failure
SYSTEM FAILURE CASE STUDIES
SEPTEMBER 2009 VOLUME 3 ISSUE 06
A Half-Inch to Failure
At 6:05 pm, on Wednesday, August 1, 2007, the Interstate-35
West (I-35W) bridge over the Mississippi River in
Minneapolis collapsed. On the day of the collapse, four of the bridge’s eight lanes were closed for planned construction. Four weak connector plates fractured under the combined burden of rush hour traffic, concentrated construction equipment, and previous heavy renovations.
The bridge fell 108 feet into the Mississippi River. The police, fire department, and U.S. Coast Guard immediately initiated rescue operations. Of the 190 people on or near the bridge, thirteen died and 145 were injured.
BACKGROUND he I-35W bridge supported a 1,907 foot long, 8-lane wide roadway that served Minneapolis for forty years. The state inspected the bridge annually using the National Bridge Inspection Standards set by the Federal
Highway Administration (FHWA). Inspectors had been labeling the bridge “structurally deficient” since 1991. This label indicated that the bridge required significant maintenance and repair to remain in service, but not that it was unsafe (inspectors would have closed the bridge if they believed it was unsafe). A structurally deficient rating is not uncommon; approximately 12% of U.S. bridges are rated structurally deficient.
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Steel truss bridges, like I-35W, were more frequently labeled structurally deficient; approximately 31% of the 465 steel truss bridges in the U.S. were listed as structurally deficient at the time of the collapse. Such bridges consist of straight beams of steel formed into triangular units (Figure 1). In large steel truss bridges, the ends of the beams are connected with riveted metal plates called gusset plates. I-35W’s gusset plates connected three beams at each node: two diagonal beams and one vertical beam (Figure 2).
Over the course of forty years, the state of Minnesota conducted significant
SEPTEMBER 2009 VOLUME 3 ISSUE 06
A Half-Inch to Failure
At 6:05 pm, on Wednesday, August 1, 2007, the Interstate-35
West (I-35W) bridge over the Mississippi River in
Minneapolis collapsed. On the day of the collapse, four of the bridge’s eight lanes were closed for planned construction. Four weak connector plates fractured under the combined burden of rush hour traffic, concentrated construction equipment, and previous heavy renovations.
The bridge fell 108 feet into the Mississippi River. The police, fire department, and U.S. Coast Guard immediately initiated rescue operations. Of the 190 people on or near the bridge, thirteen died and 145 were injured.
BACKGROUND he I-35W bridge supported a 1,907 foot long, 8-lane wide roadway that served Minneapolis for forty years. The state inspected the bridge annually using the National Bridge Inspection Standards set by the Federal
Highway Administration (FHWA). Inspectors had been labeling the bridge “structurally deficient” since 1991. This label indicated that the bridge required significant maintenance and repair to remain in service, but not that it was unsafe (inspectors would have closed the bridge if they believed it was unsafe). A structurally deficient rating is not uncommon; approximately 12% of U.S. bridges are rated structurally deficient.
T
Steel truss bridges, like I-35W, were more frequently labeled structurally deficient; approximately 31% of the 465 steel truss bridges in the U.S. were listed as structurally deficient at the time of the collapse. Such bridges consist of straight beams of steel formed into triangular units (Figure 1). In large steel truss bridges, the ends of the beams are connected with riveted metal plates called gusset plates. I-35W’s gusset plates connected three beams at each node: two diagonal beams and one vertical beam (Figure 2).
Over the course of forty years, the state of Minnesota conducted significant