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National Transportation Safety Board Investigation


NTSB Releases Third Investigation Update

The NTSB has issued a third update on the collapse of the I-35 W bridge. The update includes statements extracted from NTSB Chairman Rosenker's testimony to the  U.S. House of Representatives' Transportation and Infrastructure Committee hearing on Sept. 5 on structurally deficient bridges in the U.S. 

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NTSB Releases Second Investigation Update

On Aug. 22, the National Transportation Safety Board (NTSB) issued a second update on their investigation of the I-35 W bridge collapse.  A new facet of the investigation is the examination of the de-icing system that was installed on the bridge and the properties of the chemical used in this system, specifically whether or not it is corrosive. This de-icing system had components installed in the concrete bridge deck. The NTSB Chairman Mark Rosenker stated: "The finite element model of the bridge is being revised based on the measured deck thickness from core sections and physical examination of the bridge structure. All structural elements have been incorporated in the model; however, some aspects of stiffness, weight and connections between elements are being modified to match the condition of the bridge the day of the accident." The NTSB has also interviewed 25 drivers and construction workers who were involved with the construction project on the bridge at the time of its collapse.  According to the NTSB press release: "The weights of the various construction materials that were delivered to the work site between 11:00 a.m. and 2:30 p.m. on Aug. 1 have been verified at about 383,000 pounds. The combined weight of the loads and construction vehicles is about 575,000 pounds."  NTSB has verified the location of these vehicles and materials by means of the interviews and from a pre-collapse photograph taken by a passenger on an airplane that was departing from Minneapolis on the afternoon of the collapse.

To read the full press release from the NTSB, click here.


NTSB Investigation Update

The National Transportation Safety Board (NTSB) has issued an update on their investigation of the I-35 W Bridge. The NTSB is working with engineers from the Federal Highway Administration's (FHWA) Turner Fairbank Highway Research Center in McLean, Va. to conduct a detailed structural analysis of the bridge. The NTSB indiciated that it is reviewing construction records to determine the location of construction equipment and raw materials on the bridge at the time of the collapse, and to verify the weights of those vehicles and materials. The chairman of the NTSB team stated: "NTSB investigators have observed a design issue with gusset plates at particular locations (gusset plates are steel plates that tie steel beams together)." Safety Board investigators are in the process of verifying the loads and stresses on the gusset plates at these locations, as well as the materials used in constructing the gusset plates. NTSB investigators in helicopters at the site also observed several tensile fractures "but nothing that looked to be the initiating location." 

To read the full NTSB update, click here. 


Investigation into the I-35W Collapse

The National Transportation Safety Board (NTSB) has announced the investigation into the collapse of the highway bridge in Minneapolis, Minnesota. NTSB Chairman Mark V. Rosenker conducted the briefing.

Click here to read the news release.



Investigations of Previous Collapses



The NTSB conducts investigations into bridge collapses. Reports and recommendations related to previous collapses are available on the NTSB Web site.

Click here to view and read these reports.