Following the collapse of the pedestrian bridge in the Florida International University onto a busy highway on 15 March, forensic engineers are investigating how it happened.
The 950-ton partially assembled bridge collapsed onto stationary vehicles, killing six people and seriously injuring nine others. It was being built by using the acceleration construction method and had only been moved into place five days earlier.
The National Transport Safety Board (NTSB) has revealed workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge in Miami collapsed. The investigation team has ordered the removal of components for further examination and testing. These include sections of the floor, canopy, a vertical member and a diagonal member, from the north end of the bridge where cracks were reported prior to the event.
President of the National Academy of Forensic Engineers in the US, Martin Gordon, said investigators will study video, design plans and the accelerated bridge construction method for clues. The professor of manufacturing and mechanical engineering technology, while not involved in this investigation, has been a forensic engineer for almost 20 years. He said collecting evidence does not begin until survivors are rescued and victims are recovered.
“Those operations displace material and can damage evidence, which means forensic engineers must study the emergency response as well, to be able to tell whether, for instance, a support column collapsed during the event or was destroyed to reach a victim,” Professor Gordon wrote in The Conversation US.
Forensic engineers will also review drawings and plans, he explained, and examine industry standards and site engineers’ calculations to understand what was supposed to be built, compared with what was actually constructed.
“They’ll look at photographs and videos of the collapse to identify the sequence of events and locations of key problems,” Prof Gordon stated.
“[And] they’ll also talk to witnesses to find out what workers and passers-by saw and heard around the time of its collapse.”
The tall centre pylon and pipe supports were not yet in place when the bridge collapsed and were not scheduled to be added until later, according to Prof Gordon. The investigation would look into whether this plan was a reasonable expectation, he explained, and if the missing elements reduced the strength of the span.
Image source: AP/Wilfredo Lee via The Conversation US.