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> Plenty of poorly designed steel bridges from the 19th century have collapsed as well That's true. But I only meant that particular bridge, which did last for

by rdtsc 3y ago

> Plenty of poorly designed steel bridges from the 19th century have collapsed as well That's true. But I only meant that particular bridge, which did last for 100+ years. So, when the architects and the engineers go to the archives to relearn a few things, they can focus on the ones which haven't collapsed.

hellofellows 3y ago
+ why even remove the steel bridge in the first place?
- speedgoose 3y ago
  You have more pictures on the Norwegian Wikipedia page: https://no.m.wikipedia.org/wiki/Tretten_bru#/media/Fil%3ATretten_bro_(1895).jpg https://no.m.wikipedia.org/wiki/Tretten_bru#/media/Fil%3ATre... The old one wasn’t wide while the new one had two lanes and a normal sized sidewalk.
- TylerE 3y ago
  Moisture causes corrosion. Rivers produce lots of moisture. Corrosion weakens the steel. It's literally the metal flaking away. All steel corrodes. Even stainless. Once corrosion sets in and the outside of the metal starts to pit, the corrosion speeds up drastically. (The old area vs volume thing, same thing that makes lump coal difficult to ignite while aerosolized coal dust is practically an explosive). Here's a modern US bridge - all steel - that collapsed in Pittsburgh two years ago. In some areas over 80% of the original steel thinkness was gone after 49 years. https://www.youtube.com/watch?v=J-VnWB4fiFk https://www.youtube.com/watch?v=J-VnWB4fiFk
  - Gare 3y ago
    Paint protects steel. A frequently painted steel bridge can last centuries. As always, lack of maintenance and poor design choices (use of corten steel) are the culprit.
    - TylerE 3y ago
      Something like 20% of the bridges in this country are 10 years or more past their design lifetime and mostly not due to be replaced any time soon. You think they're keeping on top of painting every one? Saying preventing corrosion is as easy as slapping on paint is like saying computer security is as easy as not leaking your password. There are a million things that could happen, many of which are outside what any single person could control.
      - Gare 3y ago
        I don't know in what poor country you live, but in my country bridges are well maintained and I don't recall a single critical failure. Even though we're one of the poorest EU countries.
        tharkun__ 3y ago
        I don't know in what rich poor EU country you live, but in my "rich country" bridges are basically left to their own devices until a critical problem occurs and then they hastily start repairing it. In some cases they've been repairing bridges for decades that way. Some have recently finally actually been replaced or are being replaced. But nobody is going out and replacing a bridge that isn't on the brink of collapse and held up by "essentially duct tape".
        TylerE 3y ago
        https://infrastructurereportcard.org/cat-item/bridges-infrastructure/ https://infrastructurereportcard.org/cat-item/bridges-infras... "There are more than 617,000 bridges across the United States. Currently, 42% of all bridges are at least 50 years old, and 46,154, or 7.5% of the nation’s bridges, are considered structurally deficient, meaning they are in “poor” condition. Unfortunately, 178 million trips are taken across these structurally deficient bridges every day. In recent years, though, as the average age of America’s bridges increases to 44 years, the number of structurally deficient bridges has continued to decline; however, the rate of improvements has slowed. A recent estimate for the nation’s backlog of bridge repair needs is $125 billion. We need to increase spending on bridge rehabilitation from $14.4 billion annually to $22.7 billion annually, or by 58%, if we are to improve the condition. At the current rate of investment, it will take until 2071 to make all of the repairs that are currently necessary, and the additional deterioration over the next 50 years will become overwhelming."
  - arp242 3y ago
    There are metal bridges over 100 years old still in service today, including a few you've heard of. Do you know this specific bridge was replaced for this specific reason, or are you just making stuff up?
    - TylerE 3y ago
      I’m not making any thing up. Why the hostile tone? This is basic materials engineering.
      - arp242 3y ago
        The question was why this specific steel bridge was replaced. Not "what are possible reasons someone could replace steel bridges?" and it's absolutely not "basic materials engineering" that every bridge needs replacing after a fixed amount of time due to corrosion. So again, do you know this specific bridge was replaced for this specific reason, or are you just making stuff up? Because bumping in on a specific question with a generic answer without any knowledge if that applies to this specific case is making stuff up. The hostile tone is because you're talking complete nonsense with great arrogance.
x3n0ph3n3 3y ago
To be fair, there have been a lot of advancements in timber and glue -- They just didn't take into account their weaknesses when designing (e.g. Stress that would pull laminated beams apart).
- Gare 3y ago
  There are always unknown unknowns in trying new designs and/or materials. Even with all the simulations and calculations, nothing beats experience. Sure, novel things should be tried, but in a conservative manner. Overdesign first, then optimize iteratively. Because failure costs lives.
  - mcphage 3y ago
    Glulam isn’t a new material, it’s over 100 years old.
    - Gare 3y ago
      How many 70 m span glulam road bridges have been built in those 100 years?
      - ikekkdcjkfke 3y ago
        Yeah, exposing load bearing wood and glue to the elements requires some extra caution and engineering intuition
  - ikekkdcjkfke 3y ago
    I believe the failure happened in the joint between the wood and steel. The joint was a sandwich with very thin slices and with many nails. Anyone with materials intuition knows that puncturing a material to such a degree weakens it. Mix in constant moisture and single points of failure.. Should have been a couple of big old bolts and some bracings, alternately thicker slices in the sandwich
ajross 3y ago
Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? Bridges on the whole are pretty clearly better built and safer today then they were 130 years ago. I don't think there's any significant argument to the contrary. There are outliers in both directions, obviously. The old one at this site looks like it was pretty great. The new one sucked. That doesn't say much about why that was true, just that it was.
- rdtsc 3y ago
  > Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? For sure, we can each talk about different things. I can talk about ironic things and you can talk about statistics, and we can still be friends! > That doesn't say much about why that was true, just that it was. Well, why do you think it sucked?
- mannykannot 3y ago
  > Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? And why not? In this particular case, the statistics did not justify the expectation that this bridge would be at least as robust as the one it replaced. There's a general point to be made about engineering progress, but here we have a case which bucks the trend. Speaking in generalities when the topic is a specific incident is a way of missing the point.
- Aeolun 3y ago
  On the whole they may be better built, but the same design in steel would likely not have failed? I guess that’s what they’re going for when they say aesthetics had too much of a focus?
  - ajross 3y ago
    > On the whole they may be better built, but the same design in steel would likely not have failed? I don't see how that follows? Lots of steel bridges have failed over the past 130 years. The overwhelming majority of new-built bridges or any material don't fail. People really, really want this to be about "aesthetics" because it confirms their priors about being smarter than the rest of the world or whatever. I'm just saying that's 100% bunk and that there's zero evidence for that hypothesis. Architecture has had a "strong focus on aesthetics" since the very first stones were piled up to make a temple. Let's not get ahead of ourselves here.

