Interstate 35W bridge over the Mississippi River collapsed this past August during rush hour traffic. The 40-year-old deck steel truss structure had indicated structure deficiencies in 2001 showing poor fatigue details on the main truss and floor truss system.
The bridge is composed of three parts: a deck made of concrete and rebar, superstructure made of steel, and substructure made of steel and concrete footing. Construction crews reported that the bridge began to wobble as they removed a portion of the bridge deck as part of a resurfacing project. Authorities, including the National Transportation Safety Board and the American Society of Civil Engineers, are focusing on the southern end of the span, which “behaved differently” as it fell in order to identify the cause of the accident.