An engineer called the Florida Department of Transportation (FDOT) to report concerns about a crack on their new 'instant' bridge two days before it collapsed - but no one ever picked up their voicemail.

FIGG's lead engineer responsible for the Florida International University (FIU) pedestrian bridge project, W. Denney Pate, left a message warning that they had observed some cracking at the north end of the bridge. The voicemail was not picked up until Friday - a day after the bridge collapsed killing six.

Pate warned that the cracking areas would need repairs but assured that, 'from a safety perspective we don't see that there's any issue.'

An engineer called the Florida Department of Transportation to report concerns about a crack on their new 'instant' bridge two days before it collapsed (pictured before the collapse)

‹ Slide me › FIU's pedestrian bridge (left) was on schedule to open to foot traffic in 2019. It was installed last Saturday (right) even though it had no central support tower or stay cables in place

The graphic above shows the missing parts of the bridge which were yet to be built

Two days later it fell, crushing eight cars underneath and killed six people

Aerial view shows a pedestrian bridge collapsed at Florida International University in Miami, Florida

He ended the call, urging the employee to 'call me back when you can' to discuss the problem.

The message was not picked up by an FDOT employee until Friday as the staff member was out of the office on assignment.

FDOT have since released a statement placing the blame squarely on the shoulders of FIU.

'The responsibility to identify and address life-safety issues and properly communicate them is the sole responsibility of the FIU design build team,' the statement read.

'At no point during any of the communications above did FIGG or any member of the FIU design build team ever communicate a life-safety issue.

'The tragic failure and collapse of the pedestrian bridge at FIU is the subject of an active and ongoing investigation led by the National Transportation Safety Board (NTSB) as well as local and state law enforcement investigations. As FDOT assists in these investigations, we will continue our internal review and release all pertinent information as quickly as possible while ensuring its accuracy.'

The revelation comes after Miami-Dade County Commissioner said he was shocked to discover that the busy seven-lane freeway underneath the bridge wasn't closed while stress tests were performed.

THE ENGINEER'S VOICEMAIL IN FULL The voicemail, obtained by ABC, was left on a landline of an employee at Florida Department of Transportation by W. Denney Pate, FIGG's lead engineer responsible for the FIU pedestrian bridge project. Hey Tom, this is Denney Pate with FIGG bridge engineers. Calling to, uh, share with you some information about the FIU pedestrian bridge and some cracking that's been observed on the north end of the span, the pylon end of that span we moved this weekend. Um, so, uh, we've taken a look at it and, uh, obviously some repairs or whatever will have to be done but from a safety perspective we don't see that there's any issue there so we're not concerned about it from that perspective although obviously the cracking is not good and something's going to have to be, ya know, done to repair that. At any rate, I wanted to chat with you about that because I suspect at some point that's gonna get to your desk. So, uh, at any rate, call me back when you can. Thank you. Bye Advertisement

Commissioner Xavier Suarez, who has a background in civil engineering, said he was flabbergasted that the street was not shut down to traffic before or during any stress tests or cable adjustments on the unfinished project

Named: Alexa Duran, an 18-year-old FIU freshman (right), and bridge worker Navaro Brown, 37, (left) are among the six victims of Thursday's fatal pedestrian bridge collapse

Commissioner Xavier Suarez, who has a background in civil engineering, said he was flabbergasted that the street was not shut down to traffic before or during any stress tests or cable adjustments on the unfinished project.

'Never in my life have I heard of that,' Suarez said. 'That makes no sense. That makes no sense.'

'As a public official, I am saddened by the FIU bridge collapse. As an engineer it baffles me that a brand new bridge with no unusual (or, possibly even expected) loads could collapse in that way. Our prayers are with the victims and their families.

'Collapse of a brand-new pedestrian bridge w/o pedestrians on it @ FIU makes no sense. I will not accept explanation based on 'testing.' U cannot 'test' bridge when people are driving below it.

'I want 2 know what failed - support or span? Either way, somebody was beyond negligent.'

