a historic bridge. Essentially, tax dollars are being spent for no other reason that the goal of wiping a beautiful historic bridge off the face of the earth.
Sometimes, concerns are voiced that if the bridge is left in place, it might collapse later. However, once vehicular traffic is taken off the bridge, it can be amazing how long a bridge will stay standing with no further work done to it. A serious analysis of this is not being considered by PennDOT. Further, many years down the road when metal truss bridges become even more rare and public awareness increases, the opportunity for a full restoration of the bridge might then present itself, which would eliminate that risk of collapse in the future. Further, if after 20 years of abandonment the bridge does show signs of sudden collapse, and nobody wants to preserve it, the bridge can be removed at that time.
Another concern
sometimes voiced in fear of leaving a historic bridge standing next to its
replacement is that somehow the piers of the two bridges that might not line up
with each other could obstruct the flow of the water. However, take a look at
the historic Lynch Bridge and its ugly replacement. The historic bridge doesn't
have a single pier in the water, instead offering a single mighty span over the
creek, while the replacement bridge requires a pier to support its two short
spans. Think about it. The replacement bridge is inferior to the historic
bridge! The historic bridge spans the river in one span, which does not restrict
the flow of the water, while the replacement requires a pier in the creek, which
can obstruct the flow of water. Over a century of so-called technological
development, and engineers today are unable to efficiently and safely construct
spans as long as people a century ago could?! Fracture critical or not, having
served traffic faithfully for over a century, nobody can argue that the historic
bridge was an unsafe design.
The pier is placed because of modern engineer's desire super-redundancy.
Engineers fear what they call the "fracture critical" condition of truss
bridges, where in theory the failure of a single member of a truss bridge would
cause the collapse of the entire bridge, although in most cases the failure of
more than one member at the same time is required in reality, or a heavy load is
needed to cause collapse. This is because historic bridges were overbuilt in
many cases. Either way, modern engineers do not design complex bridges anymore,
and instead design simpler bridge types that have super-redundancy to them, such
as a concrete slab or multi-beam (stringer) bridge. These types of bridges are
inefficient, particularly the longer the span gets, and so a multi-span bridge
is usually required when that might not have been the case with historic truss
bridges, which are among the most efficient types of historic bridges ever
conceived in terms of material use.
Is this super-redundancy really needed in modern bridges? In many cases, this is the equivalent of wearing a helmet and bulletproof vest every time you walk out to get the mail. Do you really need that much protection? Perhaps you do, if you are careless and get the mail at 2:00 in the morning wearing diamond necklaces and a shirt made out of 100 dollar bills. Similarly, perhaps indeed you do also need a super-redundant bridge if you plan to ignore the inspection and maintenance of the bridge throughout its life. However, since neither are likely to occur, the extra safety is not needed. Just look at the Lynch Bridge. Despite a lot of deferred maintenance and neglect at the end of its life that resulted in considerable section loss at the lower connection points and flooring system, the Lynch Bridge safely carried traffic for over a century. All across the country, those "fracture critical" historic truss bridges that have been carefully maintained, preserved, and inspected over the years have proven that with proper care, fracture critical truss bridges are more than safe.
Engineers from the period of history in which truss bridges were common had a better understanding of these bridge types. They understood that while truss bridges did have a "fracture critical" risk of sorts, that in many cases, failure of one or more members of the truss did not cause the collapse of the bridge. Famous bridge engineer J. A. L. Waddell and his partner John Lyle Harrington not only understood this, they provided engineering explanation as to why this is the case. They even held the opinion that efforts to design more redundant truss types, such as the lattice truss, were not needed, since they understood that even a typical Pratt truss had enough strength in it to handle the failure of one or more truss members. This is detailed in The Principal Professional Papers of Dr. J. A. L. Waddell, Edited by John Lyle Harrington, dated 1905. The exact text from a discussion of railway bridges follows:
In regard to the styles and proportions of bridges, it is surprising what small changes time has wrought. The Pratt, the Petit, and the Warren trusses continue to be the general favorites. The use of the pony truss has been substantially discontinued, except in highway bridges, but the Warren truss with a double or triple system of cancellation has come into general use on a number of prominent railways. No economy is claimed for it, in fact, it is not quite so economical as the ordinary Pratt truss; but it is thought to be less liable to destruction in case of accident. Great publicity was given to an accident on the Chicago and Northwestern Railway, in which several web members of a double-intersection Warren-truss bridge were damaged or destroyed by a head-on collision without causing the failure of the bridge. It is true that similar accidents have occurred on Pratt truss bridges with equally satisfactory results, but they have not been given similar publicity, therefore a number of engineers are employing the multiple intersection Warren truss, chiefly because they have been led to consider it more safe. The riveted Pratt truss would appear to be quite as satisfactory in this respect, however, for in any truss, when the web member is destroyed, the shear must be carried by the chords in bending. Near the middle of the span where the shear is small and the chords are large, the unusual load should not ordinarily cause failure of the structure, especially if the accident be a head-on collision and the span be nearly uniformly loaded.
