Why manholes are round?
 

:con
plz anyone tell me k manhole k covers mostly round kyn hoty hain.
as this question is most frequently repeated in eds paper
plz btayyyyyyyyyyyyy koi.

sab say pehla tou fayeda yeh k dhakan hole k ander ne girta...
agar triangle,square ho tou woh mail hole main b gir sakta...:bow

I agree with Kashif, circular hone ka yahee faida hota hai k andar nahi girtey, kissi bhee doosri shape k andar gir sakte hain( ya phir iss cheez se bachne k lie dhakkan hole k size se ziada hee barey bnaney pren ge) round size ka thora sa bara ho hole se to no, problem.
and they say that circle is the most stable and strong shape.

Reasons for the shape include:
A round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the hole

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.

Similarly, it's easier to dig a circular hole and thus the cover is also circular.

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 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.

Tradition.

[B][I][COLOR="Olive"]In my oppinion the logic is simple that it is easier to perform cleaning operation in a round one as compared to the other shapes. The angle or penetration in round shapes is more effective in clearing away the blockages.

Waisay agar koi cover rectangular ho ya triangular to us ka base bhi us se corresponding ho ga to beech main girnay wala problem un main bhi nahin ho ga in my oppinion[/COLOR][/I][/B]

You have to be definite while writing scientific reasons. Tukkay nahin maarnay. :)

The reason for the circular construction of these covers is, quite simply, that covers of any other shape would fall through the manholes by virtue of their varying diameters. Circular manhole covers do not vary in width, or in diameter, as is the case with these other shapes, thus remaining in place despite the street traffic running roughshod over them.

Manufacturers craft the manhole covers together with the smaller sized lip, upon which they rest, at the same time to ensure a tightly sealed fit. Additionally, the manufacture of circular manhole covers is easier and more accurate than the manufacture of covers of any other shape. Lastly, round manhole covers, once removed, require less lifting and less manpower, as their shape allows them to be rolled.

[I]So Just Why *Are* Manhole Covers Round?

[/I]Well I'll tell you, but if all you want is the answer then you missed the point of the question.

"Why are manhole covers round?" is a now famous interview question considered anywhere from thought provoking to downright stupid by people on the receiving end.

Why do interviewers ask it? Well, it's so well known now that they shouldn't anymore but originally it was to see how interviewees responded. It's a way to get a sense for an interview candidate's ability to think on his or her feet outside of their area of expertise. The way the candidate approaches the problem, thinks of and presents potential solutions, defends them, or discards them are all relevant to the interviewer.

It's a simple question. There are simple answers. But the great not-so-secret about these types of questions that everyone seems to miss is that [B]it's not about the answer[/B]! The interviewer cares [I]much[/I] more about how you arrive a whatever answer you get than what that answer is. Are you thinking logically? Is there method or madness to the solutions you consider, accept, and discard? Are you even willing to entertain such an absurd question?

Oh. You still want the answer.

The most common answer is simply that a round manhole cover can't fall into the hole it covers. But I did tell you that there's more than one answer. Heavy, round manhole covers are easier for one person to move by standing it on end and rolling. Also, you don't have to "align" a manhole cover to it's hole. Any orientation will do.

My father, a mechanical engineer, claimed an answer I hadn't heard before: that round manhole covers are easier to manufacture. That's a nifty answer and it would have done great in the interview except he also claimed that was the [I]only[/I] reason and all the others were wrong. Whoops.
And for the record, round is not the ONLY shape that can't fall into its hole. There's a class of such shapes referred to as "[URL="http://ask-leo.com/r-30917a"]Reuleaux polygons[/URL]". The common characteristic is that they share a constant width or diameter.

Source : [URL]http://ask-leo.com/so_just_why_are_manhole_covers_round.html[/URL]

@fawadkhan

That was my point if any other shape can fall in he hole then why can't the round ones and if round ones cannot fall them how come others will fall in the hole coz the frame for the cover to rest upon is made according to it's shape

I have three main holes though smaller in size in my own house for drainage purpose and they are rectangular in shape and they have never fallen in side.