He isn't the only person demanding answers to why the highway wasn't closed at the time of the tests.

The crushed Chevy van seen above belongs to Structural Technologies, a national company that offers engineering services

Miami-Dade Fire Rescue Department workers work at the scene of the collapsed bridge. A vehicle which appears to be a white van is seen on the left after it was crushed by the bridge. The van belongs to an engineering firm whose employees were working on the site

Sen. Marco Rubio, the bridge's internal support cables were being 'tightened' just as the bridge crumbled onto traffic below, crushing eight cars under 950 tons of concrete and steel.

But no one has yet explained why cars were allowed to drive freely under an incomplete bridge while workers were testing to see if it might fall apart. Now, some local officials are demanding answers.

The City of Sweetwater insists said it had no say in who built the bridge - claiming the decision was made by Munilla Construction Management (MCM), and the Florida Department of Transportation (FDOT).

'We were never involved in any decisions about the streets,' said spokesman Sandy Antonio. 'The construction company worked directly with FDOT on getting approval to shut down the street.'

SW Eighth Street was closed 9pm Friday until 5am Monday, while the bridge was swung into place last weekend, using FIU's Accelerated Bridge Construction.

FDOT had informed Sweetwater about the closures ahead of time.

'The only involvement we had was understanding when it was shut down and when it would reopen,' she says. 'That was all determined by the construction company and FDOT.'

Yet there were no such arrangements for the day of the testing.

Engineering experts say investigators looking into the collapsed 'instant' bridge at Florida International University will want to know why a central tower which is usually built to support a suspension bridge was not in place when it collapsed onto Tamiami Trail on Thursday afternoon

Dr. Amjad Aref, a civil engineer and researcher at the University of Buffalo's Institute of Bridge Engineering, told the New York Times it wasn't unheard-of to let traffic flow during a stress test under some conditions.

But where a bridge is incomplete, the public are generally kept out of the way.

'Normally when we do anything, even a fairly completed bridge or if it's some rehab or even really minor load-testing, there's some sort of traffic control,' Aref says.

He added that many bridges are typically tested in a lab setting before being installed.

But it's unclear what precautions were in place before the accident.

Investigators are also looking into why the 'instant' bridge, which collapsed killing six on Thursday in Miami, was not supported by a central tower when it was tested yesterday.

Last week, Florida International University's official Twitter account posted a rendering of the bridge in its completed form as envisioned by the planners before its opening to foot traffic in early 2019.

The rendering shows a tall central column with cables connecting it to the main span.

Engineers say the design is known as a 'cable-stayed bridge,' which is a kind of suspension bridge, according to USA Today.

The FIU bridge was not yet open to the public when it collapsed onto the eight-lane highway below, killing at least six people and injuring at least 10.

Last week, FIU's official Twitter account posted a rendering of the bridge in its completed form as envisioned by the planners. The rendering shows a tall central column with cables connecting it to the main span. The city of Sweetwater also released a rendering above

The FIU bridge was not yet open to the public when it collapsed onto the eight-lane highway below, killing at least six people and injuring at least 10. It is seen above after it was installed last Saturday and before its collapse on Thursday

The bridge did not have the central tower in place, even though experts say it is usually placed at the early stages of construction.

In the absence of a tower, there is usually a temporary support, though in this case it is unclear what the builders were using in the absence of a central structure.

'Whoever is going to investigate, they will ask the fundamental question: shouldn't the tower be there, and the cables ready to connect to the structure, when you lift it?' said Amjad Aref, a professor at University at Buffalo's Department of Civil, Structural and Environmental Engineering.

'That's a question for them to answer.'

Cable-stayed bridges are built in stages. First, planners will locate a clear piece of land with stable ground and a good location.

They will then conduct a subsurface investigation which involves lab testing on the soil to make sure that any proposed structure would be supported by the geological conditions at the site.

If those tests permit, engineers would then erect piers – the upright supports for a structure like a bridge or an arch - and the support span.

After building the main piers, engineers usually begin construction of the central tower.

