The Naked Scientists

The Naked Scientists Forum

Author Topic: why are manhole covers typically round?  (Read 6640 times)

Offline erickejah

  • Sr. Member
  • ****
  • Posts: 347
  • Parking? I make my own parking spot!!
    • View Profile
why are manhole covers typically round?
« on: 25/03/2009 03:14:08 »
I was reading some possible answers for this questions in http://en.wikipedia.org/wiki/Manhole_cover do you have anymore hypothesis, use your imagination. gl ;)
« Last Edit: 25/03/2009 22:43:08 by ukmicky »


 

Offline Chemistry4me

  • Neilep Level Member
  • ******
  • Posts: 7709
    • View Profile
Re: why are manhole covers typically round?
« Reply #1 on: 25/03/2009 03:44:53 »
You can pick it up and use it as a frisbee.
 

lyner

  • Guest
Re: why are manhole covers typically round?
« Reply #2 on: 25/03/2009 09:45:43 »
because holes / shafts are stronger if they are round
« Last Edit: 25/03/2009 09:53:06 by sophiecentaur »
 

Offline Chemistry4me

  • Neilep Level Member
  • ******
  • Posts: 7709
    • View Profile
Re: why are manhole covers typically round?
« Reply #3 on: 25/03/2009 10:09:43 »
That was already mentioned in the article:

Quote
-A round manhole cover cannot fall through its circular opening, where as a square manhole cover may fall in if it were inserted diagonally in the aperture (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, and so it is natural that the cover of a round tube assume a circular shape.
-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 horizontal boring mills.
-Circular covers do not need to be rotated to align them when covering a circular manhole.
-Human beings have a roughly circular cross-section.
-A round manhole cover can be more easily moved by being rolled.
-If an automobile rolls over a dislodged manhole of another shape, the sharp corners could puncture the automobile's tire, whereas a circle doesn't have corners.
-It's easier to dig a circular hole.
-Tradition
-Aesthetics
-Supply. Most manhole covers are made by a few large companies. If you want a different shape, you will have to pay more to have them custom-made or you will have to make them yourself.

http://en.wikipedia.org/wiki/Manhole_cover
 

Offline Mazurka

  • Hero Member
  • *****
  • Posts: 510
    • View Profile
Re: why are manhole covers typically round?
« Reply #4 on: 25/03/2009 12:19:06 »
Good illustration as to why wikipedia is not the ultimate source of knowledge... ;)

-A round manhole cover cannot fall through its circular opening, where as a square manhole cover may fall in if it were inserted diagonally in the aperture (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture.)
OK, I have dropped half of a rectangular manhole cover through the frame, most frames have sufficient internal lip to make it really difficult to do so.

-Round tubes are the strongest and most material-efficient shape against the compression of the earth around them, and so it is natural that the cover of a round tube assume a circular shape.
Whilst it is physically true – that round tubes are strongest and most material efficient – these properties are seldom a factor for most manholes as they are typically an access point to a larger chamber beneath.

-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 horizontal boring mills.
Most bearing surfaces for manhole frames (in the uk at least) are cast rather than milled as it is quicker and cheaper.  Light weight manhole frames are often made from pressed steel.

-Circular covers do not need to be rotated to align them when covering a circular manhole.
True, but fitting a non circular lid is not all that difficult (as long as you don't drop it [:I]

-Human beings have a roughly circular cross-section.
  ??? [V][:I]

-A round manhole cover can be more easily moved by being rolled.
Cannot really argue with this one, although most covers have a lip to cover the manhole frame

-If an automobile rolls over a dislodged manhole of another shape, the sharp corners could puncture the automobile's tire, whereas a circle doesn't have corners.
Cannot argue but seems a little unlikely

-It's easier to dig a circular hole.
Really?  It is certainly easier to drill round holes but I have yet to see man or machine dig a perfectly round hole – particularly at manhole scale.  I have seen round precast concrete sections dropped into an excavation and the void between the concrete and excavation backfilled with earth or concrete.

-Tradition
-Aesthetics

Fair comment
-Supply. Most manhole covers are made by a few large companies. If you want a different shape, you will have to pay more to have them custom-made or you will have to make them yourself.True to an extent although it appears to be surprisingly difficult to get round manholes in the UK – most are isosceles triangles.  However whilst looking (just so I don’t make a total idiot of myself)  I stumbled across this

http://www.bbc.co.uk/dna/h2g2/A10607087
 

Offline erickejah

  • Sr. Member
  • ****
  • Posts: 347
  • Parking? I make my own parking spot!!
    • View Profile
Re: why are manhole covers typically round?
« Reply #5 on: 25/03/2009 15:32:34 »
good point of view :)
what about the symbolism of the sun Ο...
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8125
  • Thanked: 53 times
    • View Profile
Re: why are manhole covers typically round?
« Reply #6 on: 25/03/2009 16:13:48 »
Quote
-Human beings have a roughly circular cross-section.
http://en.wikipedia.org/wiki/Manhole_cover

I bet an American wrote that  :)

[Isn't the politically correct term "personhole"  :)]
 

Offline dentstudent

  • Neilep Level Member
  • ******
  • Posts: 3146
  • FOGger to the unsuspecting
    • View Profile
Re: why are manhole covers typically round?
« Reply #7 on: 25/03/2009 16:19:52 »
[Isn't the politically correct term "personhole"  :)]

Only if you live in Personchester.
 

Variola

  • Guest
Re: why are manhole covers typically round?
« Reply #8 on: 25/03/2009 18:29:19 »
Quote
Isn't the politically correct term "personhole

Sound like something anatomical to me!  [:0]
 

Offline latebind

  • Sr. Member
  • ****
  • Posts: 248
  • Hello World
    • View Profile
Re: why are manhole covers typically round?
« Reply #9 on: 25/03/2009 20:14:14 »
I would like to know why they are called 'manhole' covers?
Some better suggestions : Sewer hole cover?
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8125
  • Thanked: 53 times
    • View Profile
Re: why are manhole covers typically round?
« Reply #10 on: 25/03/2009 22:03:19 »
Some better suggestions ...

Beer money token ? ...

Quote
Thieves steal manhole covers to cash in on scrap metal
Aug 14 2008

The rocketing price of scrap metal has led to 220 manhole covers being stolen in four nights across Warwickshire.

The Local Government Association said an estimated 50,000 drain covers had been stolen this year, with thieves usually striking at night, costing councils an estimated £1.5m this year and leaving drainage systems exposed.

In the past few weeks, 20 covers were stolen on one day in Northampton and Accrington and 42 were taken in 10 days in Slough, while more than 250 covers have been stolen in Surrey since April.

Councils have to pay at least £300 to replace a drain cover.
http://www.birminghampost
« Last Edit: 25/03/2009 22:09:34 by RD »
 

lyner

  • Guest
why are manhole covers typically round?
« Reply #11 on: 25/03/2009 23:16:29 »
Having dug a round hole and needing to go to a shop for a round manhole cover I, eventually, got a round to-it.
 

The Naked Scientists Forum

why are manhole covers typically round?
« Reply #11 on: 25/03/2009 23:16:29 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length