Calculation Errors and Inadequate Peer Review Led To Miami Bridge's Collapse (ntsb.gov) 73
America's National Transportation Safety Board has now officially determined the probable causes of a Florida pedestrian bridge's collapse in March of 2018: load and capacity calculation errors made by FIGG Bridge Engineers.
Slashdot reader McGruber shares their report: Contributing to the collapse was Louis Berger's inadequate peer review, which failed to detect FIGG's calculation errors in its design of the main span truss member 11/12 nodal region and connection to the bridge deck. The FIGG engineer of record's failure to identify the significance of structural cracking observed in this node before the collapse, and failure to obtain an independent peer review of the remedial plan to address the cracking, further contributed to the collapse...
Six of the eight lanes of the roadway traveling under the bridge were open at the time of the collapse. The failure of FIGG, MCM, Bolton Perez and Associates Consulting Engineers, FIU and the Florida Department of Transportation to cease bridge work and close SW 8th Street to protect public safety contributed to the severity of the collapse outcome, said the NTSB during the meeting.
"Errors in bridge design, inadequate peer review and poor engineering judgment led to the collapse of this bridge," said NTSB Chairman Robert Sumwalt. "The failure of all concerned parties, to recognize and take action on the threat to public safety presented by the significant observed bridge structure distress prior to the collapse, led to the tragic loss of life in this preventable accident."
The report also concludes that Louis Berger "was not qualified by the Florida Department of Transportation to conduct an independent peer review" -- and that Florida's Department of Transportation "should have verified Louis Berger's qualifications as an independent peer review firm as part of FDOT's oversight of local agency program projects."
Slashdot reader McGruber shares their report: Contributing to the collapse was Louis Berger's inadequate peer review, which failed to detect FIGG's calculation errors in its design of the main span truss member 11/12 nodal region and connection to the bridge deck. The FIGG engineer of record's failure to identify the significance of structural cracking observed in this node before the collapse, and failure to obtain an independent peer review of the remedial plan to address the cracking, further contributed to the collapse...
Six of the eight lanes of the roadway traveling under the bridge were open at the time of the collapse. The failure of FIGG, MCM, Bolton Perez and Associates Consulting Engineers, FIU and the Florida Department of Transportation to cease bridge work and close SW 8th Street to protect public safety contributed to the severity of the collapse outcome, said the NTSB during the meeting.
"Errors in bridge design, inadequate peer review and poor engineering judgment led to the collapse of this bridge," said NTSB Chairman Robert Sumwalt. "The failure of all concerned parties, to recognize and take action on the threat to public safety presented by the significant observed bridge structure distress prior to the collapse, led to the tragic loss of life in this preventable accident."
The report also concludes that Louis Berger "was not qualified by the Florida Department of Transportation to conduct an independent peer review" -- and that Florida's Department of Transportation "should have verified Louis Berger's qualifications as an independent peer review firm as part of FDOT's oversight of local agency program projects."
So, they relied on friction? (Score:3)
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 sufficient capacity to counteract the demand load for interface shear – and the bridge would still have been under-designed and could have failed.
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I don't care how well engineered the polymer is or what it is filled with. I don't want glue to be used in a tensile/shearing manner to hold tons of concrete back from falling on me.
Re:So, they relied on friction? (Score:5, Insightful)
That is irrational. What matters is material properties, not whether it is "plastic".
I seriously hope you are not an engineer and never do engineering work, because you have not the first clue about how that works.
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Re: So, they relied on friction? (Score:2)
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Re: So, they relied on friction? (Score:1)
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If what is it named mattered more than what its material properties are, people like you could be engineers. In actual reality, it matters not at all whether it is "metal" or "plastic" (apparently that is the extent of your insight...), but what it actually is, what its properties are and how it is used.
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All that matters is that the lowest tender got the job and produced the outcomes you would expect from the lowest tender when it comes to engineers. Now normally when engineers win with the lowest tender, their designs are way over engineered. You do not just engineer designs you try them out, test each case, do the calculations to see if it that particular structural element will be strong enough or do another calculation for with a stronger one, until you find one strong enough, or you guess high, test th
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This is a complete misunderstanding of the way this bridge designer win tenders [heavy.com]:
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That is irrational. What matters is material properties, not whether it is "plastic".
I seriously hope you are not an engineer and never do engineering work, because you have not the first clue about how that works.
Plastic *is* a material property.
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I thought steel was the usual material to add to a design to give it tensile (pulling apart) strength. Encasing it in concrete also helps avoid its corrosion pitfall.
Here, the designers both grossly underestimated the sheer at a node where two trusses joined the bridge deck, and overestimated the strength of the interface between the trusses and the
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Steel is used because it's relatively cheap, and self-supporting in terms of shape, as you pour concrete around it. But steel has about 15% of the tensile strength of better polymers (HMPE).
The better steels do much better than that. Maraging steel has a tensile strength as high as 2400 MPa, the lower end Spectra product is about the same as this, the best UHMWPE product (Dyneema) is only about 50% greater. If you are going to use exotic polymers you should compare to exotic steels.