May be you all answers are true to some extent that, round shape easy to manufacture, easy to roll, low probability of falling inside etc etc...
But i think it is historically evidence fact that its shape was round till The Great Mughalian period, so simply no body try to change it:clap

The question of why manhole covers are typically round, at least in the U.S., was made famous by Microsoft when they began asking it as a job-interview question.Originally meant as a psychological assessment of how one approaches a question with more than one correct answer, the problem has produced a number of alternate explanations, from the pragmatic ("Manhole covers are round because manholes are round.") to the philosophical.

Reasons for the shape include:
[LIST][/LIST]A round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the hole. (A Reuleaux triangle or other curve of constant width would also serve this purpose, but round covers are much easier to manufacture. 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.)
[LIST][/LIST]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.
Similarly, it's easier to dig a circular hole and thus the cover is also circular. [LIST][/LIST]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 them when covering a circular manhole. [LIST][/LIST]Human beings have a roughly circular cross-section.
A round manhole cover can be more easily moved by being rolled.
Tradition. [LIST][/LIST]Supply. Most manhole covers are made by a few large companies. A different shape would have to be custom made.
Other manhole shapes can be found, usually squares or rectangles. Nashua, New Hampshire may be unique in the U.S. for having triangular manhole covers that point in the direction of the underlying flow. The city is phasing out the triangles, which were made by a local foundry, because they are not large enough to meet modern safety standards, and larger triangles cannot be found.[

Well I personally think its something relating to the weight which is put over it.

If we step over a round manhole our weight would eventually apply equally on all sides of the manhole thus making a very strong hold. While, I think, it is not the case in the square or round cornered manholes.

Round Or Circular Mainholes lid...
 

dear frnds all of ur explinatins are praise worthy bt the main reason fr a circular cover of mainholes is that every where the drainage system or the passage ways fr certain purposes are made in round shapes and to cover their surfaces one have to provide such protection which should be durable and convenient,
Thats why circular shapes fit it more feasibly coz circular shapes lids or covers never fall into the circular holes because of its geomatery.

So simple and logical.

[QUOTE=zeeshan1001;185991]Well I personally think its something relating to the weight which is put over it.

If we step over a round manhole our weight would eventually apply equally on all sides of the manhole thus making a very strong hold. While, I think, it is not the case in the square or round cornered manholes.[/QUOTE]

Weight ACTS VERTICALLY DOWNWARDS.It is the force exerted on an object by the earth(the product of an object's mass and acceleration due to gravity).It always acts vertically downwards regardless of the shape of the underlying surface.

I know it sounds like fifth grade stuff but I had to put the record straight.

stresses produced by the surface load (vehicles etc) can be uniformly distributed along the circular bodies which causes the minimum strain(deformations in bodies) in overall body against the higher values of stresses..moreover, the value of radius of gyration of circular bodies causes the higher strength of circular shaped bodies.. that is why circular shaped columns are preferred in multistory buildings or even in house construction and also circular shaped manholes covers are preferred.

I think this discription will be helpfull. It is a simple case of three dimensional arch-truss. :thinking Go through this explanation.
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[SIZE="4"][SIZE="3"]@ faseeh
[SIZE="2"]Bro if it acts like an [B]"arch"[/B] then it shud be v weak in tension and strong in compression..then how does the manhole absorb the tensile forces???? [/SIZE] [/SIZE][/SIZE]

[QUOTE=Ayaz9;199711][SIZE="4"][SIZE="3"]@ faseeh
[SIZE="2"]Bro if it acts like an [B]"arch"[/B] then it shud be v weak in tension and strong in compression..then how does the manhole absorb the tensile forces???? [/SIZE] [/SIZE][/SIZE][/QUOTE]

It is not actually tensile but Compressive forces that main holes suffers, another type of stresses that it may suffer is hoop stress that is specific to curved surfaces and is present is the outlined curve of the body. (Details of hoop stress is beyond the scope of this thread, any one interested may google the topic or consult Text Book of Machine Design by Khurmi & Guptta or Elements of Machine Design by Shiglay. ;))

The logic behind this, is easy to understand if we keep ourselves in place of a sanitary worker.
1. Think, if there would be a shape of manhole, having corners then would it be an easy task to go inside it for cleaning? Circle is a shape which is uniform as it has the same distance from its centre to every point on it. So, it is easy to get inside it or to do any task.
2. Now be a civil engineer. The severiage lines are, usually, circular and manholes are cross sections on them. So, every cross section should be round even the line is not circular.

