Seventh Street Improvement Arches
Encyclopedia
The Seventh Street Improvement Arches are a double-arched
masonry highway bridge that formerly spanned the St. Paul and Duluth Railroad
tracks in St. Paul, Minnesota. 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 in 1883-1884 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
.
Construction on the bridge began in September 1883, with Michael O'Brien of St. Paul doing general contracting for excavation, foundation, and abutments. McArthur Brothers of Chicago was responsible for the final construction of the bridge, which opened for traffic on December 18, 1884. Truesdell's engineering colleagues recognized his achievements, even if the general public soon forgot the significance of the bridge. The Association of Engineering Societies Journal characterized the bridge as "the most important piece of masonry in the city" upon his death in 1909.
The railroad tracks have since been removed, but the bridge still stands. Today, the Bruce Vento Regional Trail
follows the former railroad line under the bridge.
Arch bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...
masonry highway bridge that formerly spanned the St. Paul and Duluth Railroad
St. Paul and Duluth Railroad
The St. Paul and Duluth Railroad was reorganized from the Lake Superior and Mississippi Railroad in 1877. It was bought by the Northern Pacific in 1900...
tracks in St. Paul, Minnesota. 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
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
. It was built in 1883-1884 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
National Register of Historic Places
The National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...
in 1989 and on the American Society of Civil Engineers
American Society of Civil Engineers
The American Society of Civil Engineers is a professional body founded in 1852 to represent members of the civil engineering profession worldwide. It is the oldest national engineering society in the United States. ASCE's vision is to have engineers positioned as global leaders who strive toward...
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
Northern Pacific Railway
The Northern Pacific Railway was a railway that operated in the west along the Canadian border of the United States. Construction began in 1870 and the main line opened all the way from the Great Lakes to the Pacific when former president Ulysses S. Grant drove in the final "golden spike" in...
, 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
Skew arch
A skew arch is a method of construction that enables an arch bridge to span an obstacle at some angle other than a right angle. This results in the faces of the arch not being perpendicular to its abutments and its plan view being a parallelogram, rather than the rectangle that is the plan view of...
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
Peter Nicholson (architect)
Peter Nicholson was a Scottish architect, mathematician and engineer. Largely self-taught, he was apprenticed to a cabinet-maker but soon abandoned his trade in favour of teaching and writing...
in 1828. This method was mathematically rigorous, but since Truesdell studied mathematics as a hobby, he decided to accept the challenge. The voussoir
Voussoir
A voussoir is a wedge-shaped element, typically a stone, used in building an arch or vault.Although each unit in an arch or vault is a voussoir, two units are of distinct functional importance: the keystone and the springer. The keystone is the center stone or masonry unit at the apex of an arch. A...
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
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
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
Kasota, Minnesota
Kasota is a city in Le Sueur County, Minnesota, United States. The population was 675 at the 2010 census.-Geography:According to the United States Census Bureau, the city has a total area of , all of it land....
.
Construction on the bridge began in September 1883, with Michael O'Brien of St. Paul doing general contracting for excavation, foundation, and abutments. McArthur Brothers of Chicago was responsible for the final construction of the bridge, which opened for traffic on December 18, 1884. Truesdell's engineering colleagues recognized his achievements, even if the general public soon forgot the significance of the bridge. The Association of Engineering Societies Journal characterized the bridge as "the most important piece of masonry in the city" upon his death in 1909.
The railroad tracks have since been removed, but the bridge still stands. Today, the Bruce Vento Regional Trail
Bruce Vento Regional Trail
The Bruce Vento Regional Trail is a rail trail in the cities of Vadnais Heights, Gem Lake, Maplewood, and Saint Paul, Minnesota, USA.The trail occupies an abandoned Burlington Northern Railroad corridor and intersects with the Gateway State Trail in Maplewood and continues to just east of Lake...
follows the former railroad line under the bridge.