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Why are manhole covers round and not square?
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Why are manhole covers round and not square?
18,810 Views | (34 votes, avg: 3.85)
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3 reasons:–
1. The “No Corner” theory : That it can be easily pushed up, after fitting once, from any side.
2. The “Easy Moving” theory : That it can be rotated to the desired hole easily
3. The “Big Bang” theory, I like it most, is that the first one who designed manhole, made it round, for round is the shape of any unstructured hole so, the cover is also round.
Reduction of the area without sacrificing of its diameter/accessibility results in using less weight and therefore chipper and easier to handle manhole cover.
The way I see it the answer has to do with basic geometry. Any shape other than round (square, rectangle, etc) opens the possiblility of the manhole to turn over along an axis (could be any axis) and cause injuries to people. Simplest example would be that of a square in which the diagonal is longer than any of the sides. So a square cover has the possiblility of turning over and falling vertically in along the diagonal of the hole.
One answer can be this:
Let two parallel lines touch a given circle. The distance between the two of them, irrespective of how they are placed, is always the same. Hence, one can never drop a circular lid into the manhole it covers. This is not the case with squares,of course, and hence they can’t be used as manhole lids. However, from this point of view, the Rouleux triangle, which shares the abovesaid property with circles, can be considered as an alternative.
3 reasons:–
1. The “No Corner” theory : That it can be easily pushed up, after fitting once, from any side.
2. The “Easy Moving” theory : That it can be rotated to the desired hole easily
3. Most Important: Let two parallel lines touch a given circle. The distance between the two of them, irrespective of how they are placed, is always the same. Hence, one can never drop a circular lid into the manhole it covers. This is not the case with squares,of course, and hence they can’t be used as manhole lids. However, from this point of view, the Rouleux triangle, which shares the abovesaid property with circles, can be considered as an alternative.
A round manhole cover can never fall into the manhole!
Any other shape can fall into the manhole, except an equilateral triangle. But triangular cast-iron manhole is weaker compared to a round one.
Obviously, anyone can throw a square manhole cover inside the manhole.
In addition to the answres above, don’t forget about these two:
4. Cost savings. Round manhole covers require less material than any other man sized shape.
5. Manhole covers are round because manholes are round.
1. Falling - A round cover cannot fall into a round hole. A square cover can fall along any angle between its side and diagonal (i.e at any angle between 0 and 45 degrees).
2. Edges - Any shape other than circle will have at least one sharp edge which means they are more prone to causing injuries to repair-men.
3. Mech engg - A circular shape is the most easy in the world to forge or cast.
4. Transportation - A circle has the property that for a given circumference, it takes the least area. In other words, for a given volume of metal a circle shape will occupy least area on the shop floor or on the transporting vehicle!
5. Transportation - A circular cover can be rolled over on its side during repairs.
6. Distribution - Any force applied on a circle is equally perceived at every point on its edge. When you design a circular manhole, you make sure the wear and tear on the supporting concrete is uniform. Not so for other shapes, where the forces will be concentrated on the corners and they wear more.
First, manhole covers aren’t always round, they are sometimes rectangular and perhaps other shapes.
Most of them are probably round, so maybe the better question is “Why are most manholes round?”
Answer: Because manholes are usually built to access sewer systems which are generally constructed using cylindrical pipes. There are many reasons for this including economy of materials, strength, and flow of materials through the conduits.
If you ask a construction engineer to build an access to a system mostly constructed from pipes, he will most likely stick a pipe on its end - which is round.
1 - cost - it’s easier and cheaper to manufacture round than other shapes, the almighty dollar takes preference over all.
2- mobility - you can roll the heavy object as not all would be able to lift, and most workers are lazy
3- safety - so they don’t fall through the hole (notice this is last)
A round manhole doesnot create any gap when you rotate it in a clockwise or anti-clockwise direction, whereas a Square manhole creates triangular gap on all the 4 sides when it is rotated from 0 to 45 to 90 degrees.
Manholes are used mostly in the sewage, and gaps allow the foul smell to enter the atmosphere.
Round manholes are safer, it serves the purpose to the fullest.
Assume length of oneside of square manhole lid as ‘x’. Then diagonal length of man hole=1.414x.
So u can put the lid along the diagonal. it will get into the hole easily. But circular lid matched with circular hole never fails to cover by falling inside the hole.
This was explanied by someone else above but i think not by mathamatical way
if the manhole cover is round it won’t go inside the hole(how ever you try)…all other shapes square,rectangle etc will go inside the hole through some or the other positions(tilting ,rotating etc).
The one and only main aspect of the round shape of the manhole to be round is it’s perfect symmetry. We can keep it oval, but when the lid gets tilt in the way so that the smaller diameter of the lid comes on the bigger diameter of the manhole it will drop inside the manhole. In the same way, if the manhole is square, rectangular or any other shape, any edge of it has the probability to get the sorter edge of he lid.
In this way it is not safe. But the round shaped lid won’t get this problem, and never fall inside the manhole.
manholes are shaped round because the circular shape will use the least area and hence the least amount of material (in this metal). the circular shape minimizes the area required - hence the material required for manufacturing.
How do we know they’re all round?
the title for this would be: MINIMAL REQUIREMENTS
manholes are round because the humans are used to digging round holes(less effort), and because natural holes in the environment also take this shape.
thus
- men associated the round shape with the holes, so they stick to their presumption that holes and hole covers should be round
- corners are unnecessary. we’re simply lazy, as humans, and we would do squared holes and covers only for aesthetic purposes - see burrial places where the family wants a honorable thingie - squared hole. but in the wild, wild west, i bet they sticked to rounded holes… making no effort
i agree to Anand views on the technical aspect, and i wish to add another point.
acesses to these covers are mostly ENCLOSED SPACES, this means spaces with oxygen less than 21%, entering this space need an breathing apparatus, which is to be worn at the time of entry. since this apparatus is worn on the backof men( looks like a diving gear), this requires more space. normally the ladder to these spaces are located on one edge of the manhole, hence giving an unobstructed space while entering.
Manhole covers are round because a round metal plate will support weight better than a square one.
Because if any object comes over circular manhole then the pressure is more equally distributed at all the supporting points of the manhole as compared to other shapes of manholes.
why so much discussion old question ??
because round things fit in round boxes
Not all are:
http://www.drainspotting.com/mirror/nhtelegraph-2003-11-26/
The reason is because a circle is the only object where no matter which way you turn it, or what axis you turn it on, it will never be able to fall in. Take a square for example, if you turn it vertically, it can fall into the diagonal frame.
Becuase holes are round and not square. We are talking about the cover and not the hole itself right?
Agree with most of the above posts.
But we need to see that the round manhole covers are used to cover pipes (round). If there weren’t round pipes, there wouldn’t be round manholes! Would you have a round door to your house if the shape of the door built into the house is rectangular? So the question should now be why are there round pipes? And of course, you all know the answer!
i agree with john may be circular shape will take more load on the cover and the ircular wall under ground will take more load from the soil.Hence the low level inspection chambers will always square or rectangle in shape while manhole which will more in depths comapre other inspection chambers are circular or round in shape.
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