[QUOTE]The logic behind this, is easy to understand if we keep ourselves in place of a sanitary worker.
1. Think, if there would be a shape of manhole, having corners then would it be an easy task to go inside it for cleaning? Circle is a shape which is uniform as it has the same distance from its centre to every point on it. So, it is easy to get inside it or to do any task.[/QUOTE]

It will be worth mentioning that a circular disc with a certain dia will have [B]less area[/B] then a square of the sides equal to that dia. So which is easier for a sanitery worker to use???

[ATTACH]3345[/ATTACH]
[QUOTE]2. Now be a civil engineer. The severiage lines are, usually, circular and manholes are cross sections on them. So, every cross section should be round even the line is not circular. [/QUOTE]

Practically the cross section of underground lines are circular but the section that reaches ground is square or rectangular in section, with provision made for mainhole cover by placing a mainhole seat with mainhole cover. see this pic...
[ATTACH]3346[/ATTACH]

In my opinion it is only the unique ability of circular disc to bear extra ordinary stresses that mailhole are made in this fasion. Another example is that of Pyramids in Egypt. If you over lap the structre of a tetrahedron on a circular disc you will get the same figure that i post in my last post & since the stability of Pyramids is well known you will get the required answer for mainholes.

The question's answer is simple and involves only a basic knowledge of 'Distribution of Stress (Force) among various materials' and is as follows alongwith the necessary scientific explanation at first,

[B]Scientific Explanation:[/B]
If we apply a force or exert stress on an object then its distribution is most uniform if the object is circular in shape.

[B]What does this mean?[/B]
It means if a car, say of 1000kg, has to pass over a manhole then the required strength of manhole will be achieved with less thinkness (and utilization of raw-material) if the every small part of manhole bears this weight equally. Since 'Circular Shape' is the one which has maximum uniform distribution of forces so we can produce the required manhole with less consumption of raw-material in a minimum cost.

[B]Answer:[/B]
"A manhole is manufactured in a round shape because this shape offers best endurance because of even distribution of stress"

[B]Other Illustrations:[/B]
You will definitely have seen big structures having pillars to support their roofs. Have you ever noticed that their pillars are always circular in shape? If not, then see those. May be you have a one at your own home!

From answers stated in the earlier posts, i only agree with the one that supplements the above anser is that 'Circular Shape has an added advantage of being easy in transportation' but this is not the main reason because if Square or Rectangular Shape had more proper distribution of forces then convenience of transportation would surely have been forgotten.

I have been trying to state same in last two posts. In no other shape the stress can be so uniformaly distributed as it can be in case of a circular disk. In case of any figure with corners, [B]The stress will concentrate on the coners that will soon be razed to particles and there will be a defect in the main hole.[/B] :D

@ faseeh

[SIZE="3"]will u agree with me the effect of constant radius of gyration of circular bodies ,which helps to distribute the stresses uniformly????? hope stress is different concept, usually can be observe in doom structures and manhole does not act like a doom .....[/SIZE]

Firstly Circle have equal diameter on all side so any pressure falling on it is equally balanced by all side.
Secondly,Any object in circular shape is easy to move
Thirdly,Mainhole have been manufacture in circular shape from inception.These have been taken as best and no body tried to change.

Stress Explained...
 

