The partially constructed pedestrian bridge over an eight-lane road in Miami experienced a structural failure on 15 March. As a result, the 53m-long bridge fell about 5.6m onto the road. Eight vehicles below the bridge at the time of the collapse were fully or partially crushed; seven of the vehicles were occupied. One bridge worker and five vehicle occupants died; four bridge workers and four other people were injured.
The NTSB began its investigation immediately after the collapse (link opens in new tab).
It is evaluating the bridge design, the construction process, and the construction materials. In addition, the NTSB is evaluating the emergence of cracks in the region of diagonal members 2 (south end of the bridge) and 11 (north end of bridge) and the propagation of cracks in the region of diagonal member 11.
Photo by Bolton-Perez & Associates Consulting Engineers
Photographic documentation from 24 February shows cracks in the region of diagonal member 11.
Photo by Bolton-Perez & Associates Consulting Engineers
The bridge was to be completed by early 2019 and was built using an accelerated bridge construction method, with the intention of minimising disruption of traffic. On 10 March, the walkway, diagonals and canopy comprising the bridge had been moved from the construction lot into position across the roadway and then lowered onto the piers.
In accordance with the bridge design plans, construction crew members de-tensioned the bridge diagonal members on the north and south ends of the bridge. When the collapse occurred on 15 March, a construction crew was positioned on the structure working on re-tensioning the number 11 diagonal member connecting the canopy and the deck at the north end of the bridge. A crane was being used for this work and so two of the three westbound lanes below the north end of the bridge were closed to traffic; however, the five eastbound lanes remained open, and eastbound traffic was not detoured.
In the next month, the NTSB will be conducting additional forensic examination of several bridge structural components and destructive testing of multiple core and steel samples. All aspects of the collapse remain under investigation while the NTSB determines the probable cause, with the intent of issuing safety recommendations to prevent similar events.
