Ethics Essay

5/17/2019 Spreading Cracks On FIU Bridge Failed to Alarm Project Team | 2019-05-16 | Engineering News-Record

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May 16, 2019

Scott Judy and Richard

Korman

Structural Failures

Spreading Cracks On FIU Bridge Failed to Alarm Project Team

The plans for Florida International University's pedestrian bridge included an innovative design approach by FIGG

Bridge Engineers. (Image courtesy National Transportation Safety Board)

On the morning of last year’s Florida International University pedestrian bridge collapse, when the engineer of record assured project team members

that there were no safety risks related to cracks propagating across a part of

the unusual single-truss structure, other project team members voiced mild

concern, but no alarm. In hindsight, considering that the bridge had no inherent structural redundancy as

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“Do we need temporary shoring?”

– FIU bridge inspection company at

meeting hours before the March 15,

2018 collapse

it sat, incomplete, straddling a busy highway—and would suffer a sudden, catastrophic and deadly collapse

just hours later—the team’s lack of urgency remains puzzling, say engineering experts contacted by ENR

for comment.

Minutes of the meeting in the contractor’s �eld of�ce recently

released by the Florida Dept. of Transportation show that

attendees offered modest suggestions and questions to FIGG

Bridge Engineers.

Bolton Perez & Associates, the project’s construction

engineering and inspection contractor, asked, “Do we need

temporary shoring?,” for instance. FIGG of�cials responded that

it was not necessary. Instead, the minutes show that FIGG staff suggested that steel channels and post-

tension bars would “capture some of that force which is better than vertical support. The diagonal member

is what needs to be captured.” To the suggestion that another engineer should peer review the bridge’s

cracks, FIGG concurred.

An of�cial with FIU asked a representative with Bolton Perez their opinion of FIGG’s presentation analysis.

Bolton, Perez said they could not comment at the moment, but would “expedite” a response in 2-3 days,

according to the notes.

An FDOT representative asked FIGG to supply a copy of the presentation for the agency’s records.

 

Puzzled by Cracks

Engineers asked by ENR to review the meeting presentation and minutes for this story don’t believe that it shows exactly what errors or mistakes precipitated the sudden collapse.

Designed with a single central, open truss, the pedestrian bridge structure featured a narrower top chord.

The top chord was to serve as a canopy over the wider bottom chord, which would be the walking surface.

Cables from a 109-ft-high central pylon, not yet built at the time of the collapse, would add stability,

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according to the design-build proposal. The concrete deck was designed with two-way post-tensioning

tendons.

At the time of the collapse, contractors were apparently adjusting a tension rod in one of the diagonal

struts between the chords at one end of the bridge. It is possible that the project’s prime contractor, MCM,

and its post-tensioning subcontractor, in attempting to �x the problems, made an error that caused the

bridge’s single truss to crack and give way. According to the National Transportation Safety Board, crews

reportedly had been re-tensioning diagonal member 11 at the time of the collapse. Lacking redundancy,

the truss failed at that end and fell to the ground, smashing autos and claiming six lives.

Just days before the meeting, the truss structure cast alongside the road was loaded onto its permanent

supports and inspections showed no distressed members. But two days before the collapse, MCM emailed

FIGG about cracks. FIGG responded by instructing MCM to install temporary shims in the base of a pylon

directly below the portion of the bridge with the cracks, between the permanent support shims.

Then, on March 15, 2018, engineers, contractors, consultants, state DOT representatives and of�cials with

FIU, the project owner, gathered to hear why the bridge designer thought cracks were occurring around

part of the structure’s walking surface. The section in question was the bottom chord of the concrete truss

comprising the bridge, at one of the diagonal web members at the structure’s north end.

Meeting notes indicate that it was known that cracks were “growing daily.”

Despite that, FIGG Bridge Engineers assured project team members that they saw “no safety concern” due

to the cracking. According to the meeting notes, FIGG’s lead technical designer Denney Pate—who led the

presentation, according to FIU—and bridge engineer Eddy Leon were on site for the presentation. Dwight

Dempsey, FIGG’s design manager, joined by phone.

