Photo courtesy PRNewsfoto/FIU
The National Transportation Safety Board (NTSB) that is investigating the March 2018 pedestrian bridge collapse in Miami said in a preliminary report errors were made in the design of the 53-m (174-ft) span. Cracking observed prior to the collapse of the structure at Florida International University (FIU) is consistent with those mistakes.
Six people died and eight others were injured when the bridge collapsed in March 15, 2018. Eight vehicles were crushed in the collapse, and seven of them were occupied.
According to the NTSB update, 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 Turner-Fairbanks Highway Research Center (TFHRC), part of the Federal Highway Administration (FHWA), conducted tests and examinations of concrete and steel samples taken from the bridge following its collapse. The specimens tested by TFHRC 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 the Florida Department of Transportation (FDOT) 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.
My gut feeling has always been a shear failure (concrete) morphing into a bond failure (concrete to steel) as the shear failure load path engaged the embedded steel intimate with the shear failure zone. I suspect there is very little ruptured steel associated with this collapse in the immediate vicinity of the failure origin.
I suggest reviewing the computer assumed structural model of the bridge. Many of the current structural engineers depend on the output of computer software without clearly understanding the exact behavior of the intended structure and without properly modeling the structure. It should be noted that the computer software provides the output based on the input “Garbage in, Garbage out”.
I agree with your comment, there is too much reliance on computer software and copy paste work without fundamental know-how
The upper part and lower part of the bridge is nothing more then flat concrete. Non-Beam design ( Flat ). Then you stick X type braces between 2 pieces of flat concrete. Those braces are to small. And are nothing more then pinch points to cause those cracks. 170 feet. The lowers and uppers should of been I Beam design. But if not. Then the I Beam should’ve been incorporated between the 2 sandwich pieces. 10 foot of connecting concrete then 10 foot space. 10 more of the connecting concrete and so forth…. That would’ve made a legitimate Beam of the whole structure… But. I would still stuck some brace at the half way point. From the ground up anything..Would’ve been 100% improvement for safety for decades. Truth be told