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At the risk of seeming callous, I am not convinced it is obvious that bridges should never collapse. This is an unreachable goal that will just make bridges mo

At the risk of seeming callous, I am not convinced it is obvious that bridges should never collapse. This is an unreachable goal that will just make bridges more expensive and create excessive regulation. No artifact of man is 100% reliable, the only rational goal is a certain number of "nines." The users of a system should decide how many nines they are willing to pay for. For me personally, A bridge with a 99.9% chance of not collapsing in a given year is good enough.

deleted 5y ago
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dijit 5y ago
Nobody is advocating for object permanence. People advocate for understood constraints of critical infrastructure. Engineers usually have knowledge about longevity and reliability of components. There are examples of man-made systems which absolutely require 100% reliability, but those still have lifetimes and will be destroyed at some point to be replaced with something else[0]. A bridge can be destroyed, but it should not collapse without prior warning. [0]: https://www.youtube.com/watch?v=eY-XHAoVEeU https://www.youtube.com/watch?v=eY-XHAoVEeU
- omnicognate 5y ago
  > Nobody is advocating for object permanence. I am. People need to understand that bridges continue to exist when they're not looking at them. (Edit: https://en.m.wikipedia.org/wiki/Object_permanence https://en.m.wikipedia.org/wiki/Object_permanence)
  - mprovost 5y ago
- opwieurposiu 5y ago
  Did you watch this video? Tom claims in the video that the barrier is designed for up to a thousand year tide. That's essentially the same as the three nines standard I advocated.
- throw10920 5y ago
  100% reliability is physically impossible. "reliability" is defined to include resistance to abnormal situations. A bridge might be 100% reliable when winds don't exceed 100mph...an event that might have a 1% probability per year in its area of construction, which is clearly highly unlikely, but still something that is accounted for in reliability, uptime, and failure rate metrics. I don't even know if you can achieve 100% reliability given a set of plausible situations/usage, because you'd have to imagine every single possible failure mode for the thing that you're building. That is - the threat of "destruction" proper (which you contrasted with "collapse without prior warning") is included in the reliability metrics for a device. The point stands. Nothing that humans build can be 100% reliable - the only thing you can do is asymptotically approach it. Now, that said - three nines per year is way too low for me, personally. Five nines is more comfortable (and if it's cheap I'd like to go higher).
lkxijlewlf 5y ago
> At the risk of seeming callous, I am not convinced it is obvious that bridges should never collapse. Nobody is saying that a bridge should last forever. They're saying repair it as long as you can, then replace the bridge so that a collapse never happens.
rvs-ie 5y ago
> For me personally, A bridge with a 99.9% chance of not collapsing in a given year is good enough. So you are ok if in a city with 100 bridges there is an average of one collapse every 10 years?
- opwieurposiu 5y ago
  Yes one bridge collapse a decade would be acceptable to me provided it keeps the cost down. Other people may be willing to pay for more nines, the point is that infinity nines costs infinity dollars.
  - syki 5y ago
    You are ok with a bridge collapse every 10 years? Do you understand how rare bridge collapses are today and that this would be a massive increase in the rate of failure?
    - throw10920 5y ago
      They were just giving their personal comfort threshold. I mean, technically, one would need to look at the reliability-cost curve. opwieurposiu would almost certainly be fine with eight 9's of reliability if it only cost twice as much as three 9's. The fact that they have a really high risk tolerance in this area don't really undermine their general point.
      - syki 5y ago
        If a person’s risk tolerance on something is out of whack of what almost everyone else is comfortable with then there is a problem with that position. At least as it pertains to public policy. I’ll rephrase and say that I hope OP is not in a position to have his/her views in this area become policy.
  - tagoregrtst 5y ago
    Pittsburgh has well over 200 bridges. It’d be a failure every 5 years. Ill stick to our current failure rate, thank you. IT “reliability” rates isn't that impressive in other fields of engineering.
cogman10 5y ago
A rope bridge with wood planks will last as long as someone maintains the rope and the planks. Nobody is advocating that "the perfect bridge" be built. They are advocating that already built bridges receive regular maintenance. Expecting that a bridge doesn't collapse is an entirely achievable goal. Expecting that a bridge doesn't collapse without maintenance is very unlikely.

