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Looking around it appears that bricks, through history, have been constructed in cuboid form i.e. with six faces at right-angles to each other. This is also apparently the case with stone construction too - six-sided volumes.

Is the cuboid form the most efficient form to bear load?

How do other form stack up?

EDIT: I would argue in favour of a shape such as a pyramid. It would take more effort to fabricate & work. But it may also be better able to bear load - perhaps because of the way the edges dovetail.

Does the cuboid form continue merely because of the psychological inertia that the term 'brick' induces the impression of a cuboid or near cuboid (as in ingots) form, and because the cuboid form is the easiest to grip/position by the mason/robot?

Why are bricks typically constructed to have six faces at, or near right-angles to each the other?

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I don't actually see any physics in this. Compare to physics.stackexchange.com/questions/9045/… . The mathematics of packing come into play and the ease of manufacture, but neither of these things is physics. Likewise aesthetics. –  dmckee Jul 26 '12 at 14:30
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@dmckee the question asks "is the cuboid form the most efficient form to bear load". That's a physics question, and physics very much does come into play in answering it. (If the top and bottom surfaces are not parallel then the next brick is on an inclined plane, hence less gravitationally stable, all other things being equal.) –  Nathaniel Jul 26 '12 at 15:45
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@Nathaniel OK. I'll buy that. –  dmckee Jul 26 '12 at 15:53
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3 Answers 3

up vote 2 down vote accepted

Since I argued to re-open this question I should put the effort in to answer it :)

As other answers have pointed out, there are important cultural reasons why we use cubical bricks, and different architectural traditions may predominantly use bricks of different shapes. Not all bricks are cuboid - if you look at a brick building that contains arches (such as an old bridge or railway station) you will find that it contains bricks that are not quite cuboid in shape. However, I would say that cuboid bricks are the optimal shape for the purpose they're designed for, which is to build relatively thin straight-sided vertical walls that are usually at right-angles to one another.

The first consideration is that the wall needs to be straight. Having the top and bottom surfaces of the brick parallel to one another is a good way to do this. You could do it in other ways. For example, by using bricks that are trapezoidal in cross-section. The picture below illustrates this, along with the problem it would bring:

trapezoidal bricks

Although the wall would be straight-sided, each brick is sitting on an inclined plane, and thus wants to slide out sideways. Although the mortar would prevent this, such a wall would be less stable, and also less practical to build.

Of course, if you want to build an arch or an igloo then this is exactly the sort of brick you need, and if you look at an arch you will see this type of brick:

enter image description here

but this takes us away from our design goal of a vertical wall.

So if you want to build a straight-sided vertical wall then the bricks need to be rectangular in cross-section. This only leaves the "end" surfaces, which in theory could be at any angle as long as they tesselate. However, making them be at right-angles to the other two sides makes it easy to build two walls that join at right-angles without needing to break any bricks, like this:

enter image description here

This also contrains the length of the sides a bit - the bricks must be twice as wide as they are deep in order for that to work. The only free parameter is the height of the brick, which can vary depending on the type of brick. (Think of the shape of a breeze block compared to a red brick.)

So although there are other types of brick suitable for other purposes, the cuboid form is very good for building rectangular-sided buildings with straight walls, and I would say that the design has survived throughout history because of this.

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Erm. I may be prejudiced in favour of the pyramid form, but wouldn't six pyramids edge-to-edge inwards form a cube which could not slip? –  Everyone Jul 29 '12 at 11:39
    
Never mind (+: Just realized I was back on the cube-form by coalescing the pyramids edge-to-edge –  Everyone Jul 29 '12 at 11:46
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@Everyone if you build a cube out of six pyramids then the top one is effectively balancing on top of the bottom one, tip to tip. If it moves even just a little bit then it will start to slide down one of the sides of the bottom pyramid, pushing one of the side pyramids out of the way as it does so. Try making some papercraft pyramids and stacking them into a cube this way - I think you will find it falls apart very easily unless you glue them together. –  Nathaniel Jul 29 '12 at 14:03
    
I would argue that structure in fig 1, although susceptible to shear is more resistant to earthquakes -- small yields are better than total collapse. Some soft buffer material, e.g. sand or hay or wool is probably required though. –  qarma Apr 4 at 9:09
    
@qarma there may be some truth in that. The bases of traditional Japanese castles are built from irregularly shaped stones and are remarkably earthquake-resistant; conversely, living in Japan, I rarely if ever see a wall built of rectangular bricks (though they are sometimes used as cladding over concrete structures), and I think earthquakes are part of the reason. (But I think the design I drew above would not be particularly good, as it would collapse just as easily as a brick wall. The irregular blocks need to lean against one another for it to work as an earthquake resistant structure.) –  Nathaniel Apr 4 at 9:29
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It is a cultural remark, in Japan, the stone bricks are not cubical. They are shaped in a way the wall falls on itself. It is much more efficient against earthquakes.

http://www.japanese-castle-explorer.com/castle_profile.html?name=Funai

Cubical form started in mesopotamia 5000 years ago when they were moulding the bricks.

http://janestreetclayworks.com/2011/02/16/the-history-of-bricks-mesopotamia/

The problem of finding a shape succeptible to tile the space is not an easy one, even in a plane. So from a practical point of view it makes sense to simply use cubical bricks.

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Could you add a short description on what to find on the first link? The link is not broken, but it looks like the target has changed. –  Volker Siegel Apr 3 at 23:28
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Well of course it's far more practical to make rectangular bricks where their sides ensure the floors and walls are horizontal and vertical, while at the same time creating two walls and a floor/ceiling at the same time. They're also rectangular rather than cubical so that the bricks over lap one another vertically for greater strength.

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