Bridge Collapse Investigation Finds Many Problems

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NTSB’s FIU Bridge Collapse Investigation Finds Many
Problems
The agency published 30 ndings as part of its presentation on the bridge
collapse’s probable cause
The National Transportation Safety Board included numerous technical reports on the FIU bridge collapse, along
with a video summarizing the events leading up to the March 15, 2018, tragedy. (Image courtesy NTSB)
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October 23, 2019
Scott Judy and Tom
Ichniowski
During its three-hour-plus-long presentation on the cause of the Florida
International University pedestrian bridge collapse, ofcials with the National
Transportation Safety Board referred to its roughly 18-month-long
investigation as one of its most complex.
NTSB Chairman Robert Sumwalt noted that he’s been on the safety board for 13 years and deliberated over
nearly 200 accidents. He said, “I don’t think I’ve ever seen one where there’s more nger-pointing between
the parties. And you know, the nger-pointing is actually correct. Everybody’s pointing at everyone else.
In fact, that is correct—because everyone shares a piece of this accident. There were errors up and down
the line.”.
As part of its Oct. 22 presentation into the bridge collapse’s probable cause, the NTSB listed 30 ndings
from its investigation. The ndings are included as part of the NTSB’s abstract report, the full version of
which readers can nd here.
As the agency notes in its abstract, “The nal report and pertinent safety recommendation letters will be
distributed to recommendation recipients as soon as possible. The attached information is subject to
further review and editing to reect changes adopted during the Board meeting.”
Due to the list of ndings’ length, for our readers’ convenience—and to invite possible reader comment
and discussion—ENR is publishing all of these ndings here, in their entirety, without editing.
Findings
1. The emergency response by local re departments and law enforcement personnel was timely and
adequate.
2. The concrete and steel materials used during construction of the pedestrian bridge were not a factor in
its collapse.
3. The hydraulic jack used to post-tension the steel rods in member 11 was operating as expected at the
time of the bridge collapse.
4. (1) The FIGG Bridge Engineers (FIGG) bridge design was nonredundant because it provided only a
singular load path, (2) FIGG used poor judgment when it determined the bridge was a redundant structure,
and then, (3) FIGG erroneously used a redundancy factor of 1.0, which is commonly used for structures
with redundant load paths.
5. Even if the cold joint surface of nodal region 11/12 had been roughened to a 0.25-inch amplitude, node
11/12 would not have had sufcient capacity to counteract the demand load for interface shear—and the
bridge would still have been under-designed and could have failed.
6. The FIGG Bridge Engineers construction plans inconsistently identied when intentionally roughened
surfaces were needed to fulll the assumptions of the bridge design.
7. Because FIGG Bridge Engineers (1) did not use the lower bound load factor for determining the
governing net compression, Pc, in the interface shear; and (2) incorrectly increased and amplied the
effects of the clamping force across the interface shear surface, its bridge design calculations resulted in a
signicant overestimation of capacity.
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8. FIGG Bridge Engineers (1) made signicant design errors in the determination of loads, leading to a
severe underestimation of the demands placed on critical portions of the pedestrian bridge; and (2)
signicantly overestimated the capacity of the member 1/2 and 11/12 nodal regions.
9. Based on analytical modeling results, FIGG Bridge Engineers should have considered the loadings from
all critical construction stages when designing the pedestrian bridge and determining the governing
interface shear demands.
10. In several instances throughout the bridge design process, the FIGG Bridge Engineers models produced
reasonable estimations for interface shear demand, but these values were not always used in the design of
truss members to resist force demands.
11. FIGG Bridge Engineers’ analytical modeling for the bridge design resulted in a signicant
underestimation of demand at critical and highly loaded nodal regions.
12. The concrete distress initially observed in nodal region 11/12 is consistent with the underestimation of
interface shear demand and the overestimation of identied capacity in the bridge design.
13. The FIGG Bridge Engineers design of the rebar placement in node 11/12 resulted in less reinforcing
steel being available and diminished resistance to the critical interface shear demand, which contributed
to the collapse of the bridge.
14. The member 11/12 nodal region contained nonstructural voids (four hollow vertical pipe sleeves and
the horizontal drain pipe) within the concrete that made it less able to resist applied loads, which
contributed to the destabilization of this node through overstress and the subsequent collapse of the main
span.
15. Although it may be generally accepted that concrete itself is susceptible to cracking, the rate of
premature concrete distress was clear evidence that the structure was progressing toward failure and
should have alerted FIGG Bridge Engineers and MCM to the origin of the distress mechanism that was
causing the cracking and the rapidity of cracking progression.