by rdtsc 3y ago

hellofellows 3y ago

+ why even remove the steel bridge in the first place?

speedgoose 3y ago
You have more pictures on the Norwegian Wikipedia page: https://no.m.wikipedia.org/wiki/Tretten_bru#/media/Fil%3ATretten_bro_(1895).jpg https://no.m.wikipedia.org/wiki/Tretten_bru#/media/Fil%3ATre... The old one wasn’t wide while the new one had two lanes and a normal sized sidewalk.
TylerE 3y ago
Moisture causes corrosion. Rivers produce lots of moisture. Corrosion weakens the steel. It's literally the metal flaking away. All steel corrodes. Even stainless. Once corrosion sets in and the outside of the metal starts to pit, the corrosion speeds up drastically. (The old area vs volume thing, same thing that makes lump coal difficult to ignite while aerosolized coal dust is practically an explosive). Here's a modern US bridge - all steel - that collapsed in Pittsburgh two years ago. In some areas over 80% of the original steel thinkness was gone after 49 years. https://www.youtube.com/watch?v=J-VnWB4fiFk https://www.youtube.com/watch?v=J-VnWB4fiFk
- Gare 3y ago
  Paint protects steel. A frequently painted steel bridge can last centuries. As always, lack of maintenance and poor design choices (use of corten steel) are the culprit.
  - TylerE 3y ago
    Something like 20% of the bridges in this country are 10 years or more past their design lifetime and mostly not due to be replaced any time soon. You think they're keeping on top of painting every one? Saying preventing corrosion is as easy as slapping on paint is like saying computer security is as easy as not leaking your password. There are a million things that could happen, many of which are outside what any single person could control.
    - Gare 3y ago
      I don't know in what poor country you live, but in my country bridges are well maintained and I don't recall a single critical failure. Even though we're one of the poorest EU countries.
      - tharkun__ 3y ago
        I don't know in what rich poor EU country you live, but in my "rich country" bridges are basically left to their own devices until a critical problem occurs and then they hastily start repairing it. In some cases they've been repairing bridges for decades that way. Some have recently finally actually been replaced or are being replaced. But nobody is going out and replacing a bridge that isn't on the brink of collapse and held up by "essentially duct tape".
      - TylerE 3y ago
        https://infrastructurereportcard.org/cat-item/bridges-infrastructure/ https://infrastructurereportcard.org/cat-item/bridges-infras... "There are more than 617,000 bridges across the United States. Currently, 42% of all bridges are at least 50 years old, and 46,154, or 7.5% of the nation’s bridges, are considered structurally deficient, meaning they are in “poor” condition. Unfortunately, 178 million trips are taken across these structurally deficient bridges every day. In recent years, though, as the average age of America’s bridges increases to 44 years, the number of structurally deficient bridges has continued to decline; however, the rate of improvements has slowed. A recent estimate for the nation’s backlog of bridge repair needs is $125 billion. We need to increase spending on bridge rehabilitation from $14.4 billion annually to $22.7 billion annually, or by 58%, if we are to improve the condition. At the current rate of investment, it will take until 2071 to make all of the repairs that are currently necessary, and the additional deterioration over the next 50 years will become overwhelming."
- arp242 3y ago
  There are metal bridges over 100 years old still in service today, including a few you've heard of. Do you know this specific bridge was replaced for this specific reason, or are you just making stuff up?
  - TylerE 3y ago
    I’m not making any thing up. Why the hostile tone? This is basic materials engineering.
    - arp242 3y ago
      The question was why this specific steel bridge was replaced. Not "what are possible reasons someone could replace steel bridges?" and it's absolutely not "basic materials engineering" that every bridge needs replacing after a fixed amount of time due to corrosion. So again, do you know this specific bridge was replaced for this specific reason, or are you just making stuff up? Because bumping in on a specific question with a generic answer without any knowledge if that applies to this specific case is making stuff up. The hostile tone is because you're talking complete nonsense with great arrogance.

