Errors made in design of doomed FIU pedestrian bridge, NTSB report states

Report: Errors made in northernmost nodal region of bridge

By Amanda Batchelor - Senior Digital Editor

MIAMI-DADE COUNTY, Fla. - Errors were made in the design of a 174-foot bridge connecting Florida International University to the city of Sweetwater that collapsed earlier this year, killing six people, a second investigative report from the National Transportation Safety Board stated.

According to Thursday's report, cracking in the FIU pedestrian bridge, which was photographed, is consistent with the design errors.

Authorities said six people were killed and eight were injured when the bridge collapsed March 15. Eight vehicles were crushed by the bridge, seven of which were occupied.

According to the NTSB report, the design errors were of the northernmost nodal region of the bridge, where two truss members were connected to the bridge deck.

"These design errors resulted in (1) overestimation of the capacity (resistance) of a critical section through the node comprised of diagonal member 11 and vertical member 12; and (2) apparent underestimation of the demand (load) on that same critical section," the report stated. "Additionally, the FHWA evaluation determined that the cracking observed in the node prior to the collapse is consistent with the identified errors."

The NTSB reported that the design review was conducted by the Federal Highway Administration's Office of Bridges and Structures, which is a party to its investigation.  

The Turner-Fairbanks Highway Research Center, which is part of the Federal Highway Administration, conducted multiple tests and examinations of concrete and steel samples taken from the pedestrian bridge following the collapse. 

Below is a list of findings from the Turner-Fairbanks Highway Research Center:

  • Test results showed that all the concrete core specimens obtained from both the bridge deck and the canopy met the compression requirements per the project plans.
  • The design plans specified that the concrete used for the project was required to meet Florida Department of Transportation specifications. All specimens from both the bridge deck and the canopy were within the specified range for total air content.
  • Two types of specimens were tested during evaluation of the post-tensioning rods: machined round bar specimens and full-size bar specimens. For all tension tests, the specimens met the specified minimum yield strength, tensile strength and percent elongation at fracture.  
  • The steel reinforcing bars collected from the collapsed structure included several different sizes, identified as #5, #7, #8, and #11. Collapse-induced deformation of the size #7 bars precluded their testing. Tension test results for the remaining size #5, #8, and #11 bars found that all met the minimum yield strength, tensile strength and percent elongation at fracture for their respective sizes.

 According to the report, the materials tested by the research center met the minimum requirements specified in the project's build plans. 

 

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