Designers overestimated load capacity of critical FIU pedestrian bridge section: NTSB update report

0
826
ntsb image
(Samples of rebar recovered from the collapsed FIU pedestrian bridge, await transport to the Federal Highway Administration’s Turner-Fairbanks Highway Research Center, where the samples underwent materials testing as part of the NTSB’s ongoing investigation of the March 15, 2018, fatal, bridge collapse. NTSB photo by Adrienne Lamm)

The National Transportation Safety Board (NTSB) says in an investigative update about the fatal Florida International University (FIU) pedestrian bridge collapse in Miami that errors were made in the design of the 174-foot span, and that cracking observed before the collapse is consistent with those errors.

Six people died and eight others were injured when the bridge collapsed March 15, 2018. Eight vehicles were crushed in the collapse, seven of the vehicles were occupied, the NTSB says in its mid-November update.

Two days before the collapse, an engineer with the design firm, FIGG Bridge Group, left a voicemail for Florida Department of Transportation (DOT) officials to report cracking had been found at one end of the concrete span, but the company did not think it was an issue, the Associated Press reported.

State officials did not hear the voicemail until after the collapse. University officials said DOT officials had been included in a meeting to discuss the cracking hours before the collapse.

Representatives for the university, the design firm and Munilla Construction Management did not immediately respond to AP requests for comment.

The NTSB update states errors made were in the design of the northernmost nodal region of the span where two truss members were connected to the bridge deck. The design errors resulted in an overestimation of the capacity (resistance) of a critical section through the node, and, an apparent underestimation of the demand (load) on that section. The design review was conducted by the Federal Highway Administration’s Office of Bridges and Structures in support of the NTSB’s ongoing investigation. The Federal Highway Administration is a party to the NTSB’s investigation.

The Turner-Fairbanks Highway Research Center, part of the Federal Highway Administration, conducted numerous tests and examinations of concrete and steel samples taken from the bridge following its collapse. The concrete and steel specimens tested by Turner-Fairbanks Highway Research Center personnel met the project’s build plans specified minimum requirements.

Findings from the materials tests include:

  • Concrete core specimens from the bridge deck and bridge canopy met the compression requirements in the project plans;
  • The design plans specified concrete used for the project had to be in accordance with Florida Department of Transportation specifications. All specimens from the bridge deck and bridge canopy were within the specified range for total air content; and
  • Tension test results of size #5, #8 and #11 steel reinforcing bars revealed all met minimum yield and tensile strengths and percent elongation at fracture, for their respective sizes. Size #7 bars could not be tested due to collapse-induced deformation.

The NTSB’s investigation of the bridge collapse is ongoing and the information contained in the investigative update is preliminary and will be supplemented or corrected as the investigation progresses. As such, no conclusions about probable cause should be drawn from the information contained in the investigative update, the agency says.

The investigative update is available online at https://go.usa.gov/xPGnG.

Share this:

LEAVE A REPLY

Please enter your comment!
Please enter your name here

3 × one =

This site uses Akismet to reduce spam. Learn how your comment data is processed.