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....which was not taken seriously for the almost 3 weeks it took to completely fail.
Ah, the ages-old catastrophic combination of incompetence and arrogance.
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Look up "Sudaglass" for one vendor
Re:So, they relied on friction? (Score:5, Informative)
An epoxy polymer can be applied as a liquid so it fills in all gaps and spaces evenly, before hardening. This ensures maximized contact area and even distribution of stresses. The epoxy may be weaker, but its better coverage of the irregular gaps means it reduces localized stresses by a larger degree than its weakness; making it the superior material choice. i.e. The epoxy isn't acting as a glue holding the bolt into the concrete. It's acting as a cushion, helping spread the load from the bolt evenly over the concrete, so as not to fracture the concrete.
In other forms of construction, the same is accomplished by putting the metal rods in place first, then pouring the concrete around them (so the liquid concrete fills in any gaps). But that wasn't an option in the Big Dig tunnel since these were roof panels - gravity would've caused the concrete to run out from around the metal, creating more of the gaps which you're trying to prevent. Epoxy had sufficient viscosity it could be injected upward, and not run out creating gaps before it hardened.
If I remember right, the problem was they used an epoxy which wasn't rated for the humidity and cold temperatures of the New England climate.
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The "plastic" was used to interface between concrete and metal retaining bolts holding the panels up. Concrete is strong, but nearly incompressible (does not change its shape) and fractures easily when overstressed. Metal is strong, but requires high temperatures to change its shape fluidly. So how do you interface metal bolts with concrete? If you simply drill or screw the metal into the concrete, you'll fracture off small pieces of the concrete. The resulting irregular surface will provide only intermittent contact area between the concrete and metal bolt, resulting in localized regions of high stress in the concrete. That can cause more pieces of the concrete to chip away, further increasing stresses on remaining contact areas, until the whole thing fails.
Wonder if this has anything to to do with chunks of Toronto's Gardiner Expressway falling off?
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I don't care how well engineered the polymer is
Yes. Why trust sciency and engineering mumbo jumbo when you have *faith* to design buildings.
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Similar things have happened [wikipedia.org]. It never fails to amaze me either the stupidity or brazen ego of some engineers. Giant concrete slabs were held up with PLASTIC. This epoxy is OK in a lot of applications like mining, but they were using plastic to hold the fasteners in place over humans.
I don't care how well engineered the polymer is or what it is filled with. I don't want glue to be used in a tensile/shearing manner to hold tons of concrete back from falling on me.
Having just ridden some collapsing stairs last weekend, non-captive fasteners should *never* be used in tension where safety is any consideration.
That design should never have been approved for the Big Dig. I would be good with those who approved it being executed since failure resulted in deaths and injuries. The inspector general's report was a cover up.
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I Am Not A Mechanical Engineer, but quick search found this [eng-tips.com], and this [researchgate.net].
Look at Table 1 of the second link, at "u = coefficient of friction", for an interface "cast monotonically", i.e. all at once, it's one piece, then "Concrete to hardened concrete with roughened surface", and finally "Concrete placed against hardened concrete not intentionally roughened", with u steadily decreasing, it would seem to pertain to the strength of an interface. Intuitively, if cast all at once it's the strongest. If you add
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From what I have been reading on this, it sounds like it was under-designed for the interim loading condition, and non-redundant for the final condition. FIGG sounds like a complete disaster; that they were at the site hours before the collapse and thought nothing of the cracking says a lot.
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Relying on friction is not the problem. Relying on overestimated friction is a big problem.
Think about it. What holds a nail in place in a piece of wood? Friction. Same for screws, nuts and bolts. When friction is high enough and in the right direction, it can hold large loads.
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Re: "Great" American engineers at work (Score:3)
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If the bridge collapses, that is pretty much impossible to hide, even in China...
I live and work in the area, I am not surprised (Score:5, Interesting)
Sadly, this type of thing is somewhat common on the lower southern part of florida. My trade is real estate, I grew up learning construction and engineering ( better to overbuild just in case, than to build and watch it break sooner than later ) and I know about most residential building lawsuits that are happening and what was the reasons for it from a boots on the ground perspective.
Southern Florida construction practices are really good at cutting corners, for example, Stucco work has a defined parameter mix, what some sub-contractors do is add more sand to the mix and increase the volume, looks the same, acts the same and guess what, by the time you are done and gone, it's holds the same for about 3 years or so ( depending on how much sand ) but sooner or later poof.. the stucco cracks and falls from 100ft to 400ft and you get to see people run. ( to cite source Beach Club Hallandale & and near tampa, ( sorry I forget the lawsuit ) a 800 house building tract remediation of stucco class action, get your house stuccoed for free but it cost the insurance company 72 million or a number near that)
Shoddy construction cost people lot's of money in the future, and cities in the US need more inspectors and I mean Qualified inspectors that have taken a journeyman type of view for a long term profession.
