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 ...
It was reported in the media on Thursday that the concrete was light weight. The concrete mixes I've worked with were made high strength by increasing the cement content. These mixes usually have smaller size aggregate for precast units to be post-tensioned. But honestly, I'm not experienced in the mix design, although I have heard of high strength, light weight concrete. What I've read indicates that with certain admixture, and plasticizers, cylinders can yield a 365 day strength of over 9,000 psi, but 28 day strength is lower than 1,000. I don't really know what state of the art is. I repeat, that Florida is not known for having high quality local aggregate.
MCM Construction Management is Miami based and operates across the country as well as in Florida. They are ranked 235th in Engineering New-Records’ list of the largest 400 contractors by annual revenue in 2017. That is certainly large enough for a bridge contract of this size.
Top photo of bridge makes a lot of sense to this non-engineer and is more appealing to the eye.
Nah, the government solution would be to build a light rail line that requires subsidies to cover the fares. Eminent domain, here we come!!!!
Disclaimer: this is merely a retired carpenter's guesstimate re the maximum total mass of pedestrians on that bridge at a given time.
Gleaned from a couple different sources that the ped span was 175 ft long x 40 ft wide.
Assume an area occupied by the average pedestrian at 2ft x 2ft (4 ft^2), and an average mass of each ped at 150 lbs.
+ 175 bridge length (ft)
* 40 bridge width (ft)
-----------
+ 7,000 bridge area ft^2
/ 4.00 avg area ft^2 each ped
-----------
+ 1,750 max # peds @ 4 ft^2 each
* 150 avg mass per ped (lbs)
-----------
+262,500 total max ped mass (lbs)
There are cables that run in sleeves through the concrete.
OK, Money is usually the answer to a management trying to get ahead by skipping obvious safety precautions, but in this case I suspect that they will determine that laws were also broken by this lamebrained move to leave traffic on the highway.
When the Highway Patrol needs to remove debris from the road way, they often completely stop traffic.
It is not enough to say it costs too much to stop traffic for a while, they could easily have told the city that this was their (the city’s) responsibility. The city would have to manage without the roadway for a few days, and the cost to the project management should not be affected.
The risk of a collapse was probably considered very low, but was highest during the first few hours when testing and re-tensioning the stress cables. The severity of a collapse was not too severe if traffic was restricted from using the roadway, but with cars under the structure the severity was astronomical. This was not a hard call for a reasoning manager to make.
This entire episode is positively third world.
Surely the department head was a licensed PE! Saw an article where he had a lot to do with the design. See a lot of messy lawsuits coming.
I noticed that as well. Didn’t look like much rebar and a lot of crumbled (not broken) concrete.
This one might be of interest then.
Maybe it was built and constructed by illegals and Mexicans who can’t read and understand English very well (like in LA area). (Or am I being “racist”)
How much you want to bet that they went up there to see the crack that had formed when they moved it?
... the role of failure in successful design.
I don’t know if you have read enough to know it was built 90 degree to the highway on two multi-wheeled supports that appeared to be a quarter the way from the ends. That would make for a balanced/even load when built and moved. Sitting on the ends would be a completely different load on the tension cables.
The article states they were adjusting them. If they got one or more to tight and one broke, could that cause what happened? BVB
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