Motorists on Sweetwater, Florida’s Southwest Eighth Street found themselves in the middle of the scene of tragedy last Thursday, March 15. Florida International University (FIU) was in the process of constructing an overpass to connect their campus when the 174 foot concrete structure came tumbling down on top of seven lanes of traffic. Up to eight cars were trapped underneath and six lives were taken.
Crews removed 950 pounds of debris in search of victims. The names of those who perished were just released, including Alberto Arias, Navaro Brown, Brandon Brownfield, Alexa Duran, Rolando Fraga and Oswaldo Gonzalez. The students at FIU held a vigil on Wednesday to remember the victims, some of whom were students at the university.
The president of FIU spoke about the impact of the collapse and the grief that has consumed the community. “There is much uncertainty, but there are a few things for certain,” Mark Rosenberg said. “This is a strong community, this is a caring community – a community that will comfort one another through this.”
He assured those in attendance that the lives of the victims will not be forgotten. “This is a community that rises time and again, and the other certainty is that we are going to carry the memory of the victims,” Rosenberg continued. “We will carry that memory forever.”
The construction of the bridge was set to finish in 2019, after it had been pre-assembled as to not disrupt the seven lanes of traffic beneath it. The day of the collapse, the top of the bridge was being worked on to address some cracking in the concrete. The cracking is not unusual when building with concrete and is not necessarily a cause for alarm.
While the official cause has yet to be determined in light of the ongoing investigation, it is thought one of the diagonal support trusses at the end of the bridge failed, causing it to collapse. FIU’s pedestrian bridge is known as a truss bridge, a design that is typically avoided. These types of bridges have a risky vulnerability: if a single truss is hit or damaged, there is no additional reinforcement to prevent the entire bridge from collapsing. It was reported that there was structural damage to the bridge as it was put in that may have contributed to the collapse.
FIU chose this design, despite its known vulnerabilities, due to the strictly pedestrian nature of the bridge itself. This bridge had several qualities that were cause for alarm apart from the design. The trusses that hold up the bridge are typically found on both sides of the bridge, but FIU’s had trusses on one side only with a mast on the top for purely aesthetic reasons. The bridge also used concrete instead of steel. The concrete, while heavier, is cheaper and is more durable.
Despite crew’s efforts to repair the damage and reinforce the structure, many engineers have pointed out that there are reasons truss bridges are avoided: their vulnerability makes this an undesirable design. While there are many theories about the cause of the collapse, the investigation is ongoing.
