Pedestrian bridge collapses at FIU

[throwittoblythe]

Post-tensioning steel in concrete seems like a bad idea to me. Creating all kinds of small cracks in the concrete but I suppose with the right concrete and planning it could and does work.

The key is to integrate the concrete and tensioning design so they work together. These are not steel beams that are tensioned, they are elastic super-high-strength tendons that are stretched in (what should be) a controlled manner. A very simple analogy would be the laces on your shoes. The laces and your shoe "structure" work together to support your feet.

 

[throwittoblythe]

Yikes, that looks expensive. It appears the main supports were not sufficient as they collapsed outward and the center support comes down. After a couple more views, that center support twists a little and the first two cables to the left fail first. Possibly not balanced correctly?

This one is beyond my knowledge, but I believe there is a tension member that connects the middle of the "diamond." All that downward force from the cables is transferred into a horizontal member that is supposed to take the tension. If you look closely, or at other videos, there's a puff of dust right before it goes down which suggests that member snapped, causing the failure. It's a balanced cantilever bridge, so it's possible the bridge was not balanced properly during construction.

 

[ArgentCy]

The key is to integrate the concrete and tensioning design so they work together. These are not steel beams that are tensioned, they are elastic super-high-strength tendons that are stretched in (what should be) a controlled manner. A very simple analogy would be the laces on your shoes. The laces and your shoe "structure" work together to support your feet.

So the steel is encased in a tube and not touching the concrete and then you basically tie the concrete together because concrete is very strong in compression. Got it.

 

[throwittoblythe]

Post-tensioning steel in concrete seems like a bad idea to me. Creating all kinds of small cracks in the concrete but I suppose with the right concrete and planning it could and does work.

Also, there are two types of tensioning: POST-tensioning and PRE-tensioning. Pre-tensioning occurs when you tension the strands and then pour the concrete around them. Post-tensioning is where you pour the concrete and have open ducts for the strands. The strands are installed after the concrete is cured and then tensioned when the concrete has reached enough strength. This bridge is a post-tensioned bridge.

 

[throwittoblythe]

So the steel is encased in a tube and not touching the concrete and then you basically tie the concrete together because concrete is very strong in compression. Got it.

You got it. You tension the strands inside the ducts, as mentioned above, and then encase the strands in grout to protect them for the life of the structure. The strands give the concrete a lot of tension capability (thus increasing flexural capacity) without taking up much space. These tendons are tensioned with hundreds of thousands of pounds of force. If you were near one when it snapped, it would slice you in half in a split second.

 

[VeloClone]

Or like Iowa who used that excuse to raise the gas tax 10 cents per gallon. Gee, how many bridges are they fixing now?

Iowa didn't raise the gas tax from 1989 ($0.20) to 2002. During that time inflation would have demanded a raise of 9 cents a gallon to preserve the buying power of the revenues. From 2002 to 2008 the gas tax was raised a total of 1 cent per gallon. To keep pace with inflation to preserve the buying power a raise of about 4 cents would have been required during that time period.

All told to have the same buying power of that $0.20 from 1989 the state would have needed to have raised the rate about 100.8% or over doubled to 40.16 cents. The rate has only been raised 54% to 30.8 cents.

Minnesota was more aggressive about raising its 1988 gas rate of $.20 per gallon starting in 2008 and was up to 28.5 cents by 2012 but has stagnated there since so Minnesota is even further behind than Iowa in keeping up with inflation.

 

[jdoggivjc]

An old officer friend of mine who went SF always used to say "I take great comfort knowing that every piece of equipment I trust my life to was built by the lowest bidder."

Aren't the lowest bidders usually lowest for a reason, and not because they discovered cheaper, more efficient ways to deliver high quality?

At least in terms of the Federal government, the "lowest bidder" is usually a small business that intentionally underbids business that we know are capable of doing the job, and a good amount of the time they've underestimated their ability to do the job - and that's the "well-intentioned" businesses. You'll have other businesses that underbid just because they want the money, not giving a damn they don't have the ability to do the job. And, because they're the lowest bidder, the government is almost always obligated to go with them due to "getting the best deal for the taxpayer money". What the government doesn't always get is the lowest bidder generally isn't always the best deal.

