Investigators continue to look for the cause of a pedestrian bridge collapse at Florida International University on March 15.

The 950-ton bridge segment, which was under construction, fell onto a busy highway, killing six people. The 174-foot-long segment had been lifted into place on March 10.

News reports say that at the time of the collapse, engineering crews were conducting stress tests on the incomplete $9.3 million structure. That stress testing typically involves placing weights on the span and measuring how the structure responds to ensure it’s within safe parameters. Crews may also have been adjusting tension cables that provide structural strength for the span’s concrete slabs.

Image of the collapsed bridge after it failed March 15.(Learn more about the field of forensic engineering.)

News reports caution that testing or tension adjustments may not have caused the structure to fail. Other factors that still need to be investigated may also come into play.

Reports also said that engineers had reported cracks in concrete on one side of the bridge two days before the collapse. Cracks are not uncommon in concrete and may not have been related to the accident.

(Search standards at IEEE Engineering360 related to bridge construction.)

The National Transportation Safety Board launched a "Go Team" to investigate the bridge collapse. It released a poster showing engineering drawings of the bridge.

The pedestrian overpass was being built using a relatively novel approach called accelerated bridge construction. Coincidentally, in 2016 Florida International University was awarded $1.5 million per year, for five years, by the U.S. Department of Transportation for its Accelerated Bridge Construction University Transportation Center.

It was the second grant awarded to the program, which was first funded by USDOT in 2013. The university program was intended to work closely with the Federal Highway Administration and the American Association of State Highway and Transportation Officials to advance accelerated bridge design and construction, through research, workforce development and technology transfer.

(Click to enlarge.) Workers lift the bridge segment into place on March 10. Credit: Miami Herald via KLRNThe bridge structures' concrete deck was to be post-tensioned with straight tendons and the truss members and the canopy were to be compressed with high strength cables and bars. The 109-foot-tall concrete pylon had not yet been installed at the time of the collapse. Reports say the bridge was to be self-supporting without the pylon and associated stays.

According to information from the University, the bridge that collapsed was being built by MCM Construction and was designed by FIGG Engineering-Bridge Group. It was assembled nearby and was moved into place on March 10 by Barnhart Crane & Rigging, which provided and operated self-propelled modular transporters.

Funding for the bridge came from the U.S. Department of Transportation TIGER Grant, the Florida Department of Transportation, Florida International University and the City of Sweetwater, Florida.

The university also awarded a contract through a competitive process to Bolton Perez and Associates to provide construction, engineering and inspection services.

The bridge was expected to be completed in early 2019.