|Bridge Name||Facility Carried / Feature Intersected||Location||Structure Type||Construction Date and Builder/Engineer|
||Park Trail Over Park Grounds||Decorah: Winneshiek County, Iowa||Metal 12 Panel Pin-Connected Bowstring Through Truss, Fixed||1878 By Builder/Contractor: Wrought Iron Bridge Company of Canton, Ohio|
|Main Span Length||Structure Length||Roadway Width||Main Spans|
|159.6 Feet (48.6 Meters)||160 Feet (48.8 Meters)||16 Feet (4.8 Meters)||1|
This bridge is the second longest bowstring truss span in the United States, along with the Little Church Road Bridge, and in addition the bridge retains near-perfect historic integrity with no major alterations to the bridge superstructure noted. As such, it is nationally significant as one of the most important bowstring truss bridges in the country. Iowa has the richest collection of historic bowstring truss bridges in the country, and among the surviving examples in the state (all of which are extremely important), this bridge stands out because of its size and integrity.
The bridge 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. Some verticals are latticed, while other verticals are made of built-up star-members (cruciform members). There are cast iron connection assemblies on the bridge, including a seven point intersection assembly for the truss web. This intersection assembly, as well as the floorbeam caps are cast iron and include a decorative star design. Original fishtail style floorbeams remain on the bridge. Unusual etch marks on edges of the metal on the keystone column top chord at rivet points appear to have been some sort of measurement aid, the exact purpose of which is unknown.
This bridge has been relocated from its original location and sits in a park setting as an exhibit The bridge may be walked on, but the bridge does not cross anything. The bridge has not been altered in any manner as part of this relocation and preservation, which is good because it maintains the high level of historic integrity that this bridge enjoys.
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
Crossing the Upper Iowa River near Decorah, the
Freeport Bridge was constructed in 1879 and measures 156 feet in length.
It is one of four bowstring arch bridges in Winneshiek County, and is
the second longest existing in the country. The Wrought Iron Bridge
Company of Canton, Ohio built the bridge.
Bridge Considered Historic By Survey: Yes
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