3 ms·

I've seen this stated "Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands."

hn_throwaway_99 2y ago
In modern days we generally stand in awe of ancient structures that have stood for millennia. But in some sense, many ancient engineers had to drastically overbuild their bridges and other structures because they didn't have the tools to know what the "barely stands" threshold was, so they had to build for a big margin of error when they lacked the tools of precision.
- erik_seaberg 2y ago
  Yeah, imagine digging up red clay, throwing it in a charcoal furnace, and then hammering it for a while. You can tell you're getting wrought iron, but would you know from one batch to the next whether it's good?
  - j16sdiz 2y ago
    They did that with specification like "use red clay from this village" with "charcoal from that city" in this furnace. It is not scalable, but the quality is quite stable across batches
    - fmajid 2y ago
      And then you have the rebar-free Roman lime-pozzolan concrete used in the Pantheon, still standing after 2000 years.
      - lesuorac 2y ago
        Not a civil engineer but it sounds like the Romans knew much better then "baked red clay strong". > https://en.wikipedia.org/wiki/Pantheon,_Rome#Structure https://en.wikipedia.org/wiki/Pantheon,_Rome#Structure > The stresses in the dome were found to be substantially reduced by the use of successively less dense aggregate stones, such as small pots or pieces of pumice, in higher layers of the dome. Mark and Hutchison estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater. Hidden chambers engineered within the rotunda form a sophisticated structural system.[55] This reduced the weight of the roof, as did the oculus eliminating the apex. That said, I'm guessing the Pantheon is in one piece (unlike the coliseum) because it's been used as a church for the past ~1600 years and presumably (similar to Notre Dame) it gets repair as-needed.
- bluGill 2y ago
  Most of those old bridges are not suitable for modern needs. They are nice to look at, but cannot carry a truck, or can only at very low speeds. Or buildings without restrooms. Just adding light to old things often destroys the beauty people praise them for
kazinator 2y ago
In reality, it's more like: any idiot can build a bridge that, in some places, is 5X as strong as it will ever need to be, in other places 2X as strong, and in a couple places only 0.8X as strong as it will ever need to be. It takes the engineer to build it so that every part is 1.25X as strong as it will ever need to be, consistently everywhere. To the idiot, that then looks like it is barely standing, because some parts are 4X weaker than he would have made them, based on bad intutition.
armchairhacker 2y ago
On the other hand, in many cases what's defined as the "bare minimum" ends up being more than expected. The corner-cutting approach ends up pricier than the thorough approach in the long run, because it must be constantly adjusted if not entirely re-done. e.g. building a bridge to support a city's normal traffic density, but the city ends up growing, and the way the bridge was designed makes adding reinforcement difficult. Or building a bridge whose materials start to melt at a certain temperature that's above what's expected for the region, but climate change raises the temperature over the threshold, so it needs a completely different material. Hence the article's point that software companies should invest in formal methods, because while formally proving something is a long process without much reward in the short term, it eliminates an entire class of bugs which, in some long-term projects, makes it worth the effort.
- vlovich123 2y ago
  Conversely, we also know that taking longer to build something scalable is more expensive than just building cheaper things that accomplish the job now and solving the bigger problems when they’re relevant to the point where it can be the tipping point of success in the first place. In other words, that super reliable bridge that can handle all the growth you throw at it can take longer and too much money and result in a city that fails to have a growth problem in the first place. We know that’s true experientially in both CS (YAGNI) and in the physical spaces (eg Wright brothers constantly iterating with cheap prototypes until they figured out something that worked and SpaceX doing similar things with their prototypes). Iteration = learning. In theory formal methods let you iterate at a cheaper phase of the project. In practice, the methods themselves are very difficult to scale to large projects and these days require you to build the project twice - once for the formal language and then hand-translated to a production language.

hn_throwaway_99 2y ago

In modern days we generally stand in awe of ancient structures that have stood for millennia. But in some sense, many ancient engineers had to drastically overbuild their bridges and other structures because they didn't have the tools to know what the "barely stands" threshold was, so they had to build for a big margin of error when they lacked the tools of precision.

erik_seaberg 2y ago
Yeah, imagine digging up red clay, throwing it in a charcoal furnace, and then hammering it for a while. You can tell you're getting wrought iron, but would you know from one batch to the next whether it's good?
- j16sdiz 2y ago
  They did that with specification like "use red clay from this village" with "charcoal from that city" in this furnace. It is not scalable, but the quality is quite stable across batches
  - fmajid 2y ago
    And then you have the rebar-free Roman lime-pozzolan concrete used in the Pantheon, still standing after 2000 years.
    - lesuorac 2y ago
      Not a civil engineer but it sounds like the Romans knew much better then "baked red clay strong". > https://en.wikipedia.org/wiki/Pantheon,_Rome#Structure https://en.wikipedia.org/wiki/Pantheon,_Rome#Structure > The stresses in the dome were found to be substantially reduced by the use of successively less dense aggregate stones, such as small pots or pieces of pumice, in higher layers of the dome. Mark and Hutchison estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater. Hidden chambers engineered within the rotunda form a sophisticated structural system.[55] This reduced the weight of the roof, as did the oculus eliminating the apex. That said, I'm guessing the Pantheon is in one piece (unlike the coliseum) because it's been used as a church for the past ~1600 years and presumably (similar to Notre Dame) it gets repair as-needed.
bluGill 2y ago
Most of those old bridges are not suitable for modern needs. They are nice to look at, but cannot carry a truck, or can only at very low speeds. Or buildings without restrooms. Just adding light to old things often destroys the beauty people praise them for

kazinator 2y ago

In reality, it's more like: any idiot can build a bridge that, in some places, is 5X as strong as it will ever need to be, in other places 2X as strong, and in a couple places only 0.8X as strong as it will ever need to be. It takes the engineer to build it so that every part is 1.25X as strong as it will ever need to be, consistently everywhere. To the idiot, that then looks like it is barely standing, because some parts are 4X weaker than he would have made them, based on bad intutition.

armchairhacker 2y ago

On the other hand, in many cases what's defined as the "bare minimum" ends up being more than expected. The corner-cutting approach ends up pricier than the thorough approach in the long run, because it must be constantly adjusted if not entirely re-done. e.g. building a bridge to support a city's normal traffic density, but the city ends up growing, and the way the bridge was designed makes adding reinforcement difficult. Or building a bridge whose materials start to melt at a certain temperature that's above what's expected for the region, but climate change raises the temperature over the threshold, so it needs a completely different material. Hence the article's point that software companies should invest in formal methods, because while formally proving something is a long process without much reward in the short term, it eliminates an entire class of bugs which, in some long-term projects, makes it worth the effort.

vlovich123 2y ago
Conversely, we also know that taking longer to build something scalable is more expensive than just building cheaper things that accomplish the job now and solving the bigger problems when they’re relevant to the point where it can be the tipping point of success in the first place. In other words, that super reliable bridge that can handle all the growth you throw at it can take longer and too much money and result in a city that fails to have a growth problem in the first place. We know that’s true experientially in both CS (YAGNI) and in the physical spaces (eg Wright brothers constantly iterating with cheap prototypes until they figured out something that worked and SpaceX doing similar things with their prototypes). Iteration = learning. In theory formal methods let you iterate at a cheaper phase of the project. In practice, the methods themselves are very difficult to scale to large projects and these days require you to build the project twice - once for the formal language and then hand-translated to a production language.