Re:I live and work in the area, I am not surprised (Score:5, Interesting)
Many people suspected shoddy construction based on the sort of things you mention, but it was a design failure, very much like the I-35W Mississippi River bridge [wikipedia.org] one. Both failed because an interface between parts wasn't strong enough, the NTSB found no problems with the materials or how they were put together.
Where you might have a point is what I've in part learned from other reading [miamiherald.com], the bridge section started failing the instant concrete forms supporting it were removed, and the NTSB notes that for almost 3 weeks the engineers responsible for the bridge waved off the reports they got of it progressively cracking further and further, many times past what's acceptable.
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You make a very valid point. and to be clear, I would have suspected quality control error and skimming issues in the southern florida market before I would have thought of design error.
and yes peer review and proper reporting should be mandatory.
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Also recalls the Hyatt Regency Walkway Collapse [wikipedia.org] in that case it was not the original design that was bad (unlike with FIGG), but an informal redesign that was never properly analyzed (in this respect it was somewhat like FIGG). Like the FIGG bridge the walkway was overloaded from the very moment it was constructed - its failure was a matter of time only. In the Hyatt-Regency case it stood for a bit over a year before it failed. Since the walkway was periodically loaded by people using it (which is why it wa
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Correction: the original design of the Hyatt-Regency was bad, but the redesign made it much worse.
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HOW? the rebar is visible during the pour, then it gets covered ??? How in the heck did they pull this off??
these are people that should go to jail.
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Regarding corner cutting when say mixing stucco or concrete, a
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funny that you mention quality control... talking with a construction client, and he just became and insurance company contractor... he takes over the jobs that the insurance company has to deal with bonded contracts. real interesting because it pay's 2 times as much.
I asked will he be busy? he said, his books are full from legal work time start to legal work time end, and in certain towns, 24 hours x 7 days permits are issued. and he is full. asked me if I wanted a job.
must be a lot of screw ups
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So who is being criminally charged? (Score:5, Interesting)
Someone should be charged with criminal negligence. This is similar to the Boeing 737 MCAS debacle.
The outcome may have been unintended but it wasn't an accident. It was a foreseeable consequence given what the builders did and didn't do.
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that wasn't enough for a deliberately unique "artistic" design.
Bring back Brutalism - Brutalist design works, baby!
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The bottom, almost all the load bearing part of it that failed sure looks Brutalist to me. It's exposed concrete, whitened with titanium dioxide. One of the FIGG engineers told the construction company to not use Sharpies to point out the cracks....
With the planned fake suspension part on top of that, that's why the trusses are as such strange angles, it would have overall looked better from the outside, but anyone traveling through it would only see extra-white concrete, plus the handrails and whatever o
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The cable stays weren't fake, but the fact that they're installed after installing the concrete span means that at the stage the bridge was in at the time of collapse, none of the planned supporting forces from the cable stays were present, and the bridge had to be self-supporting without the stays. To make it stable enough for move into position, they added temporary tension to the 11th (and the 2nd) member before the movement of the span (from the side of the road to across the road), and then removed it
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Another important detail: the plan to tension the 11th and 2nd members was a late modification made when the location of the bridge was moved north on the request of FDOT: "The move forced a change in the carefully calibrated plan for moving the bridge into place. It put the north end of the main span well off the edge of the roadway on a canal bank. Because a transport machine could not traverse that roadway edge, the point where it would lift the structure was moved toward the center of the bridge. That
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In the year and a half since the article you linked to was written, we've learned the plan for moving the span was never "carefully calibrated", FIGG never bo
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They were "fake" in terms of providing serious support, mechanically they were intended to dampen harmonics and the like.
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This appears to be a straight-out design flaw. People who shouldn't been able to do certain calculations correctly, didn't. The 737 MAX case was a pr
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The engineer of record for Figg will likely go to jail on this one.
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In most countries and indeed in most states of America Engineering is a profession which is licensed, and someone is very likely going to defend themselves in court over this, and at the very least lose their license to perform their art.
And this is why... (Score:2)
Coders will NEVER become professional engineers. They will NEVER accept liability.
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I would. But you'll be paying 10x as much and waiting 3 times longer.
3x in cost and time for the additional work to ensure correctness. 3x more in cost for the increased liability I'm taking on. Plus a bit for certification and insurance costs.
klusterf... (Score:2)
There were so many errors contributing to this disaster that it makes one wonder if perhaps we have an engineering, development, and production system problem. We need to ask how so much incompetence and carelessness is making it through the system and determine whether there is a widespread issue. Was this a one-off?
Personally, I see code violations in new construction every day. Inspectors who have 5 minutes at each site rarely care about anything that isn't insultingly obvious.
Agile? (Score:2)
The question that's on everyone's mind: were these bridge designers doing Agile(tm)?
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Immediately after the bridge section collapsed, the institutions of all the strong women who had taken credit for building a strong bridge when it was put into position "clarified" the women had absolutely no role in it.
But there's no way Linda Figg escapes blame for creating an engineering conglomerate focused on art that fielded the completely incompetent team responsible for this debacle. As I've mentioned many times, according to the NTSB this was so fundamental they thought an obviously non-redundant