Finally, HistoricBridges.org does not feel that the executed mitigation for the demolition of this historic bridge (or any number of historic bridges replaced in Pennsylvania), as required by Section 106, are an appropriate form of mitigation. When a final decision is made that preservation of the historic bridge is not possible and the bridge must be demolished, then something must be done to mitigate the "adverse effect" caused by the demolition of the historic bridge. In all cases of replacement, PennDOT's strategy is to fulfill this mitigation by employing one, some, or all of a few minor changes to the design of its replacement bridge, including the use of concrete form liners to create a stone pattern on the piers and abutment, use of paint or weathering steel on the beams of the replacement bridge, and using steel two-tube guardrails instead of concrete New Jersey barriers. These changes to the modern bridge do nothing to help future visitors to the site interpret what type of historic resource was lost. Concrete form liners do not tell people that a metal truss bridge once stood there. Nor do any of these efforts preserve any of the original historic bridge's fabric.
HistoricBridges.org prefers the full preservation of every historic bridge in some manner. However, when that fight has been lost, it is still worth trying to work with agencies like PennDOT to help make sure that the mitigation is appropriate and is as effective as possible within a reasonable budget.
What should have been done here instead? Perhaps a portion of the historic truss could have been salvaged and placed near the site as a memorial, alongside interpretive signage describing the bridge. With the Lynch Bridge, salvage of anything from a single connection, salvage of portions of a vertical member and an eyebar, and/or salvage of a whole panel of the bridge would be useful alongside interpretive signage to explain the significance of the bridge, in particular the unusual construction of the diagonal members. This type of mitigation still will not fill the void left by the demolition of the historic bridge, but it would retain a portion of the original bridge material which is always important, and it would help future visitors to the area interpret what was once here.
HistoricBridges.org is willing and welcomes any opportunity to discuss and work with PennDOT to develop improvements to the way Section 106 mitigation is approached in Pennsylvania. Please contact us.
Information and Findings From Pennsylvania's Historic Bridge InventoryDiscussion of Bridge The pin connected, single span, 205'-long, Parker thru truss bridge was fabricated in 1905 and moved to its current location by the state highway department in 1948, replacing an earlier bridge at this location. It is supported on concrete abutments. The bridge has no innovative or distinctive details. It is a late and undistinguished example of its type and design. Pin connected Parker thru truss highway bridges dating from the late 1880s and the 1890s survive throughout the state. Earlier examples better represent the introduction and significance of the technology in northwestern Pennsylvania and in the state. Discussion of Surrounding Area The bridge carries a 2 lane road over a stream in a sparsely developed, forested setting near the village of Lynch. There is a T intersection with SR 666 at the northwest approach. The area does not have historic district potential. Bridge Considered Historic By Survey: No, But Later Re-Evaluated and Found Eligible. Information and Findings From Pennsylvania's Bridge Marketing WebsiteThe Lynch Village Bridge is a 205-foot long, 19-foot wide, pin-connected single-span Parker Through Truss bridge that carries the two-lane SR 1003 (Blue Jay Road) over Tionesta Creek. The ten-panel truss design features four vertical posts on either side of a king post, reinforced by diagonal ties that slope toward the center of the bridge The Eyre Construction Company, a Philadelphia concern, originally fabricated the bridge in 1905 on another site. In 1946, an earlier truss bridge on the site collapsed under the weight of a heavy delivery truck. Rather than construct an entirely new structure, township and county officials worked with the state highway department to relocate the well-built Parker Through Truss Bridge to the site in 1948. The Parker Through Truss became widely popular just prior to the turn of the century, due to its reputation as a durable design for single span bridges over 200 feet in length. PENNDOT and the Pennsylvania Historical and Museum Commission agree that the bridge is eligible for inclusion on the National Register of Historic Places for its technological significance. |
This historic bridge has been demolished. This map is shown for reference purposes only.
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