This bridge was originally part of a two-span bowstring bridge that served Main Street in Independence, Iowa. One of the two spans was relocated to this site in 1891 to serve as the main span for a new Taylor's Ford Bridge.
They Taylor's Ford Bridge is significant as an early surviving example of a Wrought Iron Bridge Company bowstring that also retains excellent historic integrity with remarkably little alterations. In addition, the bridge is significant for its 1891 approach spans, because the supports for the three southern approach spans (the fourth approach span is at the north end) are iron bents that consist of built-up beams similar to those seen on pin-connected Pratt truss bridges. This form of substructure from this era is relatively uncommon to find remaining today on highway bridges. The main bowstring span sits on equally impressive and relatively tall caissons, which are also called lally columns.
The main bowstring truss span includes typical Wrought Iron Bridge Company bowstring details as outlined in the original patent. The top chord is a Keystone column. Sway and portal bracing are latticed. There are cast iron connection assemblies on the bridge. The Taylor's Ford Bridge has a different connection detail at the bridge shoe assembly at the ends of the bottom chord than a number of other Wrought Iron Bridge Company Bowstrings. Instead of the two large bolts that hold the bottom chord in place, the bottom chord is connected by a pin. In contrast, the bottom chord segments between the ends are riveted rather than pinned as seen on some bridges.
The Taylor's Ford Bridge has been bypassed and left in place for its historic value. This preservation solution is an easy and cost-effective one that enables vehicular traffic to travel Nolen Avenue without restriction, while also retaining an important historic resource. Also because the bridge no longer carries vehicular traffic, there is no need to alter the original design of the bridge to increase a weight limit. Despite the ease and value of this type of preservation solution, some states such as Pennsylvania refuse to even consider such forms of preservation, instead wasting money on the demolition of a historic bridge next to its replacement.
Bowstring truss bridges are sometimes called bowstring arch bridges because they have similarities to both structure types. Beginning with Squire Whipple's Whipple Arch Bridges, such as the Ehrmentraut Farm Bridge, the bowstring truss bridge is the bridge type that began a transition away from wood and stone and began to make metal a common bridge building material. It also began a period of experimentation until a good bridge form was developed, leading to a gradual standardization of bridge design. During this period, numerous bridge companies all experimented with metal, trying to design the best bridge. Each company had their own distinctive bowstring design, including unique and creative design details. These designs were often patented. Most bowstring truss bridges were built in the 1870s. Also during this time, cast iron was still used in addition to wrought iron for the construction of bridges, so many bowstrings built during this period include details such as connection assemblies that are made of cast iron. By the 1880s, bridge companies decided that the pin-connected Pratt truss was a better structure type, and construction of bowstring bridges sharply dropped after 1880. Because of the period in which Iowa was first being settled, a much larger number of bowstring truss bridges were built in the state than in other states. As a result, even today, Iowa has more historic bowstring truss bridges than any other state, although the number of bridges statewide is under 20, a very small number. However, a number of states do not have even a single historic bowstring truss within their borders. As such, while bowstring truss bridges are very few in number in Iowa, they are extremely rare on a national scale. It is imperative that each surviving bowstring in the county be preserved to protect this key period in bridge building history.
Historic American Engineering Record created a large and very informative historical overview and context for Iowa's bridges, and it is offered here by HistoricBridges.org in convenient PDF format for easy printing or offline viewing. The HAER source for the documents composing the PDF is here.
In its discussion about a single bowstring bridge, Historic American Engineering Record included a detailed description of the Wrought Iron Bridge Company and a general history and discussion of its bowstring truss bridges in general. HistoricBridges.org has clipped this section for convenient viewing in PDF format. The HAER source for the documents composing the PDF is here.View Bowstring Arch Bridges of Iowa, An Online Book By Michael Finn (PDF)
Michael Finn has composed a concise and detailed overview of Iowa's beautiful historic bowstring bridges. It has been made available for free by Iowa Department of Transportation.View Historic American Engineering Record's Structural Analysis of Iron Bowstring Bridges (PDF)
Historic American Engineering Record created a large and very informative structural analysis of how bowstring truss/arch bridges function. Everything from basic discussion of the engineering behind the bridges to advanced mathematical equations are available. The HAER source for the documents composing the PDF is here.
Information and Findings From Iowa's Historic Bridge Inventory
Discussion of Bridge
This long-span iron bridge crosses the Wapsipinicon
River in southeastern Buchanan County, four miles southeast of the
county seat, Independence. The structure was once part of a two-span
iron bowstring bridge, which carried Main Street over the Wapsipinicon
in Independence. A 1914 county history reported that the earliest
bridges in the county, including the Main Street Bridge, "were poorly
constructed, cheap affairs and every spring freshet damaged them to a
more or less extent, often the loss being entire. It was not until the
county began to build all-iron structures, in 1870, that this changed.
As it was building the Independence bowstring bridge, the Wrought Iron Bridge Company was under contract with the county to erect other iron bowstring trusses in Quasqueton and Fairbank. In its extensive dealings with the Wrought Iron Bridge Company in the 1870s, Buchanan County was simply following a regional trend: the bridge company was one of the largest bridge fabricators in America. In addition, its president, David Hammond, distinguished himself as one of the country's most prolific bridge innovators. Documentation shows that the primary superstructural type marketed by the WIBCo in the 1870s was the bowstring arch-truss made up of wrought and cast iron components. The bowstring was the most commonly erected all-metal bridge of the 1870s, owing in large part to WIBCo and its main competitor, the King Bridge and Manufacturing Company of Cleveland, Ohio. Both companies fabricated standardized versions of their own patented bowstring designs. The Taylor's Ford Bridge is thus both technologically significant because it is an early example of a once prevalent bridge design, the bowstring arch-truss, and it is historically notable since it was erected by one of the most prolific bridge builders in the Midwest during this decade, the Wrought Iron Bridge Company [adapted from Hybben, Roise, and Fraser 1992].
Bridge Considered Historic By Survey: Yes
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