 

[CycloneErik]

At least in terms of the Federal government, the "lowest bidder" is usually a small business that intentionally underbids business that we know are capable of doing the job, and a good amount of the time they've underestimated their ability to do the job - and that's the "well-intentioned" businesses. You'll have other businesses that underbid just because they want the money, not giving a damn they don't have the ability to do the job. And, because they're the lowest bidder, the government is almost always obligated to go with them due to "getting the best deal for the taxpayer money". What the government doesn't always get is the lowest bidder generally isn't always the best deal.

And the voters that have pushed this way don't understand that, either.
Dealing with some of those folks, nobody ever gets that the extra maintenance and repair that results from going too cheap costs more very quickly.

 

[jdoggivjc]

And the voters that have pushed this way don't understand that, either.
Dealing with some of those folks, nobody ever gets that the extra maintenance and repair that results from going too cheap costs more very quickly.

I probably should clarify that not every contract the government makes goes to the lowest bidder. For example, CAT I programs. Let's say for whatever reason the Army decides tomorrow it needs to replace the M1 Abrams with a new tank (not that it's happening anytime soon - after 30+ years and multiple upgrades it's still arguably the best tank in the world). The government isn't going to just let some no-name business take this contract - it'll go to a major contractor like BAE or Northrup-Grummon, subcontractors like Honeywell will handle LRUs like the turbine engines, and even government-owend facilities like Watervliet Arsenal in Albany will manufacture the cannons and the ammo plant in Scranton would manufacture the ammo.

What the government routinely screws up is the smaller items and things like contracting out publications.

 

[CycloneErik]

I probably should clarify that not every contract the government makes goes to the lowest bidder. For example, CAT I programs. Let's say for whatever reason the Army decides tomorrow it needs to replace the M1 Abrams with a new tank (not that it's happening anytime soon - after 30+ years and multiple upgrades it's still arguably the best tank in the world). The government isn't going to just let some no-name business take this contract - it'll go to a major contractor like BAE or Northrup-Grummon, subcontractors like Honeywell will handle LRUs like the turbine engines, and even government-owend facilities like Watervliet Arsenal in Albany will manufacture the cannons and the ammo plant in Scranton would manufacture the ammo.

What the government routinely screws up is the smaller items and things like contracting out publications.

That works.
Take a look at commo gear, too. Since it's not glamorous, they love to go cheap.
The old "top of the line" cell system I used to play with was cobbled together from pre-existing parts simply to save money. It was easily obsolete when fielded, but squeezed out a bunch of years.

 

[jdoggivjc]

That works.
Take a look at commo gear, too. Since it's not glamorous, they love to go cheap.
The old "top of the line" cell system I used to play with was cobbled together from pre-existing parts simply to save money. It was easily obsolete when fielded, but squeezed out a bunch of years.

Yup. I get that Windows XP is pretty much the greatest OS Microsoft has ever created. Doesn't mean weapon system's computers should still be running on it.

 

[AgronAlum]

Missouri did a huge program a couple years ago that replaced 557 bridges in a two year span. many of them are exactly as you describe: they took old, decrepit, small, rural bridges and replaced them with box culverts. I believe Pennsylvania is undergoing a similar program right now. Think of it as the "band aid" approach to fix all those little bridges around the state.

This would be preferred. It would remove the weight restrictions on those crappy bridges.

 

[NWICY]

Missouri did a huge program a couple years ago that replaced 557 bridges in a two year span. many of them are exactly as you describe: they took old, decrepit, small, rural bridges and replaced them with box culverts. I believe Pennsylvania is undergoing a similar program right now. Think of it as the "band aid" approach to fix all those little bridges around the state.

On those smaller creeks or dredge ditches isn't a box culvert as good as a bridge? The projects I've seen locally they seem to be plenty oversized. This is meant strictly as a question because I don't know boo about this subject. TIA.