Team members in attendance probably held Pate’s opinion in high regard that morning. FIGG-MCM’s

design-build proposal lists numerous accolades for Pate in support of its description of him as “one of the

leading bridge designers in the world.”

A slide from FIGG’s presentation summarized the �rm’s conclusion: “After about an hour of review and

evaluation, FIGG had conducted suf�cient supplemental/independent computations to conclude that there

is not any concern with safety of the span suspended over the road.”

Responding to ENR’s request for comment, the Tallahassee, Fla.-based engineering �rm would not

elaborate on the above quote, instead stating: “The most important thing is to arrive at the truth. The

complex investigative analysis of the construction accident is ongoing. It is inappropriate to speculate on

potential outcomes with limited available information. The NTSB process precludes us from comment on

investigative information until the NTSB process is complete.”

Failure to Protect Public Safety

In retrospect, the reviewing engineers all wonder why concerns raised by Bolton Perez didn’t trigger alarm, and why no one on the project team insisted the busy road beneath the partly complete bridge be

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shut down.

Richard Rice, a certi�ed forensic engineer and president with Mutual Engineering, Hampton, Ga, said that

he’s “been in that meeting” discussing mysterious cracking, citing his involvement with the shutdown of a

parking garage at Harts�eld-Jackson Atlanta International Airport in the late 1980s, over what turned out

to be minor surface cracking in some precast double-tees.

The �rm he was working for at the time stopped work “because we had a duty to protect life and property.”

By comparison, the cracks occurring on the FIU bridge “were astonishing” in size, Rice says.

William L. Gamble, professor emeritus of civil and environmental engineering at the University of Illinois

in Urbana, told ENR that he was “dumbfounded, greatly surprised and appalled” at the documents

detailing the meeting, adding: “Yes, reinforced concrete structures often crack, but no, the cracks should

not be large and growing day by day.

“I still �nd it hard to believe that anyone who had taken, and passed, a course on reinforced concrete

design and behavior could not be greatly concerned,” he added. “Cracks that one can stick the end of a tape

measure into are a collapse waiting to happen.”

Martin E. Gordon, a forensic engineer and professor in the Rochester Institute of Technology's College of

Engineering Technology, says speculation about what happened can be dangerously misleading and any

conclusions should await the publication of detailed analysis by forensic engineers.

Gordon, however, adds that he is interested in why the design and construction team didn't shut the road

beneath the bridge. “It would still be important to review the details of what caused them to make that

decision, but on a personal basis I don’t understand why they didn’t isolate that bridge.”

Unusual Design

Rice, the Georgia forensic engineer, remains most perplexed over the designer’s use of a single truss. “That just blew me away,” he says. “To have a single truss like that is violating one of the �rst tenants of

structural engineering—provide redundancy. If you're going to make a truss bridge, you have at least two

trusses,” he argues.

In November, the NTSB issued an investigative update stating that "errors were made in the design of the

174-foot span and cracking observed prior to the collapse is consistent with those errors."

The update stated: "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 Federal Highway Administration’s Of�ce of Bridges and Structures

conducted the design review on behalf of the NTSB’s investigation.

The NTSB says major investigations such as this one normally take 18-24 months to complete, which

would mean later this year or early 2020 before its �ndings are made public.

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Recent Articles By Scott Judy

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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.

Deputy Editor Richard Korman, who has edited ENR's Risk Review newsletter since 2012, helps run ENR's business coverage, selects ENR's commentary and op-ed viewpoint submissions and oversees editorial content on ENR.com. He is currently on a part-time fellowship with the McGraw Center for Business Journalism at the Craig Newmark Graduate School of Journalism at CUNY. In 2015 he won the Timothy White Award from American Business Media for investigations of individual surety fraud and workplace bullying. Richard's freelance writing has appeared in the Seattle Times, the New York Times, Business Week and the websites of The Atlantic and Salon.com. He admires construction projects that �nish on time and budget, pay before the earth completes its annual orbit of the sun, record zero injuries and assign risk to parties who control an activity or willingly �nance the risk.

The Occupational Safety & Health Administration, meanwhile, has completed its investigation into the

causes behind the collapse, sources say, but is waiting to release its �ndings until the NTSB completes its

work.

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