I-35 Bridge in Miinneapolis, Minnesota Collapsed and Sent 80 Souls to Their Death

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The I-35W Bridge, located in Minneapolis, Minnesota, was a bridge that opened in November of 1967 and was designed by Sverdrup & Parcel and Associates, Inc. The bridge had a truss arch design that spanned a total distance across the Mississippi River of 1907 feet. Also, the bridge was a deck truss which means the roadway was located on top of the truss itself. With a total of 4 piers, 2 on either side of the Mississippi River, that supported the bridge, the I-35W Bridge crossed the Mississippi River in 3 main spans; the longest span, which was located directly above the river, was 458 feet long. On August 1, 2007, the I-35W Bridge collapsed and sent the 80+ vehicles on the bridge into the Mississippi River.
The reason for the collapse was
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In other sections of the bridge, gusset plates got as thick as 1 3/8”. A thicker plate should have been used on joints like the U10 joint. The designer of the bridge made an error in the design analysis when calculating the thickness of each gusset plate needed for each joint.
The design error along with a few other factors led to the collapse of the bridge. When the bridge first opened, the traffic deck had 2 lanes of traffic going in each direction for a total of 4 lanes. However, in 1998, the bridge was renovated so that there were 4 lanes of traffic going in each direction for a total of 8 lanes. Along with a few other bridge renovations, the weight of the bridge was significantly increased. Also, the rush hour traffic and the construction vehicles located on the bridge for repairs during the day of collapse added a considerable amount of weight too.
Under these circumstances, the center span of the bridge collapsed and fell into the Mississippi River. All four gusset plates at the U10 nodes fractured since they were inadequate in strength for the demand being exerted on to them. When these first gusset plates fractured, other gusset plates started to fracture and break too because the design of the bridge was non-load-path-redundant. In other words, if one piece, such as the U10 gusset plate, failed, then the whole bridge would fail too. The U10 gusset plate fracture led to a sequence of events that sent the I-35 Bridge down into the Mississippi

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