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Comment by irjustin | Hacker News Reader

This situation is terrible, but to your specific question:

Anyone can build a bridge, but it takes an engineer to barely make it stand.

I like this quote. We have a medieval bridge near to our house (1000 years old perhaps), it's incredibly solidly built, but could you call it well-engineered?

It's a subtle distinction that I don't think many in the digital realm quite grasp either i.e. far too many over-engineered technical solutions for features and products that aren't even desired

"but could you call it well-engineered"

If it is still standing after 1000 years, I would say yes. You cannot build a bridge out of stones with bad engineering - it would collapse under its own weight.

edit: does "well engineered" now means over engineered to some?

"If it is still standing after 1000 years, I would say yes" but what if they included far more material in areas where it wasn't needed, skimped on other areas and it fell down tomorrow? It's almost a philosophical question, and it's true that the bridge builders happened across a solid design by accident.

But I think the true definition of engineering has to encompass a level of efficiency through design, calculation and rationalization. In other words, echoing what the original commenter said, including only what is barely necessary.

"and it's true that the bridge builders happened across a solid design by accident"

Or by experience and learning from other sucessful bridges? Stone bridges were not new in the year 1000.

There is a roman bridge that was allmost completely surviving all this time, till it was blown up in WW2:

https://en.m.wikipedia.org/wiki/Ponte_Pietra_(Verona)

If they wanted a cheap solution, they would have used wood. But wood does not last a 1000 years.

Personally I salute anyone, who can build something that lasts that long.

"including only what is barely necessary."

And "barely necessary" in solid engineering includes lots of safety margins. Not barely standing.

And yes, that includes not using more than you need, because the more material you use, the heavier your bridge is -> the greater are the forces on the structure itself even with no one passing over it.

There are some fun games out there on various plattforms, google "bridge builder"

Not a scientific simulation of course, but they do show the concept.

> But I think the true definition of engineering has to encompass a level of efficiency through design, calculation and rationalization.

The 1000 year medieval bridge we're talking about could have been an efficient design for its time.

When you'd be expected to stand under it while the local army/militia marched over it, incentives tended to align quite handily.

> only what is barely necessary.

But then one must make clear: necessary for what.

> and it's true that the bridge builders happened across a solid design by accident.

I think there is a great overlap between "holds for whatever scheme the prefecture will do to test it while I stand under" and "holds for a thousand years".

There is like a limit where fatigue stress stops being a thing in a cycle graph. Many failure modes is due to penny wise cost cutting.

I like to tell people that all engineering is about tradeoffs.

People who engineered bridges during Roman Empire had different tradeoffs to consider than people who were building bridges in 20th century.

Standing for a thousand years is rarely an ultimate goal when engineering a bridge although it is possible that Romans planned for longer timescales than us.

If we decided to build like Romans did, there would likely be very little infrastructure and many structures would simply be impossible to construct.

"If we decided to build like Romans did, there would likely be very little infrastructure"

Why? The romans build lots of infrastructure. Roads, sewage, irrigation, .. and they used the materials and technics of their time.

Can't we really do better today, with all our advanced technology?

Or can't we, because everything has to be cheap, cheap, cheap?

I mean, the romans used slaves. That is cheap. But we have machines.

How much population did the Romans build for? How much weight were the Romans subjecting their structures to, and at what acceleration/deceleration?

Do you know the movements of the supply and demand curves of the materials required since Roman times?

These types of hypotheticals are a waste of time, and only serve to illustrate hubris, as if something as complicated as comparing Roman construction and resources to modern day construction and resources could be possible.

"as if something as complicated as comparing Roman construction and resources to modern day construction and resources could be possible."

Well, one can compare the results.

Personally I like things that are build solid and can last a 1000 years.

But I don't think I said the romans build better. They just had a different intention: long lasting.

> Can't we really do better today, with all our advanced technology?

You implied a whole host of things with this statement, and considering the topic of this thread, also ramming a Roman bridge with a fully loaded modern day cargo ship.

The point is there are so many moving parameters, it is nonsensical to take 1 result of 1 technique from 1 point of time and use that as a basis for what one can expect at other points in time.

Erm, that was just directed at this point, which I quoted:

"If we decided to build like Romans did, there would likely be very little infrastructure"

The bridge has lasted a thousand years because nobody is driving 18-wheelers over it. It has nothing to do with the intentions of the builder.

"It has nothing to do with the intentions of the builder"

Why not? They did not have the intention to make the bridge resistant to such heavy loads, as that was not a use case at that time.

They had the intention to make a bridge to last as long as possible for the traffic at their time. And they surely succeded with this.

Now whether they also could have made a bridge that resists 18 wheelers for 1000 years, well, I don't know.

This is survivorship bias in action. They intended to build a bridge. That is all we can infer from the fact that a bridge exists. That they used available materials and the bridge was not abused by subsequent usage outside its design spec is not proof of any specific intention on the part of the builder. That exists only in your head. It's like assuming dinosaurs died in specific spots with the intent that their bones petrify and fossilize. You're reading too much into not enough facts.

Maybe, but lots of roman buildings endured the time in much better shape, than many buildings that were build after them. Have you seen some of them in front of you? I have and I am impressed. (I am in italy right now to go look at some more).

Also we know a bit more about the romans than just their bridges.

You can't use Roman techniques to build a bridge over a river that's a couple of kilometers wide that can carry heavy trucks, unless you're thinking of building a dam.

It is the same type of person that says Romans were more ecological because we have cars and they had carriages drawn by hand or by horse.

Which is to say "let's just pretend that all of those pesky details do not exist".

This is an excellent point, the tradeoffs are specific to the time, place and needs of the builders

> could you call it well-engineered?

What is well engineered depends on the goals and the limitations of the state of the art at the time. I would say that a thousand year old bridge might count as well engineered if the goal was a bridge that had a low total lifetime cost.

Why are you throwing shade at civil structural engineering?

Do all bridges we build need to be able to withstand the force of an entire shipping container bridge hitting it at high speed? What planet should an engineer think that a shipping container has managed to veer off course so badly that they hit a bridge at full speed, fully loaded? That is a sad and significant outlier event.

This is a common joke in engineering.

It’s not meant to be an insult, but a compliment noting that engineers know what the essential parts of the bridge are

I suspected it might be but I couldn't tell from the post. There is a lot of self deprecating humor amongst engineers / engineering programs.

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