[QUOTE]@faseeh
will u agree with me the effect of constant radius of gyration of circular bodies ,which helps to distribute the stresses uniformly????? hope stress is different concept, usually can be observe in doom structures and manhole does not act like a doom .....[/QUOTE]

Stress can be observed any where. The radius of gyration (r) describes the way in which the area of a cross-section is distributed around an objects centroidal axis (Centriod means mass-center). Fory symmetrical objects, like this ciruclar disc, the radius of gyration, gemetric-center & mass-center(centriod) will be the same & thus the stress will be distributed Uniformlly.

In lines bellow I will explain types of stress and then will conduct a subjective analysis of types of stresses that are found in main holes which will show how stress is the main factor in its design.

[U][B]Stress:[/B][/U]
Stress in produced by application of force. So we can safely classify stress on the basis of force causes Stress & resulting in Strain.

[B]Tensile Stress: [Figure#1][/B]
When a force acts on an object perpendicular to its surface & opposite in direction, the stress produced is called Tensile Stress.

[B]Examples:[/B]
1. When children try to pull rope in opposite direction this type of stress is found in Rope.
2. When we tear paper in to two peaces we apply tensile stress.
3. When we try to expand a rubber band we are applying tensile stress.

[B]Compressive Stress: [Figure#2][/B]

When a force acts on an object in same direction and perpendicular to the surface, the stress produced is called Compressive Stress.

[B]Example:[/B]

1. When we push the door the stress produced in the door is compressive stress. (Although it is not visible).
2. When we sit on our bed, the stress produced in mattress is compressive stress.

[B]Dynamic Stress [Figure#3] [/B]

Dynamic stress is created by intermittent application of load. As the name depicts, dynamic means it varies between a minimum and a maximum value, it is often called Cyclic Stress (especially when we study “Mechanical Vibrations”, in that case.)

[B]Examples:[/B]
1. When we press the door bell, the stress produced in the spring is dynamic stress.
2. The jumpers of Motorcycles & Cars experiences regularly Dynamic Stress.
3. Even when we use stairs, muscles in our leg experience dynamic stress when we try to step-up. (Max load when we try to step-up, when we complete the step, it is the min load of cycle).

[B]Dead Stress: [Figure#4][/B]
Dead stress is caused by dead-loads, the one which is still and does not move for long time.

[B]Example:[/B]

1. To me the classic example is sagging in the power cable. Do you know why they turn into an arc? (In urdu Sag means “Latak Jana” or “Jhool A Jana”), it is because due to dead weight of cable that is starts sagging.

[B]Shear Stress: [Figure#5] [/B]

It is a stress produced by application of force parallel to the plain. (Normal stress is applied perpendicular to the plane)

1. Stress produced by scissors blade is shear stress.
2. When we try to take butter from butter tablet the stress applied is shear stress.


[B]Thermal Stress [Figure#6] [/B]

It is produced by the temperature difference. Thermal stress is produced in bodies that are experiences temperature gradients over their surface.

1. Glass fitted in a window and exposed to sun light.
2. Stove when fired.
3. Utensils when used in kitchens.

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[U][B]Which stresses are applied on Main-Holes.[/B][/U]

[B]Tensile Stress: [/B]
No. This type of stress certainly does not apply here.

[B]Compressive Stress: [/B]
Yes. When a vehicle is parked over a main hole or due to red light the tyre of car rests on the main hole, the stress applied is compressive stress.

[B]Dynamic Stress:[/B]
Yes, when a vehicle is passed over the main hole it experiences dynamic stress.

[B]Dead Stress:[/B]
Yes, when a vehicle is parked over it. Same as in compressive stress.

[B]Shear Stress:[/B]
No. No force is applied parallel the surface. All forces act perpendicular to the surface for main hole.

[B]Thermal Stress:[/B]
Applicable but to negligible level.

[B]Conclusion:[/B]
Thus by study of definations and examples above mentioned, the only reason that appears most convinceing is its unique ability to bear load (Stress). The only reason else to it that is technical is the point that it will not fall into it, while rest of the shapes can pass through it.

Thus if designed uncorrectly, it can easily be razed to particles, due to the immense load it bears on regular basis when vehicals moves, rests and bumps over it.

Your question & criticism are welcomed, but be innovative and donot repeat questions. :D