“The Seventh Street Improvement Arches of St. Paul, Minnesota A Study of Their History and Oblique Method of Construction”

Abstract

Complex masonry structures, constructed through hard work and intense dedication, offer some of the greatest representations of how man has risen to the challenges found in the structures that he has aspired to build. A special case within these structures is the oblique bridge, which solves the problem of when two overlapping paths meet in a non-perpendicular manner. Though this historic type of structure was more commonly built in Europe than within the United States, there exists a rare case within the city of St. Paul, Minnesota – the Seventh Street Improvement Arches – which not only took on this structural feat, but also earned a place in the National Register of Historic Places in 1989. This study analyzes the construction of this historic bridge to determine the oblique-arch method that was implemented for its construction from 1883 to 1884. Research is primarily based upon the original 1883 drawings of the structure found at the City of St. Paul’s Bridge Division Office, as well as the corresponding writings from the project’s engineer – William A. Truesdell (1846-1909) – discovered in the fifth volume of the Journal of the Association of Engineering Societies (1886). These two sources, along with visits to the State Historic Preservation office and meetings with local historians, work to reveal the adoption of helicoidal, or spiral, stone pieces that involved the intricate carving and shaping of the arch’s construction. Further analysis is accomplished by taking various measurements and firsthand documentation of the structure, as well as through the construction of a three-dimensional computer model using PhotoModeler. The synthesis of the findings – based upon the past and present sources – serves as evidence of the complexity involved with this structure, and the masterful use of masonry, which is one of oldest construction traditions that humankind has worked with.