Historic Bridges

Details

County supervisor's records do not mention this modest concrete arch structure, belying its significance to the bridge building industry. Why the county decided to use an innovative structural type for a rural crossing in which a pony truss could have been built for less money remains unknown, but for some reason Lyon County elected to build one of America's first reinforced concrete arch bridges. The structure traces its roots to Austria in the early 1890s, where an engineer named Josef Melan was developing a new system of concrete reinforcement. Melan's design employed parallel steel beams embedded in the concrete to provide the tensile strength that concrete inherently lacked. He used an elliptical arch profile for his bridge, with the steel placed at the arch's intrados. Melan's system was introduced to the US by another Austrian, Fritz von Emperger, who obtained a patent for it in 1893.

That year von Emperger designed his first Melan arch bridge-a small-scale structure over Dry Creek south of Rock Rapids, in Lyon County, Iowa. The structure featured a 30-foot span, 16-foot roadway, and a six-foot rise of the elliptical arch. The bridge's spandrels were faced with Sioux Falls jasper. The reinforcing consisted of five 4-inch beams embedded in a concrete rib that thinned to six inches at the crown. Rock Rapids builder John Olsen was hired to build the bridge, and cement was shipped to the site from Germany at a cost of $3.25 per barrel and mixed with sand and crushed jasper. Completed in 1893 at a cost of $830, the bridge carried traffic in unaltered condition until the early 1960s, when increased traffic prompted the county to plan its replacement. Responding to overwhelming local sentiment, the county and the state highway commission moved the concrete structure to a park in Rock Rapids in 1964, where it has stood to the present.

"Melan's system, introduced in America in 1893, was used extensively in highway bridges and in some pedestrian spans," stated David Plowden in Bridges: The Spans of North America. "It can be said to have heralded a new and unimaginative era of bridge design." This bridge in Lyon County was, to be sure, a modest step in bridge evolution. With its 30-foot span, it could almost as well have been built using unreinforced concrete, and it was faced with stone to give the appearance of a stone arch. But the step was a significant one, for it marked one of the first attempts at reinforced concrete bridge construction in America. The Rock Rapids bridge is Melan's most important work-a nationally significant introduction to Iowa and the country [adapted from Fraser 1992].