x3n0ph3n3 3y ago

To be fair, there have been a lot of advancements in timber and glue -- They just didn't take into account their weaknesses when designing (e.g. Stress that would pull laminated beams apart).

Gare 3y ago
There are always unknown unknowns in trying new designs and/or materials. Even with all the simulations and calculations, nothing beats experience. Sure, novel things should be tried, but in a conservative manner. Overdesign first, then optimize iteratively. Because failure costs lives.
- mcphage 3y ago
  Glulam isn’t a new material, it’s over 100 years old.
  - Gare 3y ago
    How many 70 m span glulam road bridges have been built in those 100 years?
    - ikekkdcjkfke 3y ago
      Yeah, exposing load bearing wood and glue to the elements requires some extra caution and engineering intuition
- ikekkdcjkfke 3y ago
  I believe the failure happened in the joint between the wood and steel. The joint was a sandwich with very thin slices and with many nails. Anyone with materials intuition knows that puncturing a material to such a degree weakens it. Mix in constant moisture and single points of failure.. Should have been a couple of big old bolts and some bracings, alternately thicker slices in the sandwich

ajross 3y ago

Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? Bridges on the whole are pretty clearly better built and safer today then they were 130 years ago. I don't think there's any significant argument to the contrary. There are outliers in both directions, obviously. The old one at this site looks like it was pretty great. The new one sucked. That doesn't say much about why that was true, just that it was.

rdtsc 3y ago
> Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? For sure, we can each talk about different things. I can talk about ironic things and you can talk about statistics, and we can still be friends! > That doesn't say much about why that was true, just that it was. Well, why do you think it sucked?
mannykannot 3y ago
> Isn't that basically arguing "Don't talk to me about statistics, I want to talk about this one specific data point"? And why not? In this particular case, the statistics did not justify the expectation that this bridge would be at least as robust as the one it replaced. There's a general point to be made about engineering progress, but here we have a case which bucks the trend. Speaking in generalities when the topic is a specific incident is a way of missing the point.
Aeolun 3y ago
On the whole they may be better built, but the same design in steel would likely not have failed? I guess that’s what they’re going for when they say aesthetics had too much of a focus?
- ajross 3y ago
  > On the whole they may be better built, but the same design in steel would likely not have failed? I don't see how that follows? Lots of steel bridges have failed over the past 130 years. The overwhelming majority of new-built bridges or any material don't fail. People really, really want this to be about "aesthetics" because it confirms their priors about being smarter than the rest of the world or whatever. I'm just saying that's 100% bunk and that there's zero evidence for that hypothesis. Architecture has had a "strong focus on aesthetics" since the very first stones were piled up to make a temple. Let's not get ahead of ourselves here.