Pedestrian bridge collapses at FIU

[throwittoblythe]

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?

Your point is valid, though, all contractors have to meet the state requirements for quality control and inspection. It's not as if these contractors win the job and get to go build whatever they want. They still have to follow standards and specifications, whether it was in their bid or not. However, if a contractor comes in with a screaming-low bid, you can bet he's doing everything he can to build it as fast as possible while still meeting the minimum requirements.

More and more DOTs are moving to a qualifications-based selection approach. In Minnesota, where I live, they do most of their big projects through programs that select contractors based solely on their qualifications and price doesn't become a factor until after the contractor is selected.

 

[mj4cy]

Judging by what this article says "stress test" seems to be misused. It sounds like the bridge was post-tensioned. That is a common design technique where steel strands run through a structure and are tightened ("stressed") to give a structure added capacity/strength. From that article they say the strands had loosened (no mention if it was expected or not). Based on my experience, they were probably re-tensioning the cables to their design loads.

This article gives the impression they were somehow load testing the bridge above live traffic. That's unlikely, but not impossible to have occurred, and would go far beyond accepted practice.

Gosh you'd hope they didn't load test this over live traffic. I'm hoping they would have shut traffic down overnight to do it.


10 years ago I did a design/build internship for PCL Civil Constructors in Fort Lauderdale. We rehabilitated bascule span bridges over Intercoastal Waterway. You wouldn't believe how pushy Fdot is compared to back in the midwest. The contract was basically every day the bridge was done early, PCL would get $10,000 dollars. So we were working 16 hour days and lucky to get Sundays off. It was nuts. However, with incentives like that, I can see how all parties are just probably going like gang busters on projects.

However, in this case, it could have been a completely different scenario. Just don't know enough yet.

 

[Cyclonepride]

I also want to point out to those who are decrying "pushing the limits" or "going on the cheap." If these are big issues for you, you can contact your legislators about more infrastructure funding. It's a huge issue that doesn't get as much coverage as it should.

For those who live in Iowa, your state has one of the highest percentages of structurally deficient bridges relative to total inventory. The latest report out stated that 20.9% of the bridges in Iowa are structurally deficient (5,067 out of 24,215). The good news is Iowa just passed the $0.10 gas tax and now the DOT has a bunch more funding to use to improve the safety of bridges across the state.

If a story like this upsets you or brings this issue to the front of your mind, reach out to your legislators and let them know you don't want this happening in your state. It may not have prevented anything in this case, but it does highlight the need to improve our infrastructure across the board.

That figure is tossed out there a lot, but:

1. How many of these deficient bridges only serve remote rural areas with only farm traffic?
2. Why is infrastructure funding always decried when the hands are out, but never gets actually fixed?

 

[throwittoblythe]

ok, this site doesn't like the link I posted. There's a clip on CNN showing the bridge collapse...

Go to 0:41 in that link.

 

[mj4cy]

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?

The key phrase is usually "Lowest qualified bidder."

However I've noticed on small rural projects you'll get a contractor who will just lowball the bid then screw anyone and everyone over on change orders. Back when I did buildings for a consulting firm, we had to put some many cover your ass (CYA) notes and comments all over the drawings especially on public bid projects.

 

[ArgentCy]

Judging by what this article says "stress test" seems to be misused. It sounds like the bridge was post-tensioned. That is a common design technique where steel strands run through a structure and are tightened ("stressed") to give a structure added capacity/strength. From that article they say the strands had loosened (no mention if it was expected or not). Based on my experience, they were probably re-tensioning the cables to their design loads.

This article gives the impression they were somehow load testing the bridge above live traffic. That's unlikely, but not impossible to have occurred, and would go far beyond accepted practice.

I saw one video and it appeared like they put a car on top of one side and it failed right under the front of the car. That is quite the arrogance to stress test a bridge, without the main stay cables, with traffic open.

 

[throwittoblythe]

That figure is tossed out there a lot, but:

1. How many of these deficient bridges only serve remote rural areas with only farm traffic?
2. Why is infrastructure funding always decried when the hands are out, but never gets actually fixed?

Agree on both points, though I'd say to point #1: how much traffic a bridge sees doesn't change that it needs repair/replacement, but it would alter the priority. And to Point 2, I hate that this will get politicized at all. This should be a non-partisan issue. It's a shame it takes a failure like this (or the Minnesota bridge a few years back) to see real change.

 

[throwittoblythe]

You can't retention steel rods already in the concrete. I saw one video and it appeared like they put a car on top of one side and it failed right under the front of the car. That is quite the arrogance to stress test a bridge, without the main stay cables, with traffic open.

How would they have gotten a car on it? A) It's a pedestrian bridge so there may not even be room up there for a car. B) Only this span was in place, there were no approach ramps constructed. They would've had to have a big crane to lift the car into place, which is nowhere in any of the videos or photos.

 

[Cyclonepride]

Agree on both points, though I'd say to point #1: how much traffic a bridge sees doesn't change that it needs repair/replacement, but it would alter the priority. And to Point 2, I hate that this will get politicized at all. This should be a non-partisan issue. It's a shame it takes a failure like this (or the Minnesota bridge a few years back) to see real change.

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.

 

[CtownCyclone]

How would they have gotten a car on it? A) It's a pedestrian bridge so there may not even be room up there for a car. B) Only this span was in place, there were no approach ramps constructed. They would've had to have a big crane to lift the car into place, which is nowhere in any of the videos or photos.

Friendly advice: you can't win an argument with that guy, even if you have science, math, facts, etc on your side.