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dijit 5y ago

Nobody is advocating for object permanence. People advocate for understood constraints of critical infrastructure. Engineers usually have knowledge about longevity and reliability of components. There are examples of man-made systems which absolutely require 100% reliability, but those still have lifetimes and will be destroyed at some point to be replaced with something else[0]. A bridge can be destroyed, but it should not collapse without prior warning. [0]: https://www.youtube.com/watch?v=eY-XHAoVEeU https://www.youtube.com/watch?v=eY-XHAoVEeU

omnicognate 5y ago
> Nobody is advocating for object permanence. I am. People need to understand that bridges continue to exist when they're not looking at them. (Edit: https://en.m.wikipedia.org/wiki/Object_permanence https://en.m.wikipedia.org/wiki/Object_permanence)
- mprovost 5y ago
opwieurposiu 5y ago
Did you watch this video? Tom claims in the video that the barrier is designed for up to a thousand year tide. That's essentially the same as the three nines standard I advocated.
throw10920 5y ago
100% reliability is physically impossible. "reliability" is defined to include resistance to abnormal situations. A bridge might be 100% reliable when winds don't exceed 100mph...an event that might have a 1% probability per year in its area of construction, which is clearly highly unlikely, but still something that is accounted for in reliability, uptime, and failure rate metrics. I don't even know if you can achieve 100% reliability given a set of plausible situations/usage, because you'd have to imagine every single possible failure mode for the thing that you're building. That is - the threat of "destruction" proper (which you contrasted with "collapse without prior warning") is included in the reliability metrics for a device. The point stands. Nothing that humans build can be 100% reliable - the only thing you can do is asymptotically approach it. Now, that said - three nines per year is way too low for me, personally. Five nines is more comfortable (and if it's cheap I'd like to go higher).

lkxijlewlf 5y ago

> At the risk of seeming callous, I am not convinced it is obvious that bridges should never collapse. Nobody is saying that a bridge should last forever. They're saying repair it as long as you can, then replace the bridge so that a collapse never happens.

rvs-ie 5y ago

> For me personally, A bridge with a 99.9% chance of not collapsing in a given year is good enough. So you are ok if in a city with 100 bridges there is an average of one collapse every 10 years?

opwieurposiu 5y ago
Yes one bridge collapse a decade would be acceptable to me provided it keeps the cost down. Other people may be willing to pay for more nines, the point is that infinity nines costs infinity dollars.
- syki 5y ago
  You are ok with a bridge collapse every 10 years? Do you understand how rare bridge collapses are today and that this would be a massive increase in the rate of failure?
  - throw10920 5y ago
    They were just giving their personal comfort threshold. I mean, technically, one would need to look at the reliability-cost curve. opwieurposiu would almost certainly be fine with eight 9's of reliability if it only cost twice as much as three 9's. The fact that they have a really high risk tolerance in this area don't really undermine their general point.
    - syki 5y ago
      If a person’s risk tolerance on something is out of whack of what almost everyone else is comfortable with then there is a problem with that position. At least as it pertains to public policy. I’ll rephrase and say that I hope OP is not in a position to have his/her views in this area become policy.
- tagoregrtst 5y ago
  Pittsburgh has well over 200 bridges. It’d be a failure every 5 years. Ill stick to our current failure rate, thank you. IT “reliability” rates isn't that impressive in other fields of engineering.

cogman10 5y ago

A rope bridge with wood planks will last as long as someone maintains the rope and the planks. Nobody is advocating that "the perfect bridge" be built. They are advocating that already built bridges receive regular maintenance. Expecting that a bridge doesn't collapse is an entirely achievable goal. Expecting that a bridge doesn't collapse without maintenance is very unlikely.