Parkville Waddell "A" Truss

View the Historic American Engineering Record collection for this bridge

Located in the town of Parkville, this extremely unique bridge is one of two examples of this design known to exist in the United States. This unique bridge was originally constructed in 1898 for the Quincy, Omaha & Kansas City Railroad (QO&KC); a small railroad company which constructed a line between West Quincy, Missouri and Kansas City between 1897 and 1899. This bridge was originally located across Linn Branch, northeast of Trimble, Missouri; located in rural Clinton County. The first configuration of the bridge, built in 1898, consisted of a 100-foot Waddell "A" truss, set onto steel caisson piers and approached by timber trestle spans on either side. A&P Roberts Company/Pencoyd Iron Works would fabricate the truss. The truss was one of a number of such spans designed by John Alexander Low Waddell, a prolific Canadian-American bridge engineer. Similar to all "A" trusses, the span utilizes pinned connections, heavy members and four panels, each 25 feet in length. The QO&KC became part of the much larger Chicago, Burlington & Quincy Railroad system in the late 1910s.

Because the QO&KC was constructed mainly to serve rural agricultural industries, the railroad had little importance to the CB&Q. In addition, because the railroad was late to the railroad development in Missouri; the line did not serve any major population centers, except for Kansas City. As a result, much of the QO&KC in western Missouri was abandoned in 1939. After sitting abandoned for 14 years, the bridge was rehabilitated and converted to Missouri Route D in 1953. During the rehabilitation for roadway use, the original deck was removed and a new wooden deck installed; and steel beam spans replaced the original timber trestle approaches.

During the late 1970s, work on the Smithville Reservoir threatened this bridge; and the bridge was removed from the original location in 1980. The bridge was then disassembled and stored at the Army Corps of Engineers facility near the dam, awaiting future reuse. By the mid-1980s, Parkville desired to construct a new pedestrian bridge in English Landing Park to cross Rush Creek. It was decided that the bridge would be reused at this location, and volunteers carefully reassembled the bridge, placing it onto new concrete abutments. The bridge reopened to pedestrian traffic in November 1987, thanks to the dedication of the community and of volunteers.

The "A" truss was a unique design, developed in 1892 by Waddell. During the late 1880s and early 1890s, Waddell had become frustrated with the lack of a suitable span to bridge the gap between plate girders and larger through trusses. During his time in Japan in the late 1880s, Waddell noted that many of the bridges were designed by British engineers, and utilized short span lengths and riveted connections. Waddell often dismissed the use of pony trusses for railroad spans, as the lack of a top lateral bracing made the spans susceptible to vibrations under loading. Waddell also disapproved of the use of riveted connections, as he felt they could not be installed properly in the field. Waddell would later write in his book De Pontibus:
"For a number of years the author was dissatisfied with all railroad bridges for spans between the superior limit of the plate-girder and a length of about one hundred and fifty feet, ordinary pin-connected, through, Pratt trusses being too light and vibratory, and the riveted bridges as then built being clumsy, unscientific, and uneconomical. On this account he tried for some time to find an opportunity to experiment upon a design of his own to fill a portion of the gap, but the opportunity did not occur until April 1893, when he was retained by the General Manager of the Kansas City, Pittsburg, and Gulf Railroad Company to design some bridges. After a little persuasion, the General Manager was induced to agree to build a 100-ft. "A" truss span as an experiment; but when he saw the completed plans he ordered at once four bridges to be built therefrom, and this style of structure was soon afterwards adopted as the standard 100-ft. span for the road.
These bridges have shown such rigidity under traffic that they have been used on the St. Louis Southwestern Railway, and have been adopted as the standard for spans between sixty-five and one hundred and sixteen feet- by the Nippon Railway Company of Japan. The advantages of this type of bridge are great rigidity in all directions, ease and cheapness of erection, and economy of metal when it is compared with structures of other types having equal strength and rigidity."

The design of the "A" truss was inspired by A-frame roof trusses, typical in buildings throughout the world. These trusses utilized a triangular shape, an extremely unusual feature for truss bridges, particularly spans designed for railroad use. This design provided a breakthrough to solve the issues Waddell found with bridge design at the time, as the height of the truss allowed a lateral bracing to be installed, and the 25-foot standard panel lengths allowed standardization of fabrication and easier construction. This design would quickly fall out of favor with railroads in the United States as Pratt designs were refined and riveted trusses became popular. Waddell would continue his career into the 20th Century, becoming one of the most iconic bridge designers of the time.

The true number of these spans constructed is unknown. In 1916, Waddell again wrote about the design in his 1916 book Bridge Engineering:
"The "A" truss bridge, patented many years ago by the author, served a good purpose for sometime until the modern Pratt truss bridge was evolved. Quite a few of them were built, and nearly all are still in use, notwithstanding the fact that some are frequently overloaded as much as sixty (60) percent. It is the most rigid short-span, pin-connected bridge ever built. Its appearance is odd but not displeasing."

As of 2024, only two of these spans are known to still exist, with the other located at Shreveport, Louisiana. It is currently unknown if other spans of this design were constructed for the QO&KC, or if there may be other "A" trusses hidden throughout the United States. Many of these spans were likely scrapped in the 20th Century, as railroads sought to upgrade mainline bridges to meet heavier loading demands. A number of "A" trusses may have been reused on branch lines and spurs during this time, as was the case with the Shreveport bridge. Because of the unique and extremely rare design, the author has ranked this bridge as being nationally significant. It is hoped that this bridge can be preserved and cherished for generations to come.