 

[Die4Cy]

CBS News is running a piece about safety violations committed by Figg & MCM:

But just 10 days ago, the company was sued in South Florida by a TSA employee who was hurt at the Fort Lauderdale airport. The employee's lawyer alleges that a makeshift bridge MCM built for workers to use while the company does construction at the airport broke under his weight.

As for FIGG, a 90-ton portion of a bridge the company was assembling in Virginia in June 2012 fell apart while under construction. The Virginian Pilot reports four workers were hurt and that state regulators fined FIGG $28,000 for safety violations saying it was "pure luck no one was killed."
​

https://www.cbsnews.com/news/fiu-bridge-collapse-florida-international-university-deaths-miami/

It isn't unusual for a large company to be involved it litigation. A personal injury case is pretty run of the mill at construction companies given their line of work. I'm not sure this story means all that much.

 

[Die4Cy]

This is why I hate the speculation that comes from these kinds of articles - the writers don't understand the terms they are using, the general public doesn't understand the terms either, and conclusions get jumped to.

To be fair, this is the case withwith virtually every story you read. When you have expertise in a subject, the glaring errors are annoyingly present, but when you don't, for some reason we are prone to accept the story as it is. And the less informed the writer is, the worse it gets.

 

[throwittoblythe]

On those smaller creeks or dredge ditches isn't a box culvert as good as a bridge? The projects I've seen locally they seem to be plenty oversized. This is meant strictly as a question because I don't know boo about this subject. TIA.

You're absolutely right. Culverts are way cheaper to build than bridges. With a bridge, you need foundations, abutments, and then you put the bridge on that. With a culvert, you prep the ground, set it in place, and backfill. Super fast to build and much cheaper to maintain.

 

[Cyclonepride]

At least in terms of the Federal government, the "lowest bidder" is usually a small business that intentionally underbids business that we know are capable of doing the job, and a good amount of the time they've underestimated their ability to do the job - and that's the "well-intentioned" businesses. You'll have other businesses that underbid just because they want the money, not giving a damn they don't have the ability to do the job. And, because they're the lowest bidder, the government is almost always obligated to go with them due to "getting the best deal for the taxpayer money". What the government doesn't always get is the lowest bidder generally isn't always the best deal.

And when the impulse is to throw money at it in large stimulus-type packages, the companies that bid that type of work get really busy, and when they're busy, they either don't bid, or bid high, so the lowest bidder isn't always low at all.

 

[throwittoblythe]

And when the impulse is to throw money at it in large stimulus-type packages, the companies that bid that type of work get really busy, and when they're busy, they either don't bid, or bid high, so the lowest bidder isn't always low at all.

I often like to say "lowest price is not always the lowest cost."

 

[Acylum]

I tend to agree. The main problem isn't really the infrastructure spending. It's everything else that the State gets involved in. It just annoys me to no end that the schools/infrastructure are always the lead story in the attempts to wring more money out of us, yet they don't ever get what they need.

Another factor, explained to me by my son- in- law, who's in the state legislature, is the contractors doing the work for the state aren't idiots. Guess what happens to their bids when they see the state has raised taxes for more money for infrastructure projects. And I'm not trying to paint the contractors in a bad light. One summer I was driving the same route for about 10 weeks. There was a small bridge being replaced. Some days there was a detour, some days there was a flagman. One day I was first in line and had a chance to talk to the flagger. I asked him why are you here one day, then gone a few days, then back for a couple, then gone again. He explained that everything had to be inspected by the state at certain intervals, and sometimes the person would need to be there all day. If the state couldn't provide somebody, the contractor would have to move all their equipment to another project until somebody could show up and give them the go-ahead. That's got to be expensive. His last statement, "He has to be here all day today for example. That's him sleeping in that orange pickup over there".

 

[Cyclones_R_GR8]

Here's a link to a dashcam video from when the bridge collapsed.

http://www.miamiherald.com/news/local/community/miami-dade/article205637539.html