^The Hyatt collapse occurred while I was in grad school. That case still scares me to death, because the problem was the engineer not reviewing changes to the job carefully enough. Of course, he was still 100% at fault, but it is SO easy for me to see this happening. Changes happen at such a rapid rate during the shop drawing/construction process that it’s quite challenging making sure the structure is still OK. 
I’ll always remember my kids’ 6th grade class where they had to team build a bridge/archway out of toothpicks to see how many text books they could hold. (Awards/crushing was on Parent’s Back-to-School Night.). Anyway, the teacher always mentioned that back in Roman times, Ceasar (I think) required the then-architects and builders to be the first to walk under any newly build structure.
back topic: today’s WSJ says that the pedestrian bridge was being “adjusted” when it collapsed. Evidently the cables had “loosened” and the builder required that they be “tightened.”
Can’t believe that they would not block off the street while that was going on…
One of the articles mentioned that they might have been adjusting the camber. When a beam or truss is put into place it will sag somewhat under its own weight alone. In order to end up with the beam level, you can have it bowed upward slightly (cambered), so that when it deflects downward it will end up straight. Perhaps they were trying to add to the camber, if the cables had relaxed enough to allow too much deflection.
Most cable-stayed bridges don’t also have trusses, so perhaps the trusses were designed to provide the support for the slab and roof during the construction, with the tower and cables providing the structural support elements after everything was in place.
While construction issues are usually up to the construction company, I did have a pedestrian walkway that we provided very explicit instructions for because it had to be assembled in a certain order. We didn’t want to leave it up to them to figure out, I guess.
I actually doubt it.
The guys interviewed in this article agree with my observation, which certainly didn’t take an engineer to see.
The inexplicable question is why the bridge span was put into place without its designed support being ready. The entire reason that bridges have to be suspended is that they can’t support themselves if they are made from those materials (concrete).
I’m tempted to say that anyone who’s ever used a wrench or a screwdriver could have seen that that span was too long to be self-supporting, but given that they put it up without the supports, I’m apparently mistaken.
^If the trusses were there to support the span, then it WAS designed to span without the tower and cables, at least until it was assembled into place. One could design a concrete truss bridge that didn’t NEED a tower and cables, although most trusses are made of steel, which is rather more practical in that instance.
It would be impossible to determine simply by looking at it that the span was too long, and we don’t know that this was the problem. In all likelihood, it wasn’t.
If it was designed to use suspension cables, it must have had a pretty low safety factor without the cables, or a temporary central support. It would be interesting to see the configuration of the steel in all that concrete.
The bridge as depicted in that USA Today article is how it was supposed to look when it was done. The portion that was erected last weekend only spans the roadway, not the lake area beside the road. The central tower in that picture is between the roadway and the water. The bridge that collapsed was about half of what the entire structure was going to be. Look at it in this picture and you can see where the water is.
http://www.mcm-us.com/projects/road-bridges/road-and-bridges-fiu-pedestrian-bridge
I am 100% positive they will discover what went wrong.
^I agree. They’ve brought in forensic experts. These people know what they are doing.
Its very interesting. The USA article that I linked to earlier has been modified. They are now saying that the tower and cables were cosmetic and that the “trusses” on the bridge itself should have been able to support the bridge. Excuse me for not buying that. They also removed the quote from the professor that said that the investigation wouldn’t take long…there were glaring obvious issues.
What are you seeing that leads you to doubt that? Is there something specific about the design you are questioning?
@dadx, you have lay people trying to write about technical issues. They’re going to get things wrong even after speaking with experts.
ANY time I have read a newspaper article on a subject about which I have personal knowledge, there is ALWAYS at least one error. I’m not surprised there are already corrections being made.
“ An engineer reported cracks on a newly installed pedestrian bridge two days before it collapsed on a busy roadway here, killing at least six people, state officials said on Friday.
The report, by the lead engineer with the company in charge of the bridge’s design, was made in a voice mail message left for a Florida Department of Transportation employee. That employee was out of the office, however, and did not receive it until Friday, a day after the collapse.
The cracking was on the north end of the span but the company did not consider it a safety concern, according to a recording of the message released by the Transportation Department.
“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,” said the engineer, W. Denney Pate. “Although obviously the cracking is not good and something’s going to have to be, you know, done to repair that.”
The transportation department said on Friday that “the responsibility to identify and address life-safety issues and properly communicate them is the sole responsibility of the F.I.U. design-build team,” referring to Florida International University, which commissioned the bridge.”
Ain’t THAT the truth, @MaineLonghorn!? I’m a practicing chemist, and almost every time I read an article or see a news report about some chemistry-related-matter, I find major errors in the basic science. It’s disturbing.
^So true, and in this case it is not surprising that people are confused as to the design intent, since one does not usually see both trusses and cables in the same structural design function.
Based on my many years of performing engineering investigations, plus my near complete ignorance about bridges and concrete, I am willing to bet the mortgage that the cracks reported had absolutely nothing to do with the failure.
The only information that makes it to the public domain quickly after a disaster that is factually correct is “something bad happened.” Everything else is noise and fog.
This isn’t a cheap novel about heartless designer engineers and greedy contractors. Investigators actually want to know what went wrong so it won’t happen again, and they will keep pushing until they find out. Lawyers and insurance companies want to know so they know who to blame and what to require to cover future risks. Designers and builders want to know so they don’t have to try to sleep at night after this happens on one of their projects. And in the process a barrel full of red herrings will be tossed about. And future bridges will be safer.
What happened this week in Florida is horrific, and I can’t imagine the heartbreak of the victims’ families. But if the answer were obvious it wouldn’t have happened. So we’ll all have to wait for the people with both expertise and access to the design and construction details to wade through the data and figure it out. Frustrating, but there’s nothing else for most of us to do.
Of course we can’t know what happened, or know motivations or decisions that were made. We will not know for a long time.
However, I have to counter the idea that unquestionably dangerous and potentially criminal decisions are never made by those in charge. Look up Buffalo Creek. Look up Bhopal. People in decision-making positions make choices that are clearly cutting corners all the time. How do they sleep? I have to assume that when they make these decisions, they cross their fingers and lie to themselves–that nothing dangerous will happen. That no one will die.
I have no idea if anything with this bridge is because of cost/corner cutting decisions. We won’t know for a long time. But I just can’t accept the statement that people don’t make dangerous, cost-saving decisions in real life. Of course some do.
Yes, I agree.
Of course people make cost cutting decisions, on even the most successful projects. Every major project has risks. They go forward because teams of analysts agreed that the risks had been mitigated. In this case, either a risk did not get properly identified,or did not get properly mitigated. I do have confidence that the investigation will identify the cause, and that it will also identify a lot of other things that happened in the decision making process.
There is negligence and there is criminal negligence.
Oh @scout59 - I am with you on science reporting. Sigh.