The Hennepin Avenue Bridge, or the Steel Arch Bridge, was a dual-span hinged arch bridge crossing the Mississippi River at Hennepin Avenue from the west bank of Minneapolis to Nicollet Island. It replaced a 1876 suspension bridge, which in turn replaced an 1855 suspension bridge which had been the first span to cross the Mississippi. The northernmost span was built in 1888 and the southern span was built in 1891. After receiving renovations in 1897, 1931, and 1954, the bridge's northern and southern spans were demolished and replaced in 1988 and 1989, respectively, as they were replaced by the current Hennepin Avenue Bridge.
The bridge, a century-old at its demolition, consisted of two spans steel arch spans. The bridge had special historic significance to engineering as the two spans were built by different companies in different styles.[2] While both spans are hinged arch bridges, the northern span was built with a two-hinge design, and the later southern span was built as a three-hinge design after the northern span was found to "jiggle" under the load of traffic. This dual-design nature of the bridge later contributed to it being considered historic. The corrugated steel deck gave a tenor hum as vehicles drove across.[3]
History
Background
The population of Minneapolis greatly expanded from 47,000 in 1880 to 185,000 in 1890. By 1884, it had become clear that the 1876 suspension bridge was no longer sufficient.[4]:2Hennepin County authorized funding for an 80-foot-wide stone arch bridge.[5][4]:3 However, there was opposition to this proposal; by milling companies because of the three piers that would be required and a possible reduction in power output from the river, and also from others who wanted to preserve the "beautiful" previous bridge.[6][4]:3–4 Despite the opposition, construction began in December 1885 but an injunction was obtained by a milling company to halt work in January 1886.[7][6][4]:4 A reevaluation by engineers recommended a steel arch bridge with a single pier. As an added benefit, this structure would also be cheaper.[4]:4 The dual steel arch bridge was designed by Andrew Rinker, the Minneapolis city engineer, and Frederick William Cappelen.[1]
Construction
The bridge's northern span was built by the Keystone Bridge Company of Pittsburgh, and the $187,613 ($6.36million in 2023) span became open for travel on June 3, 1888. For some time, the new steel arch bridge and the old suspension bridge stood side-by-side.[4]:5 The new steel arch span and the previous suspension bridge stood side-by-side until it became clear the suspension bridge was no longer structurally sound.[4]:5–6 At that time, bids were accepted for a second, southern span. The second span was built by Wrought Iron Bridge Company of Canton, Ohio, and was substantially completed by January 1891.[4]:7 The total cost of the bridges was $266,365 ($9.03million in 2023).[3] Each span consisted of two 280-ft arches. The roadway was 56 feet wide, with 12 feet for sidewalks.[1]
The bridge received three major renovations over the course of its life. The first was in 1897, installing buckle plates and repaving the northern half of the bridge.[4]:18–19 In 1931, the brick paving was replaced by timber overlaid with asphalt.[1][4]:19 A 1954 renovation removed the timber deck and replaced it with an open mesh steel I-beam deck, and at the same time added concrete curbing, new guard rails, and new lamp posts.[8][9][4]:19
By 1982, Hennepin County had begun looking into replacing the at the time 94-year-old bridge. Without major renovations or replacement the county estimated the bridge would only last another five years. with over 20,000 vehicle crossings every day, the bridge was showing an inability to keep up with the load of modern traffic.[2] While in good condition, the aging bridge was determined to need around $10 million ($24.6million in 2023) in remodeling costs. However, county officials required that the bridge be able to carry six lanes of traffic with the potential to accommodate light rail lines, which scuttled plans to renovate rather than rebuild the bridge.[10]
The year 1987 saw Congress pass the Surface Transportation and Uniform Relocation Assistance Act, which required states to inventory historic bridges and attempt to rehabilitate or relocate qualifying bridges before demolition.[11] Following a call from a government bureaucrat informing him of the requirement, Ted Hoffman, the chief design engineer of Hennepin County, advertised the bridge as for sale in January 1988. Hoffman expressed incredulity at the concept, stating that he couldn't "imagine someone going to that expense".[3] By July the bridge began to be gradually disassembled, one hundred years after its completion.[12][a] The northern half was torn down in 1988, and the southern half in 1989 after the northern half of the new bridge opened.[1]
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