After the tower is built and the stay cables are installed, engineers then begin work on extending the central span.

When asked about why there was no central column built before the span, the head of the National Transportation Safety Board, Robert Sumwalt, said: 'That's part of our investigation.'

The NTSB is an independent federal agency that probes transportation-related accidents.

Andrew Hermann, a former president of the American Society of Civil Engineers, said it appears the engineers who built the FIU bridge didn't follow the proper sequence.

'When you're doing staged construction like this, what you have to make sure is that at each stage that the structure is strong enough for the loads that are on the bridge,' Hermann told USA Today.

'The engineering, both design and the construction engineering, should have taken that into account with the bridge in that condition.'

Engineering analysts are also vexed as to how a cable-stayed bridge built to carry pedestrians could buckle under no weight – even though a number of larger structures which can withstand cars and trucks remain in place.

'I wish I would be on that kind of investigation, to be honest with you, because in this country we build so many cable-stay bridges for carrying trucks, not pedestrians, and all of them work fine,' Aref said.

'The spans, from one end to the other, is much larger than that.'

The most popular examples of cable-stayed bridges are the newly constructed Kosciuszko Bridge, which connects two New York City boroughs along the Brooklyn-Queens Expressway.

Cable-stayed bridges (like the new Kosciuszko Bridge connecting Brooklyn and Queens as seen above during construction in 2017) usually have central towers and cables in place before the main span is completed

The Sunshine Skyway Bridge in Tampa and the John James Audubon Bridge in Louisiana are other examples of cable-stayed bridges.

The partially built 950-ton bridge had been assembled by the side of the highway and moved into place Saturday to great fanfare.

The span stretched almost 200 feet to connect FIU with the city of Sweetwater.

It was expected to open to foot traffic next year.

An accelerated construction method was supposed to reduce risks to workers and pedestrians and minimize traffic disruption, the university said.

Robert Bea, a professor of engineering and construction management at the University of California, Berkeley, said it's too early to know exactly what happened, but the decision to use what the bridge builders called an 'innovative installation' was risky, especially because the bridge spanned a heavily traveled thoroughfare.

'Innovations take a design firm into an area where they don't have applicable experience, and then we have another unexpected failure on our hands,' Bea said after reviewing the bridge's design and photos of the collapse.

Aref said he expects this to be a quick investigation.

'I don't want to speculate. From a structural-engineering point of view, the forensic engineers won't take long to figure out what happened,' he said.

The Sunshine Skyway Bridge in Tampa (above) and the John James Audubon Bridge in Louisiana are other examples of cable-stayed bridges

A spokesperson for Structural Technologies told DailyMail.com that it could not comment on what its employees were doing at the site, though it said one of its workers died and two others were injured

Arescue dog and its handler works at the scene where a pedestrian bridge collapsed to search for survivors. The Structural Technologies van is seen on the left

'I think it is not a long investigation. There are glaring things.'

Dr. Igor Belykh, an expert on pedestrian bridges who teaches at Georgia State University, told DailyMail.com that the FIU bridge collapse appears to be a 'construction accident' - though he said it was premature to definitively pinpoint the cause.

A fatality from the bridge collapse was identified by her father on Friday.

Florida International University freshman Alexa Duran, 18, was identified by her father on Friday as one of the six victims of Thursday's fatal pedestrian bridge collapse in Miami.

Duran was driving her friend and schoolmate Richie Humble back from a doctor's appointment when the structure came down on top of her gray Toyota SUV.

Humble was able to make it out of the crumpled vehicle, but he could not extract his friend, who was in the severely damaged driver's side of the SUV. Duran was initially unaccounted for, but on Friday afternoon her father, Orlando Duran, confirmed that she was among the dead.

Juan Perez, the director of the Miami-Dade Police Department, told a local radio station on Friday that criminal charges could be filed against those deemed responsible for the bridge collapse.

Perez said the first priority is to remove the debris and recover the bodies of those trapped underneath, according to the Miami Herald.

'Hopefully, this morning we'll be able to get under that bridge, remove some of the [bridge] parts and start removing those bodies,' he said.

