The bridge on highway I-35 that collapsed Wednesday over the Mississippi River was built 40 years ago and was under repair for minor problems.
MINNEAPOLIS, MINNESOTA: The bridge on highway I-35 that collapsed Wednesday over the Mississippi River was built 40 years ago and was under repair for minor problems, Minnesota state authorities said.
Constructed in 1967, the mainly steel structure stretches 581 meters (1,906 feet) across the river in Minneapolis and rests on 14 spans.
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The section of the bridge that straddles the Mississippi measures 300 meters (984 feet) and consists of three continuous spans, with the central part 139 meters (456 feet) long, and two others at 80 meters (262 feet) each.
In accordance with government regulations in force in 1961, the structure was designed using a cantilever method, with decks resting on triangular metal girders supported by arches between the spans.
Minnesota Governor Tim Pawlenty said that the bridge was last inspected in 2006 and no significant structural problems were found.
The governor said that engineers found the bridge deck would need attention in the future and that minor repairs were under way.
"They notified us from an engineering standpoint the deck may have to be rehabilitated or replaced in 2020 or beyond," he said.
There was work taking place on the bridge "relating to concrete repair and rehabilitation and replacement, guard rail replacement, righting replacement and work on the joints," he said.
But a 2001 report by the state's Department of Transportation pointed to problems with corrosion in the bridge's steel beams and "poor welding" in trusses.
The report also said that the design of the bridge, in which only two main trusses support the load of eight lanes of traffic, was "theoretically" at risk of collapse in the case of a single crack in a truss section.
The construction method used for the bridge was reevaluated in the 1970s and design regulations have since become stricter, according to the report.
For Minnesota's harsh winters, the bridge is equipped with an automatic system that sprays antifreeze on car lanes.
Interstate 35 is one of many national highways that criss-cross the United States. The north-south route stretches from the Canadian border to Laredo, Texas, at the border with Mexico, passing through Minneapolis, Kansas City, Oklahoma City and Dallas.
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