16. Louis Berger was not qualied by the Florida Department of Transportation to conduct an independent
peer review and failed to perform an adequate review of the FIGG Bridge Engineers design plans and to
recognize the signicant under-design of the steel reinforcement within the 11/12 node, which was unable
to resist the horizontal shear between diagonal 11 and the bridge deck.
17. FIGG Bridge Engineers’ failure to adhere to the Florida Department of Transportation Plans
Preparation Manual requirements for a complex category 2 bridge structure within its work proposal to
MCM, calling for an independent rm to conduct a comprehensive peer review, led to the inadequate peer
review performed by Louis Berger, which failed to detect the under-design of the bridge.
18. Had the Florida Department of Transportation Plans Preparation Manual called for all nodal forces of
category 2 bridge structures to be checked and veried by a qualied independent peer review, this
collapse might have been prevented.
19. As part of its oversight of local agency program projects and new construction, the Florida Department
of Transportation should have veried Louis Berger’s qualications as an independent peer review rm for
complex bridge design–concrete upon receiving the 100 percent certication letters for the bridge
foundation, substructure, and superstructure plans.
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20. FIGG Bridge Engineers did not perform its due diligence when it contracted with Louis Berger for the
independent peer review of the highly complex and uncommon concrete bridge design.
21. The restressing of member 11 was a manipulation of loads that constituted a change to the FIGG Bridge
Engineers design, and, before being implemented, should have been independently peer reviewed and
signed and sealed by a professional engineer.
22. The structural cracking and northward dislocation of the upper part of the member 11/12 nodal region,
as documented in the days leading up to the collapse, was strong evidence that the structure was
progressing toward failure; and the detensioning of the 5 post-tensioning rods located in member 11
signicantly increased the damage to the member 11/12 nodal region.
23. Although the FIGG Bridge Engineers engineer of record and design manager were engaged by MCM to
assess the increased cracking of the structure, they neither recognized that the singular load path in this
nonredundant bridge had been compromised nor took appropriate action to mitigate the risk of failure.
24. Beginning with the cracking identied on February 24, 2018, the distress in the main span structure
was active, continued to grow, and was well documented by all parties involved in the design, construction,
and oversight of the bridge.
25. Neither Florida International University, MCM, FIGG Bridge Engineers, nor Bolton, Perez and
Associates Consulting Engineers took the responsibility for declaring that the cracks were beyond any level
of acceptability and did not meet Florida Department of Transportation standards.
26. Under the terms and conditions of the contract, Bolton, Perez and Associates Consulting Engineers had
the authority to direct or authorize partial or complete road closures as necessary, acting in concert with
the Florida Department of Transportation and Florida International University; however, none acted to
close the road under the bridge, contributing to the severity of the impact of the bridge collapse.
27. Local agency program agreements require stronger language to clarify that the certied local agency
has the authority to immediately close a bridge when structural cracks are rst detected or in situations
that require further investigation to protect the health, safety, and welfare of the public.
28. Given the pedestrian bridge’s unique, nonredundant design, the Florida Department of Transportation
should have ensured that the local agencies involved in the project had adequate staff who were trained
and experienced in administering these types of uncommon bridge designs.
29. The Florida Department of Transportation should have provided greater oversight of this complex local
agency program project to ensure that all safety issues were identied and addressed.
30. Given the serious consequences of the error made by FIGG Bridge Engineers in assuming that the
bridge had a redundant design, when it did not, and the current lack of guidance concerning redundancy
design in concrete and pedestrian bridges, design specication publications for concrete and pedestrian
bridges should be revised to include redundancy guidance.
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Scott Judy is Deputy Editor for Regions, and editor of ENR
Southeast, one of Engineering News-Record’s 10 Regional
publications. His roughly 27 years as a construction journalist
began with an 11-year stint covering Midwest construction
projects. In 2000, Judy helped launch the publication now
known as ENR Southeast. He often delves into controversial
aspects of the construction industry such as bankruptcies and
fatal accidents, and wishes he would never have to cover
another accident but suspects that he might.
Tom Ichniowski has been writing about the federal
government as ENR’s Washington Bureau Chief since the
George H.W. Bush administration, and he has covered at least
ve major highway bills. A recognized expert on government
policy on infrastructure and regulation, Tom is also a
Baltimore native and Orioles fan who grew up rooting for
Brooks and Frank Robinson. He is a graduate of Columbia
College and Columbia’s graduate school of journalism, where
he once used “unrelentless” in a headline.