Seventh Street Improvement Arches
About this property
The Seventh Street Improvement Arches are a double-arched masonry highway bridge that formerly spanned the St. Paul and Duluth Railroad tracks in Saint Paul, Minnesota, United States. The Seventh Street Improvement Arches are historically significant for its rarity and the technically demanding nature of its skewed, helicoidal spiral, stone-arch design. The bridge is one of the few of its type in the United States, and is the only known bridge of its type in Minnesota. It was built from 1883 to 1884 by Michael O'Brien and McArthur Brothers of Chicago and was designed by William A. Truesdell. The bridge was listed on the National Register of Historic Places in 1989 and on the American Society of Civil Engineers Historic Civil Engineering Landmarks in 2000. The bridge was proposed in 1883 as part of a group of improvements along Seventh Street, linking downtown St. Paul with the Dayton's Bluff neighborhood on the east. Other parts of this project included a 300-foot iron bridge crossing the Northern Pacific Railway, a long embankment, and a stone-arch sewer for the crossing of Phalen Creek. These improvements were necessary because the hill on Seventh Street needed to be rebuilt to lessen its steepness, so streetcars could travel between downtown and the Dayton's Bluff neighborhood. The Seventh Street Improvement Arches bridge posed a special engineering challenge because the street crossed the St. Paul and Duluth tracks at a 63-degree angle. The bridge also had to carry sewer and water pipes and match the rest of the profile of the regraded hill, making a substantial amount of fill necessary. This precluded the construction of a bridge with ribbed arches, because this method could not support all the weight of the fill. Truesdell also considered using the classical French method of skewed arch construction, but the amount of skilled stonecutting necessary would have made the cost prohibitive. He turned to the helicoidal or spiral method, introduced by British architect Peter Nicholson in 1828. This method was mathematically rigorous, but since Truesdell studied mathematics as a hobby, he decided to accept the challenge. The voussoir stones were cut with curved surfaces to form a series of parallel spiral courses. The initial calculation of the curves was difficult, but once the calculation was performed, all of the voussoirs (except for the ring stones) could be cut from the same pattern. This required the stonecutters to work with more precision than they were used to, but a skilled foreman helped to organize the work. The abutments, piers, and wing walls were built with a variety of gray limestone locally quarried in St. Paul, while the voussoirs, ring stones, coping and spandrel walls were built with a buff-colored limestone quarried in Kasota, Minnesota.
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Property data from the National Register of Historic Places, National Park Service (public domain).
Description adapted from Wikipedia under the Creative Commons Attribution-ShareAlike 4.0 International License.
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Questions about this property
When was Seventh Street Improvement Arches listed on the National Register?
Seventh Street Improvement Arches was listed on the National Register of Historic Places on November 6, 1989.
What type of historic resource is Seventh Street Improvement Arches?
Seventh Street Improvement Arches is classified as a structure in the National Register of Historic Places.
What is the period of significance for Seventh Street Improvement Arches?
The period of significance for Seventh Street Improvement Arches is recorded as the industrial era.
Can I research the history near Seventh Street Improvement Arches?
Yes. Aubrey Research reports search National Register listings, battlefield records, land patents, and other primary historical sources within any radius of a US address. A report for an address near Seventh Street Improvement Arches will include this listing and all other historical records in the area.
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