 

[throwittoblythe]

Gosh you'd hope they didn't load test this over live traffic. I'm hoping they would have shut traffic down overnight to do it.


10 years ago I did a design/build internship for PCL Civil Constructors in Fort Lauderdale. We rehabilitated bascule span bridges over Intercoastal Waterway. You wouldn't believe how pushy Fdot is compared to back in the midwest. The contract was basically every day the bridge was done early, PCL would get $10,000 dollars. So we were working 16 hour days and lucky to get Sundays off. It was nuts. However, with incentives like that, I can see how all parties are just probably going like gang busters on projects.

However, in this case, it could have been a completely different scenario. Just don't know enough yet.

It wouldn't be that unreasonable to PT a bridge over live traffic, right? If the PT is only needed to support the bridge under design loads, it could have been designed to be self-supporting during construction, but needed to have the PT completed before final completion and/or opening to pedestrians.

The term "load test" is misplaced here. A load test would mean they put a bunch of actuators or other devices on the bridge to replicate the design loads. Testing the PT to ensure it's meeting the design loads would be different than load testing the bridge.

 

[mj4cy]

It wouldn't be that unreasonable to PT a bridge over live traffic, right? If the PT is only needed to support the bridge under design loads, it could have been designed to be self-supporting during construction, but needed to have the PT completed before final completion and/or opening to pedestrians.

The term "load test" is misplaced here. A load test would mean they put a bunch of actuators or other devices on the bridge to replicate the design loads. Testing the PT to ensure it's meeting the design loads would be different than load testing the bridge.

Agreed. I have little experience with bridges (other than formwork design) as well as PT, so good insight.

 

[throwittoblythe]

Agreed. I have little experience with bridges (other than formwork design) as well as PT, so good insight.

I was honestly asking. I know you're a structural engineer and we both studied under the great Wayne Klaiber at ISU.

 

[mj4cy]

I was honestly asking. I know you're a structural engineer and we both studied under the great Wayne Klaiber at ISU.

Ah! Missed your question. From the pictures I saw during construction they had temporary supports presumably present until the bridge can support itself. My guess is it would be okay.

However, I think the bigger picture is barring a huge oversight, I would think every single construction phase and sequence has been thought out in terms of temporary support and traffic considerations. Again, doesn't mean there wasn't a miscommunication or oversight.

Sounds bad as I know lives were lost, but I'll be interested to see what the specific causes were in this case.

 

[cowgirl836]

I also want to point out to those who are decrying "pushing the limits" or "going on the cheap." If these are big issues for you, you can contact your legislators about more infrastructure funding. It's a huge issue that doesn't get as much coverage as it should.

For those who live in Iowa, your state has one of the highest percentages of structurally deficient bridges relative to total inventory. The latest report out stated that 20.9% of the bridges in Iowa are structurally deficient (5,067 out of 24,215). The good news is Iowa just passed the $0.10 gas tax and now the DOT has a bunch more funding to use to improve the safety of bridges across the state.

If a story like this upsets you or brings this issue to the front of your mind, reach out to your legislators and let them know you don't want this happening in your state. It may not have prevented anything in this case, but it does highlight the need to improve our infrastructure across the board.

I've seen what the numbers are for WI and it only gets worse every year as funding continues to dry up. Guess I'm glad I at least don't go over any bridges in my daily commute.

 

[throwittoblythe]

Ah! Missed your question. From the pictures I saw during construction they had temporary supports presumably present until the bridge can support itself. My guess is it would be okay.

However, I think the bigger picture is barring a huge oversight, I would think every single construction phase and sequence has been thought out in terms of temporary support and traffic considerations. Again, doesn't mean there wasn't a miscommunication or oversight.

Sounds bad as I know lives were lost, but I'll be interested to see what the specific causes were in this case.

Yeah, I can't get over the fact that the bridge failed without any load on it, so it wasn't even strong enough to support it's own weight. The fact that it sat for almost a week before it failed, leads me to believe something sudden happened. Structures like that aren't prone to a slow, gradual (ductile) failure. It would've had lots of signs of issues if it was slowly failing. That's not to say they could've been overlooked.

If they were actually tensioning the bridge when it collapsed, it's possible they over-tensioned the bridge and caused it to crack. Or, it's possible the PT strands were not at a high enough tension to support it's self-weight. Or, maybe one of the tendons slipped and lost all its load causing a sharp reduction in capacity. Hard to say until we get the full story.

 

[throwittoblythe]

I've seen what the numbers are for WI and it only gets worse every year as funding continues to dry up. Guess I'm glad I at least don't go over any bridges in my daily commute.

Wisconsin is doing surprisingly well compared to many. You guys were "only" at 8.9% of bridges rated as structurally deficient which is right about average across the country.

 

[ArgentCy]

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

 

[CtownCyclone]

That figure is tossed out there a lot, but:

1. How many of these deficient bridges only serve remote rural areas with only farm traffic?
2. Why is infrastructure funding always decried when the hands are out, but never gets actually fixed?

https://www.artbabridgereport.org/state-profile/IA.html

They break out road usage types on that link.

 

[ArgentCy]

How would they have gotten a car on it? A) It's a pedestrian bridge so there may not even be room up there for a car. B) Only this span was in place, there were no approach ramps constructed. They would've had to have a big crane to lift the car into place, which is nowhere in any of the videos or photos.

Watch that CNN video and pause at 48 seconds. Tell me that isn't a white car/SUV that falls down. That is the same event I saw but the video was from a different angle and better quality.

I have no idea why you'd stress test with a car. That does seem strange but look at their results.