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The Fort Snelling Road bridge was a joint venture between the federal government and Ramsey County of Minnesota. Minnesota had passed laws in 1876, 1878, and 1879 pertaining to a bridge at this site. The 1878 law stated, “That said bridge shall be constructed so as to offer reasonable and proper means for the passage of vessels under the same, and width at least one hundred (100) feet between piers therefor.”
On March 29, 1878, the county voted $100,000 to build the bridge, and the Congress in the same year approved “The Sundry Civil appropriation bill … (which) contained an item appropriating $65,000 for aiding the construction of a free wagon bridge at the military reservation at Fort Snelling.” This amount “being one-half of the cost as estimated by the U. S. Engineers.” The Bill stated, “the height of said bridge shall be at least 68 feet above high-water mark, and that a span of at least 200 feet in the clear be provided from the right or Fort Snelling bank of said river toward the left bank thereof.” On April 4, 1878, Joseph S. Sewall, then an engineer in St. Paul, was chosen to make surveys by a committee appointed to oversee the design and construction, and on the 14th of the same month he was elected engineer of the work.” Sewall completed the plans and specifications for a cantilever bridge and sent them “to the Sec’y of War for approval, and by him referred to a commission composed of Gen’l Alfred H. Terry and G. K. Warren, by whom they were approved.” In 1878 Warren had prepared a report entitled “Bridging the Mississippi River between St. Paul and St. Louis” for the Chief of Engineers, U. S. It covered the 16 bridges that were in existence up to 1876.
The river valley at the site “had a width of about 800 feet, with steep rocky bluffs 80 to 90 feet in height, on each side. The low water channel is only about one-half this distance in width.” Steamboat traffic, while not as heavy as farther downstream, was still to be guaranteed free passage at all times.
Sewall prepared a specification on July 5, 1878, that was becoming standard practice and requested designs and bids for an iron bridge at this site in August 1878. The specifications stated that river traffic would have to be maintained and that the “superstructure be so proportioned and constructed that with a load of 1,800 pounds per lineal foot upon any part of the structure, there should be no tensile strain upon any part of the structure exceeding 12,000 lbs. per square inch, and no compressive strain exceeding one-fourth the breaking load of the part as calculated by Gordon’s formula.” The specification also prescribed the design be based upon a wind pressure of 50 lbs. per square foot … and iron in tension to have an elastic limit exceeding 25,000 lbs. per square inch. Bids were be submitted by September 30, 1878.
A remarkable 31 bids based upon the designs of the different bridge companies were submitted. The bids ranged from $39,444 to $69,000 but Sewall selected the design of Horace E. Horton & Company of Rochester, Minnesota, who had designed an unusual bridge consisting of five short truss spans on iron towers and a cantilever span with two, trusses serving as anchor spans. His bid, which was accepted on September 30, 1878, was for $44,328. Masonry bids had been received in August and the contract awarded to Michael O’Brien of St. Paul for $63,397. It was finished on June 19, 1879. Horton was to eventually receive $63,397 for the superstructure. The bridge would have an 18-foot-wide roadway and a five-foot wide sidewalk.
Engineering News reported on the bids in its January 4, 1879, issue noting, “There were 17 bidders, and 31 plans offered … The engineer, J. S. Sewall recommended that the bid of H. H. E. Horton & Co. of St. Paul, Minn., on their "Plan C" be accepted and the proper steps taken to secure the approval of the Secretary of War. The following are the companies that submitted bids, with several having options. The italicized firms have previously built spans across the Mississippi.
H. A. Streeter, Globe Iron Works, Chicago
Delaware Bridge Co., New York
Morrison, Field & Co., Buffalo, N. Y.
C. Shaler Smith, St. Louis
Cunningham & Keepers, Milwaukee
L. Soulerin, Chicago
Wrought-Iron Bridge Co., Canton, O.H.
Phoenixville Bridge Works, Pennsylvania
Detroit Bridge & Iron Works
Louisville Bridge & Iron Co. (Ky.)
Passaic Rolling Mill Co.. New York
New York Bridge Co.
F. E. Cauda, Chicago
H. E. Horton & Co., St. Paul
Keystone Bridge Co.. Pittsburgh, Pa.
