This is an unusual bridge. The following is the best available history following research of online reports by Bruce County.
Hugh Watt and Thomas French Pearse constructed a bridge at this location in 1920, consisting of two concrete slab spans at the southern end, and a truss (of unknown design type) at the north end. This original truss was reportedly incorporated into the 1920 design plans late in the process, a decision made to better accommodate high flood waters. At a later date (one source states 1930) this truss span was apparently destroyed (perhaps by the aforementioned floods) and replaced with an unusual lattice truss span. The lattice truss span was reportedly a former railway span that was reconfigured for highway use.
This bridge's signature truss span is nearly identical to the bridge seen on Concession Road 8, and the two truss spans may share a common history, since the Dudgeon Bridge's truss span is a relocated span. Both spans may have come from the same original bridge, in an unknown location. Despite the similarities of these two bridges, both bridges are unique among the thousands of bridges in Canada and the United States on HistoricBridges.org. These two bridges may be the only examples of their kind in North America. Quadruple Warren truss bridges in North America generally are found as through or deck truss bridges, not pony truss bridges. The bridges, with their lattice pony truss configuration and unusual vertical end posts, are strongly reminiscent of a European style of bridge known as a lattice girder bridge. Europe's lattice girder bridges generally will have lighter and more numerous diagonal members forming a very tight lattice, but the overall visual appearance is strikingly similar. European lattice girder bridges are often pony truss bridges.
The field visit to this bridge by HistoricBridges.org showed that its design and appearance is nearly identical to the aforementioned Concession Road 8 Bridge. The mystery remains as to where these trusses came from originally. The theory that they were originally railway spans seems logical. Their heavy trusses are typical of railway design, and more often than not, riveted lattice truss bridges are railway bridges rather than highway bridges. However, pony truss bridges of any kind are rare on railroads. Trusses are generally deck trusses or through trusses. However, this bridge shows no evidence of rivet holes on the top chord that might indicate that it was originally a deck truss. In fact, there was no major evidence that the trusses were altered. Signs of alteration to be expected might include empty rivet holes, areas where metal was cut with a torch. The presence of modern welds or bolts are another thing to look for as a sign of more recent alterations. However, that is the challenge with this truss. It was relocated when riveting was still in its prime, and so its possible that the bridge was altered, but because the same type of fasteners were used, rivets, it is not easy to distinguish alterations on the bridge like it would be an alteration from the 1980s where bolts and welds would have been used.
The bridge has relatively shallow, closely spaced floor beams which rest on the bottom chord. Railway bridges typically have fewer, and far deeper floor beams. It is likely that the floor beams are replacements and may be wider than the original floor beams since railway bridges, if single track, are very narrow. The original floor beams, particularly if this really was a railway bridge, were likely deeper beams and likely built-up rather than rolled.
The two concrete approach spans at the southern end of this bridge date to 1920. There are shallow arched fascias that appear to be more decorative than structural in nature that give these spans an arch-like appearance. It appears that the spans actually function as concrete slabs.
Given the apparent rarity of this truss both in Canada and the United States, this bridge (and its companion on Concession Road 8) should be considered among the rarest, and most historically significant truss bridges in Canada. Their rural location and heavy-duty trusses, especially if rehabilitated, should be sufficient for the areas they serve.
Bruce County had discussed replacing this bridge, but it appears for now that the bridge is safe from demolition. Instead, some repairs were made to the approach span railings. The deck on the bridge appears to be fairly new as well.
The design of this bridge as a truss in general has a very unusual and noteworthy feature. With the truss diagonal members being composed of angle and plate, these are riveted directly to the top chords and bottom chords to form a connection. There are none of the gusset plates that are typical for a bridge with rigid connections, whether riveted, bolted, or welded. Gusset plates provide an interface with which to join members together. Additionally, the floor beams for the bridge rest on top of the bottom chord, which eliminates the need for any gusset plate type connections between the floor beams and bottom chord.
Gusset plates have gotten a bad (and unfair) reputation which began when a gusset plate that had been improperly designed (yet functioned for decades) suddenly failed on the I-35W bridge in Minneapolis, MN in 2007, causing the entire truss bridge to collapse. Gusset plates have performed safely and reliably on numerous bridges that are over 100 years old, the only reason this bridge collapsed was because it was not designed properly. Any improperly designed bridge could collapse, whether it uses gusset plates or not. Regardless, this event led to engineers developing a dislike of gusset plates. As a result, when a historic truss bridge called the Memorial Bridge was replaced in Portsmouth, New Hampshire, a new truss that eliminated gusset plates was designed. The method was different than that of the Dudgeon Bridge's trusses. The Dudgeon Bridge eliminates gusset plates by directly riveting the truss members to the chords, which was made possible thanks to large chords and small, simple diagonal members. With the new Memorial Bridge, the connection of diagonal members to chords is pre-fabricated and uniform, and the actual truss members are bolted together in a splice, some distance away from the actual connection point. Regardless of the method, the facts are clear. Both the Dudgeon Bridge and the new Memorial Bridge eliminated the use of gusset plates in their design. Despite this fact, the engineers who designed the new Memorial Bridge have proudly proclaimed that their bridge, built in 2014, is the first truss bridge in the world to eliminate the use of gusset plates. This is taking credit where credit is not due. For here in rural Bruce County, a truss bridge without gusset plates (that may well be over a century old) has been serving traffic safely and reliably for decades! It is sad that today's bridge engineers not only lack experience in the preservation and rehabilitation of heritage truss bridges like this one, but they don't even have knowledge of the history of bridge design.
The following text is taken from a variety of documents produced for Bruce County as they have been developing county transportation plans and evaluations of the future of its bridges.
Located between the Municipalities of Brockton and Arran-Elderslie, Dudgeon Bridge carries Greenock-Brant Road across the Teeswater River. The Dudgeon Bridge is located south of the Gregg Bridge. The Dudgeon Bridge contains two distinct structure types. The earlier, two span, concrete structure was constructed across the Teeswater River flood plain. It appears to be either a concrete beam or concrete slab structure, although this was not field verified. It is clear in the original design plans that the second span was added late in the design phase in order to accommodate high flood waters. The concrete portion was constructed by Hugh Watt and Thomas French Pearse in 1920. A steel truss with a latticework design spans the waterway. The superstructure sits on the original south concrete abutment and the second pier of the concrete structure. The 1920 design plans show the presence of a truss structure different from the current structure. Although a later addition, it is likely that the steel structure was constructed in the 19th century as the latticework design was a common railway bridge design in the 1880s. Repurposed for use on a roadway rather than railway, it replaced the original structure at an unknown date. The roadway curves slightly at the bridge, likely due to the challenging topography surrounding the two branches of the Teeswater River. As a result, when approaching from the south, the bridge is completely hidden from view. From the north side, the roadway veers to the east so that the bridge crosses the Teeswater River so as to minimize the skew of the bridge.
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