As searchers combed the river for victims, federal officials looking into the cause of the collapse issued an advisory for states to inspect the metal plates, or gussets, that hold girders together on bridges nationwide.

Investigators said gus-sets on the failed Minnea-polis bridge were original-ly attached with rivets -- old technology more likely to slip than bolts used in bridges today.

15 January 2008
Yes, Gusset plates were the culprit!

(Read also the Follow-up below!)

Federal agency traces Minnesota bridge collapse to design flaw.

The Washington Post (1/15, A3, Wilber, Laris) reports, "A design flaw caused a Minnesota bridge to collapse last summer, killing 13 people and injuring 100 in an accident that focused renewed attention on the safety of the nation's highways and bridges," federal sources familiar with the investigation said. On Tuesday, the National Transportation Safety Board (NTSB) "is expected to announce...that investigators have traced the failure to steel structures known as gusset plates that held together beams on the Minneapolis bridge." The "plates are a common feature on steel bridges across the nation. ... They hold together angled beams on the bridge's frame." According to the sources, "the fault in the Minneapolis span stemmed from the bridge's design and would not have been discovered during detailed state inspections." Notably, "When the bridge was constructed in the 1960s, its gusset plates were not thick or strong enough to meet safety margins of the era, the sources said. Over decades, renovations added weight to the span."

        USA Today (1/15, Levin) adds that the NTSB "plans to call Tuesday for states to perform safety assessments on...gusset plates in steel girder bridges any time they add weight to a bridge." According to sources, "In the wreckage of the I-35W bridge, investigators found 16 gusset plates that were fractured. ... Eight of the plates were in the location on the south side of the bridge where the collapse began." Fracture discoveries "prompted engineers to calculate whether the plates were adequate to hold the bridge together." They concluded "that the half-inch thick plates should have been an inch thick -- double the size."

[Above Right: Photo taken from side opposite from above left photo.] The eight-lane  I-35W highway bridge in Minneapolis, Minnesota, USA, collapsed under rush- hour traffic at 6:05 p.m. CT Wednesday [Aug. 1, 2007] sending more than 50 cars plunging 20m into the Mississippi River. 4 people were killed and dozens more injured, and with many cars submerged in the Mississippi River, death toll is expected to rise.
[Material sourced from internet, msnbc, bloom-berg, etc. ... used here only for educational and informative purposes - NK]

Now for the gusset plates ... They are simply plates which enable all truss members meeting at a joint to be connected so that they may act together.
[Pictures below of Easton Turnpike (County Route 614) over the North Branch of the Raritan River]

FOLLOW-UP!
18 March 2008 :: More on the collapse

The New York Times (3/18, A17, Wald) reports, "The Interstate 35W bridge over the Mississippi in Minneapolis collapsed last August after construction workers had put 99 tons of sand on the roadway directly over two of the bridge's weakest points," a new report from the National Transportation Safety Board (NTSB) revealed. A diagram released Monday by the NTSB listed every object, and its weight, on the bridge at the time of collapse. It put "four mounds of sand, each 12 feet wide and stretching about 55 feet, in a lane between the four operating traffic lanes." According to a report released earlier by the Federal Highway Administration, "Stress at one of the two weakest points was 83 percent more than it could have handled." NTSB "researchers calculated a [total] load of 1.26 million pounds, or 630 tons, including 198,820 pounds of sand at the critical spots. However, the load would not have been excessive for a well-designed bridge, according to experts."

        Minnesota's Pioneer Press (3/18, Hoppin) explains that as "part of an ongoing road resurfacing project, fine and coarse aggregate were placed on a short stretch of roadway cordoned off from traffic,...directly above where the NTSB found a design flaw" that led to the collapse which killed 13 and injured 145 people. Furthermore, "close to 100 additional tons of cement mixers, water trucks and other construction equipment was located near the piles of aggregate." In January, "the NTSB said it was focusing on a design flaw in the bridge: a handful of massive gusset plates -- the steel plates that hold the truss bridge's steel beams together -- were one-half-inch thick and insufficiently designed." The Press notes that the NTSB found "that several inches of concrete had been added to the bridge's roadway over the years, adding to the weight on the bridge."