Clinton Bridge Co., Iowa
American Bridge Co., Chicago
Horton’s Plan C involved one of the first cantilever spans in the United States. James Eads had used cantilever methods in erecting arches for his St. Louis Bridge in 1874 and C. Shaler Smith had erected his Kentucky High Bridge using cantilever methods in 1876. This bridge was built as a continuous three span bridge, but after erection the top chord was cut resulting in the end spans being supported by a brackets off the middle span that served as the anchor span. Smith would later build a cantilever over the Mississippi at St. Paul, Minnesota, in 1780 to be described in a future article. Horton was the first to build what became a true cantilever and the first to have the suspended span lifted into place and pinned to cantilever arms. It is not known what the other bridge companies had submitted. Horton’s bid of $44,325.00 was not the lowest. In fact, five reputable firms had under bid him. Despite this Sewall and Allen probably chose Horton based upon his proposed erection technique.
As can be seen in Figure 1, Sewall and Horton started on the Fort Snelling side (the south or west side) of the river and built a masonry anchorage pier with the end truss tied down to the anchorage. They would then build on falsework the first 135-foot anchor span. A one panel bracket was cantilevered off the anchor span and over the first main stone pier. Starting from the St. Paul side of the river, they had five simple trusses of 72.5-foot span resting on four iron towers of 18 feet width. The next span, built on falsework as well, and setting on stone piers, served as an anchor span for another one panel long bracket. This span was 180 feet long, discounting the bracket. The suspended span was slightly over 200 feet in length. The total length of the bridge was 1,020 feet. Since the trusses was designed for much lighter loads (carriage and foot traffic) its weight was not great and Horton decided to fabricate the suspended span off site, float it to the site on barges and lift it into place from the barge. This span had top chords of riveted channels and eye bar bottom chords and diagonals. It, like all the long span trusses, had intermediate posts (verticals) to support the deck at shorter intervals. No record is known to exist of the lift and the equipment used in the lift.
Captain Charles J. ALLEN was assigned to oversee the work, and he wrote:
“The contractors for the superstructure made their own bargains with the Keystone Bridge Company, of Pittsburgh, Pa., for the iron. Considering it as necessary to have the shop tests superintended by some person in whose report’s confidence could be placed, I informed the Board of Bridge Commissioners that such should be provided for. They requested me to nominate a person, to be paid by themselves. Colonel Merrill, to whom I applied, kindly named Mr. Charles Davis. He was accordingly employed by the Board of Bridge Commissioners … The contract between Horton & Co. and the Bridge Commissioners provided for the superstructure to be finished by September 1, 1879, and requiring a forfeiture of $25 per day for each and every day after that date that the completion of the superstructure was delayed."
Allen further wrote, “I required a test live load to be placed upon the bridge of 1,500 pounds per linear foot. Ice was found to be the most convenient material with which to load the bridge … It was agreed between the bridge engineer (Mr. Sewall) and myself that the deflection should not exceed the 1/1000 part of the length of span. The Fort Snelling Bridge passed its load test successfully and Ramsey County and the residents of St. Paul could now cross the Mississippi on a new, and somewhat novel, bridge.” The total cost for the bridge was $134,925 and opened March 15, 1880, or just short of a year after the contract for the superstructure was awarded.
Allen concluded his report with, “The bridge is probably the strongest wagon bridge in this vicinity, although without merit as to architectural effect. It will withstand all, but such extraordinary gales or hurricanes as defy engineering skill, and which occasionally visit the Mississippi Valley. The final test was a severe one.”
A St. Paul newspaper closed its article on the opening of the bridge with, “It is for this and future generations to profit by a pioneer project realized in solid stone and tenacious iron—graceful but strong, beautiful but durable.” Another newspaper wrote, “St. Paul can boast of a bridge, which in beauty, strength and durability, is unsurpassed by any other which spans the rolling waters of the Mississippi, from the Falls of St. Anthony to the Jetties, excepting the massive structure at St. Louis.”
The bridge was replaced in 1909 by a double steel arch bridge to accommodate heavier loads. It in turn was replaced in 1961 by a continuous steel girder bridge. ■
About the Author
Dr. Frank Griggs, Dist.M. ASCE, specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer (fgriggsjr@verizon.net).