'We just want to get those bodies out of there so [families] can have their loved ones one last time.'

Perez said that local and federal authorities will try to establish who - if anyone - is at fault for the bridge's collapse.

'We've got to look at the reality that there may be some negligence down the line,' Perez said.

'[The numerous investigations] will help determine whether someone is liable for this.

'It's obviously an accident either way. We have to look to see if somebody contributed to that accident.'

Seconds later, the bridge collapsed on the traffic below, leaving dust in its wake

This is the moment the 950-ton bridge, installed in just six hours on Saturday, collapsed on cars waiting for the lights to change

A van belonging to the engineering firm which may have been conducting a stress test on the 'instant bridge' was crushed in the rubble.

Structural Technologies, a national company which offers engineering services, confirmed that one of its employees was among at least six people killed in the bridge collapse.

Two other workers were injured and are in stable condition, the company told DailyMail.com.

A spokesperson for the firm told DailyMail.com that the company could not comment on specifically what its employees were doing at the bridge when it collapsed due to the pending investigation.

The company said it plans to fully cooperate with local and federal authorities investigating the collapse.

According to its web site, Structural Technologies offers 'post-tensioning' services to engineering firms.

Experts say that tightening steel cables on this kind of bridge has caused at least one collapse in the past, pointing to an example from Australia in the 1970s

Post-tensioning is a method of reinforcing concrete structures.

It is a form of prestressing - which means that the steel cables are stressed (pulled or tensioned) before the concrete has to support the service loads, according to ConcreteNetwork.com.

Florida International University is facing questions over whether it did its due diligence in selecting the companies to ensure that the bridge was safe.

The Florida Department of Transportation said that it was the school's responsibility to choose firms that were 'pre-qualified', according to CBS Miami.

The state agency said that the firm chosen by the school did not fit the 'pre-qualified' criteria.

FIU President Mark Rosenberg insists that the school went through the proper procedures in selecting the engineers.

'I'm satisfied that the testing that was occurring was consistent with best practice,' Rosenberg said Thursday.

Authorities said Friday that the cables suspending a pedestrian bridge were being tightened after a stress test when the 950-ton concrete span collapsed over traffic, killing six people only days after its installation was celebrated as a technological innovation.

As state and federal investigators worked to determine how and why the five-day-old span failed, Florida politicians pointed to the stress test and loosened cables as possible factors, and a police chief asked everyone not to jump to conclusions.

The rescue efforts continued through the night on Thursday as teams continued to search for survivors

'This is a tragedy that we don't want to re-occur anywhere in the United States,' said Juan Perez, director of the Miami-Dade police.

'We just want to find out what caused this collapse to occur and people to die.'

US Senator Marco Rubio tweeted late Thursday that cables suspending the span had loosened, and the engineering firm ordered that they be tightened.

'They were being tightened when it collapsed,' he said on Twitter.

The $14.2million pedestrian bridge was supposed to open in 2019 as a safe way to cross six lanes of traffic between the FIU campus and the community of Sweetwater, where many students live.

Florida Governor Rick Scott said Thursday that investigators will get to the bottom of 'why this happened and what happened,' and if anyone did anything wrong, 'we will hold them accountable.'

Rubio, who is an adjunct professor at the school, noted the pedestrian bridge was intended to be an innovative and 'one-of-a-kind engineering design.'

That tower had not yet been installed, and it was unclear what builders were using as temporary supports.

An accelerated construction method was supposed to reduce risks to workers and pedestrians and minimize traffic disruption, the university said.

The project was a collaboration between MCM Construction, a Miami-based contractor, and Figg Bridge Design, based in Tallahassee. Figg is responsible for the iconic Sunshine Skyway Bridge across Tampa Bay.

Both companies have been involved in bridge collapses before.

The brand new pedestrian bridge collapsed without warning on Thursday afternoon, crushing the cars below it

Aerial photos show the devastation caused when the structure collapsed, as multiple emergency vehicles rushed to the scene