But what caused the bridge to
fail? The Miami Herald has published
an extensive investigative report,
starting with these questions:
“Did it crack when it was lifted
into place? Was it a snapping steel
support that did it in? Or was it a fa-
tally flawed design from the start?
And what was the doomed construc-
tion crew member doing when the
bridge buckled under him?”
Each of these questions could
have different answers, and the
newspaper reported about specula-
tions and varying interpretations
within engineering forums. But the
details of what really happened are
4 – SPRING 2018 — Florida Construction News
stored at the NTSB and it may take a
year or more for the investigators to
release their findings.
In the most recent news release
March 21, the federal agency said:
“The next update on the progress of
this investigation will likely be the
preliminary report. Preliminary re-
ports are generally completed within
a few weeks following completion of
field work. Preliminary reports do not
contain analysis and do not address
probable cause.”
In other words, NTSB will likely be
totally silent for several weeks, and
then will decline to answer (at least
for now) the questions about why
the tragedy occurred.
In its March public statement, the
NTSB said that significant develop-
ments in the investigation include:
• Investigators secured a contract
to have a company remove com-
ponents from the bridge that it be-
lieves warrant additional
examination and testing. These
components include sections of
the floor, the canopy, a vertical
member and a diagonal member;
all from the north end of the struc-
ture. These components were in
the area of where the failure oc-
curred. “In addition to these com-
ponents, we obtained additional
core samples from this area to
supplement the core samples we
obtained earlier,” the NTSB state-
ment said.
• Shipping the core samples along
with some recovered rebar and
tensioning rods to the Turner Fair-
bank Highway Research Center, in
McLean, VA, for testing and evalu-
ation. • The investigative team has ob-
tained an exemplar tensioning rod
and hydraulic unit used by the
construction crew to make ten-
sion adjustments to the tension-
ing rods. These items are also
being shipped to the Virginia re-
search center for evaluation and
testing. • The larger bridge components the
investigative team is removing are
being stored at a secured Florida
Department of Transportation fa-
cility, under the control of the
NTSB. The additional examina-
tions and forensic deconstruction
of these components will occur
there. • The investigative team has con-
firmed that workers were adjust-
ing tension on the two tensioning
rods located in the diagonal mem-
ber at the north end of the span
when the bridge collapsed. They
had done this same work earlier at
the south end, moved to the north
side, and had adjusted one rod.
They were working on the second
rod when the span failed and col-
lapsed. The roadway was not
closed while this work was being
performed. NTSB says ongoing work includes:
• Removal of the post-tensioning
device to a temporary storage
area and preparing it for ship-
ment; • Preliminary comparison of bridge
schematics to measurements ob-
tained during the investigators’ ex-
amination of the collapsed
structure; and
• Interviews with first responders.
The NTSB said that “while seg-
ments of the bridge are being trans-
ported to and stored at an FDOT
facility, there are no plans to recon-
struct the bridge as part of the NTSB
investigation into why the bridge col-
lapsed. The nature of the structure
and the way it failed make recon-
struction impractical.”
There have been unofficial specu-
lations about whether the design
was properly evaluated before con-
struction began, and whether the
contractor had received briefings on
how to safely build the structure.
“Outside expert speculation has
moved beyond just potential con-
struction error to focus increasingly
on possible design flaws that might
have made the bridge structurally
vulnerable,” the Miami Herald re-
ported. “I would say they were pushing
the envelope,” Nel Hawkins, an
emeritus engineering professor at
the University of Illinois who special-
izes in concrete construction was
quoted as saying. “The question is,
to what extent had the new concepts
in this been validated through testing
prior to actually putting it in place?”
The Herald reported that the “ad-
mittedly speculative consensus has
coalesced around a view of the FIU
project as a novel design with a high
‘wow’ factor, but also hidden struc-
tural risks and vulnerabilities that
were probably compounded by a
last-minute design change, all
brought to a catastrophic conclusion
by engineering and construction mis-
calculations.” But it will likely be many months –
perhaps years – with presumably ex-
tensive litigation – before the story
can truly come to a definitive conclu-
sion. The story touches close to the
heart of FIU, with nationally recog-
nized programs in engineering and
construction management.
The university’s Moss School of
Construction, Infrastructure and Sus-
tainability attracts students from
across the U.S. and internationally
with its programs.
The school is “the preeminent
center for advancement and dissemi-
nation of construction knowledge,”
director Irtishad Ahmad says on the
FIU website. “Our undergraduate stu-
dents get hands on training and high
class instructions in all areas of con-
struction. Graduate students take
courses in advanced topics in con-
struction and get involved in re-
search with the faculty members.
Both groups enjoy excellent employ-
ment opportunities by being in South
Florida – one of the busiest geo-
graphic regions in construction in the
country.” Florida Construction News — SPRING 2018 – 5