Posted on 03/16/2018 12:25:26 PM PDT by C19fan
Engineering experts say investigators looking into the collapsed ‘instant’ bridge in Miami 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.
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.
(Excerpt) Read more at dailymail.co.uk ...
“You muster made it ta third grade ...”
“Thet there was the best four years o’my life, no lie!”
LOL!
With no engineering background at all, my first thought at pictures was that it looked like a cantilever bridge with no real support
Bottom run of the concrete cantilever suffered a cable tension loss?
If that's true, it should have been checked on the ground and tensioned there, when the span wasn't under stress from its own weight. Or, the tensioning should have been double checked while the span was still supported. Or so it seems to me, in my armchair analysis.
Of course, if they only discovered it after the span had been placed and the mobile supports removed, the span was likely doomed anyway.
This would use ferrules gripping the ends of cables which freely runs through individual pipe ducts, retaining an applied tension loading upon the concrete beam end-caps? The ferrules nest into forcing-cones in end plate assemblies, which would evenly transfer tension from the cables to the beam ends, thus ensuring the bottom concrete remained in compression end-to-end?
This nugget in the RFP tells us why the road was open.
3. Traffic Control Restrictions:
Lane closures shall occur only during non-peak hours on non-event nights. Non-peak hours are 9:00PM to 5:30AM Sunday through Thursday and 11:00PM to 7:00AM on Friday and Saturday Nights. A lane may only be closed during active work periods. Pacing Operations will be allowed during the approved lane closure hours. All lane closures, including ramp closures, must be reported to the local emergency
agencies, the media and the OWNER. Also, the Design-Build Firm shall develop the Project to be able to provide for all lanes of traffic to be open in the event of an emergency.
I suspect that Tamini Trail is very heavily used and there are probably no go detours. Local govt dictated that traffic should be minimally impacted. Maybe even the state.
My opinion is that for the most part this bridge was not going to solve the problem they were looking to solve. That is to provide a safe passageway that people would used. Unless you put up barriers to pedestrians on the streets, they will still use the fastest and most direct route. In creating this preferred alternative route they were/are going to create obstacles to use. They wanted it to become an “event space”. How would people cross if such space was being used and passage blocked. It certainly would limit the types of events.
It would have been far cheaper to build drop gates such as at rail crossings creating safe passage lanes. But that would not be sexy.
Lastly, the max of the bridge contract is $9,388,076. The rest of the $15 is for other costs. You can’t build bridges for that amount.
https://www.chronicle.com/article/Engineer-Connects-His-Research/142787
...I’ll use the continuous monitoring of construction and performance of the new bridge in assignments for my engineering students. They’ll observe how bridges behave under daily temperature changes, under their weight load, and so on. It’s really going to be a live laboratory.
I hope they’ll come to share my interest in bridges. I developed mine when I was young, in Iran. I wanted to do something new dealing with infrastructures and buildings and bridges. At 17, I came to the U.S. for college. After getting my undergraduate degree from the University of Oklahoma, I worked in Charleston. Then I attended the University of South Carolina, where I got my graduate degrees. All my degrees were in the steel-structures area. I then worked for Construction Technology Laboratories, in Skokie, Ill., which is associated with the Portland Cement Association and is known for concrete...
http://www.freerepublic.com/focus/f-news/3640287/posts
An engineer called the Florida Department of Transportation 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.’
https://www.enr.com/articles/44155-bridge-collapse-at-florida-university-kills-six
State and local officials said Friday that the cables supporting the deck of the pedestrian bridge at Florida International University near Miami were being tightened after a stress test when the bridge collapsed over traffic, killing at least six people.
Miami-Dade Mayor Carlos Gimenez said crews had conducted the stress test on the span earlier in the day, and Sen. Marco Rubio tweeted that the engineering firm involved had ordered the tightening of cables that had become loosened, the Associated Press reports. “They were being tightened when it collapsed,” Rubio said.
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Sounds like a possibility.
That would thrust it to one side or the other.
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who put that collage together?
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28 day breaks for even a shoddy 6 sack 3/4 max mix will usually come in around 3600.
1000 psi concrete could be broken with a baseball bat.
Small aggregate low moisture plasticised mixes are usually used when it is to be pumped.
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IMO this is a ridiculously elaborate and ostentatious
bridge for an overhead walkway.
Bragging rights for the School’s Engineering Dept
The blame is on dozens of people at least. There are so many people involved in the design, planning, construction, inspection and testing... I can’t believe this wasn’t prevented. How many people raised their hand at one of the meetings and said “hey, maybe we should have some sort of temporary support until the permanent support is in place.” It HAD to at least be a subject of debate. Especially considering it’s a CONCRETE bridge. I am completely dumbfounded and sickened. So preventable.
Maybe, if it was designed by a normal engineering group.
But, it seems this was designed by some sort of university consortium set up to do things quickly.
Perhaps detailed discussion from graduate students was simply overridden by Ivory Tower professors?
Could it be that if the concrete had been allowed to cure longer by the side of the highway, the bridge (minus cable stays) would not have pancaked?
Thanks! You have the experience! As for me with just common sense I can see this taxpayer funded, ornamental bridge, for FIU to brag about needed shoring up. That it should not have been left “naked” until cable stays were installed.
I will admit that if I drove by this bridge pre-collapse, I would have accepted -trusted that there was enough good design and engineering for it to be OK for a few weeks-months without the cable stays being installed.
Don’t know, saw it in another thread.
I have no idea how long they let the concrete cure. The rule of thumb is for one month, 30 days, and the way you let it cure also affects the hardness. Keeping concrete moist/wet while it is curing makes it much harder. I learned that when I was a kid way before I was actually trained/certified to do that kind of stuff as my Dad was an engineer and an architect and I helped him pour footings, driveways, and such for or family and ourselves.
Reading through all the different threads here on FR it seems there was no re-bar in the concrete and that just seems really dumb. no matter how hard concrete becomes it just cannot take loads without some kind of support, reinforcement, or both. I know it was tensioned but, as we can see, that didn't do too well.
Why the builder thought it was an OK idea to put that part of the bridge up either without the cable stays or temporarily shoring it where the road median was I have no clue.
https://www.chronicle.com/article/Engineer-Connects-His-Research/142787
Atorod Azizinamini, 57, is director of the Accelerated Bridge Construction University Transportation Center, at Florida International University, and a professor and chair of civil and environmental engineering there. A university-led partnership recently won an $11.4-million grant from the U.S. Department of Transportation to make it easier to get from the university to neighboring Sweetwater and other parts of Greater Miami. Mr. Azizinamini is lending his expertise on principles of accelerated bridge building for part of that project, an innovative pedestrian cable bridge that will connect the campus and Sweetwater. Here he explains the project and his role...
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