4 ms·

Isn't the round manhole covers just to make sure they can't fall in?

Retric 8y ago
It’s actually several things. It’s stronger, cheaper, rolls, lighter, no need for alignment etc. You can make sure any shape does not fall in, but strength to weight ratio is important as you want people to open them with hand tools while supporting dump trucks. PS: At ~250 lb you can see why a less optimal shape might be a problem.
- m0zg 8y ago
  It's also utterly irrelevant to the software engineering profession.
deleted 8y ago
[deleted]
twodave 8y ago
Less raw materials to produce, easier to transport by rolling, easier to place onto the manhole, easier to stack when transporting/storing in bulk, etc
- JustSomeNobody 8y ago
  Flies like a frisbee when Superman throws it...
  - werkjohann 8y ago
    Or better - Elastigirl! https://twitter.com/SamuelGavin/status/1008636415524171776 https://twitter.com/SamuelGavin/status/1008636415524171776
antaviana 8y ago
According to the Wikipedia [1] Reasons for the shape might include: * A round manhole cover cannot fall through its circular opening, whereas a square manhole cover might fall in if it were inserted diagonally in the hole. The existence of a "lip" holding up the lid means that the underlying hole is smaller than the cover, so that other shapes might suffice. (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.) * Round tubes are the strongest and most material-efficient shape against the compression of the earth around them. * A round manhole cover of a given diameter has a smaller surface area than a square cover of the same width, thus less material is needed to cast the manhole cover, meaning lower cost. * The bearing surfaces of manhole frames and covers are machined to assure flatness and prevent them from becoming dislodged by traffic. Round castings are much easier to machine using a lathe. * Circular covers do not need to be rotated to align with the manhole. * A round manhole cover can be more easily moved by being rolled. * A round manhole cover can be easily locked in place with a quarter turn (as is done in countries like France), which makes them hard to open without a special tool. Lockable covers do not have to be made as heavy, because traffic passing over them cannot lift them up by suction. [1] https://en.wikipedia.org/wiki/Manhole_cover https://en.wikipedia.org/wiki/Manhole_cover
- walshemj 8y ago
  Ironically all the utility covers I see in the UK are square. I also think the casting argument is a good one and its a lot easier to cast a round object than a square one (its to do with how molten metal flows)
- derefr 8y ago
  Don't forget also: round manhole covers are a Schelling point. Making a manhole cover round is one of the first intuitive shapes you'd think to make them (along with squares and rectangles); and so you'd guess, as a construction company gearing up to sell the concept of concrete manholes with removable iron-plate covers to a municipality (back in the 1800s or whenever we first got them) that what the municipality will ask you to make is round manhole covers. So you provisionally set up your tooling for round manhole covers, and build a few for the demo. And the municipality assumes you're the expert about good manhole-cover shapes, and so just goes with the flow, rather than trying to figure out the best shape themselves. So you end up with "the first intuitive thing that worked" spreading via network/"system compatibility" effects. Same with road widths; same with screw drives.
FigBug 8y ago
The covers are round because the holes are round. :P
- commandlinefan 8y ago
  You’re hired!
commandlinefan 8y ago
That’s exactly why they’ve given up the brain teaser questions - all it checks is whether somebody’s told you the answer before.

It’s actually several things. It’s stronger, cheaper, rolls, lighter, no need for alignment etc. You can make sure any shape does not fall in, but strength to weight ratio is important as you want people to open them with hand tools while supporting dump trucks. PS: At ~250 lb you can see why a less optimal shape might be a problem.

m0zg 8y ago
It's also utterly irrelevant to the software engineering profession.

deleted 8y ago

[deleted]

twodave 8y ago

Less raw materials to produce, easier to transport by rolling, easier to place onto the manhole, easier to stack when transporting/storing in bulk, etc

JustSomeNobody 8y ago
Flies like a frisbee when Superman throws it...
- werkjohann 8y ago
  Or better - Elastigirl! https://twitter.com/SamuelGavin/status/1008636415524171776 https://twitter.com/SamuelGavin/status/1008636415524171776

antaviana 8y ago

According to the Wikipedia [1] Reasons for the shape might include: * A round manhole cover cannot fall through its circular opening, whereas a square manhole cover might fall in if it were inserted diagonally in the hole. The existence of a "lip" holding up the lid means that the underlying hole is smaller than the cover, so that other shapes might suffice. (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.) * Round tubes are the strongest and most material-efficient shape against the compression of the earth around them. * A round manhole cover of a given diameter has a smaller surface area than a square cover of the same width, thus less material is needed to cast the manhole cover, meaning lower cost. * The bearing surfaces of manhole frames and covers are machined to assure flatness and prevent them from becoming dislodged by traffic. Round castings are much easier to machine using a lathe. * Circular covers do not need to be rotated to align with the manhole. * A round manhole cover can be more easily moved by being rolled. * A round manhole cover can be easily locked in place with a quarter turn (as is done in countries like France), which makes them hard to open without a special tool. Lockable covers do not have to be made as heavy, because traffic passing over them cannot lift them up by suction. [1] https://en.wikipedia.org/wiki/Manhole_cover https://en.wikipedia.org/wiki/Manhole_cover

walshemj 8y ago
Ironically all the utility covers I see in the UK are square. I also think the casting argument is a good one and its a lot easier to cast a round object than a square one (its to do with how molten metal flows)
derefr 8y ago
Don't forget also: round manhole covers are a Schelling point. Making a manhole cover round is one of the first intuitive shapes you'd think to make them (along with squares and rectangles); and so you'd guess, as a construction company gearing up to sell the concept of concrete manholes with removable iron-plate covers to a municipality (back in the 1800s or whenever we first got them) that what the municipality will ask you to make is round manhole covers. So you provisionally set up your tooling for round manhole covers, and build a few for the demo. And the municipality assumes you're the expert about good manhole-cover shapes, and so just goes with the flow, rather than trying to figure out the best shape themselves. So you end up with "the first intuitive thing that worked" spreading via network/"system compatibility" effects. Same with road widths; same with screw drives.

FigBug 8y ago

The covers are round because the holes are round. :P

commandlinefan 8y ago
You’re hired!

commandlinefan 8y ago

That’s exactly why they’ve given up the brain teaser questions - all it checks is whether somebody’s told you the answer before.