Technical Journal — Think Round

Disaster averted!

Everyone in the house was oblivious to the large, heavy dump-truck rolling towards them. Nobody knew the driver parked it on the hill. Nobody knew the parking brake wasn’t set. And nobody knew it was coming. The massive tons of steel slammed into the house, threatening to destroy it and everyone inside. There was a loud crash, then nothing. The house stopped the truck. The only damage was a small six-inch hole in the bedroom wall.

“How could this be?” someone asked. “This truck should have destroyed the entire home.”

A normal home perhaps. A home built of wood and plaster would have collapsed like a cardboard box. But this was a Monolithic Dome.

Actually, it was my grandmother’s house and I don’t think anyone said anything. However, the story is true. Her dome home stopped the dump truck when any other home would have been demolished. It was a dramatic demonstration of the physical strength of a Monolithic Dome.

Other advantages

But there are other advantages of a Monolithic Dome over conventionally built structures. Monolithic Domes use materials more efficiently. They require half as much energy to heat or cool. Monolithic Domes will last for centuries. And they are aesthetically pleasing.

How does a dome use materials more efficiently?

Imagine you are building three small fences. You have 32 feet of material for each fence, and you want each fence to surround as much land as possible.

What shape should you use? You experiment by building the first fence as a rectangle 12 feet long by 4 feet wide. The area bounded by the fence is 48 square feet. Next you try a square fence 8 feet by 8 feet. It’s area is 64 square feet, or a little better.

What if your last fence is circular? A circle with a radius of 5 feet 1 inch would use all 32 feet of material and its area would be 81.5 square feet. That is 33.5 square feet more than the rectangular fence! Each fence used the same amount of material, but the circular one used the material best.

This principle applies to spheres and cubes too.

Imagine you are building a water tank: 8 feet high, 8 feet wide, and 8 feet deep. You would need exactly 384 square feet of material to build it. It would hold exactly 512 cubic feet of water.

A spherical tank measuring 5 feet 6 inches in radius will use all 384 square feet of material too. But it will hold 707.6 cubic feet of water – 195.6 cubic feet more than the cubic tank. Again, both tanks used the same amount of material, but the spherical tank used it more efficiently.

Round savings!

A dome, therefore, will always use less material to cover the same space utilized by a square conventional building. Less material means less cost, or higher quality materials for the same cost, or both.

Domes are energy efficient.

To illustrate one aspect of the energy efficiency, think about the tanks we have just built. How much volume is in the cubical tank? How much in the spherical tank? If you put 200 degree water in both tanks, which tank will cool to room temperature quicker?

Think about it this way: If you cut a one-inch hole into both tanks, which would empty first? Obviously, the square tank would, because it contains less water.

Energy works in a similar way. The heat in the tanks must radiate through the material. More surface area of material dissipates energy faster than less surface area. Since both tanks used the same amount of material, the spherical tank must radiate longer to remove the heat from its greater volume of water.

The tank’s energy efficiency is measured by how well it maintains a constant level of energy. Let’s imagine that the spherical tank shrunk to the volume of the cubical tank. If volumes are identical, then the sphere would have less surface area of material. Less material dissipates heat slower, and the sphere would maintain its temperature longer. The cubical tank would require about 15% more energy than the spherical tank to maintain the same temperature.

In a house, the volume of air inside acts in the same way. A dome home would dissipate the heat slower per volume of air inside.

In Monolithic Domes, the walls are a composite of a roofing membrane, foam insulation, and steel-reinforced concrete. With the concrete inside and the insulation outside, the concrete is protected from the outside elements. Concrete, which conducts and holds heat easily, absorbs the differences in the interior temperature over the day. During the night, the concrete radiates energy back into the interior. This ‘flywheel’ action dramatically reduces the temperature variations between the day and night.

So my grandmother’s house used less material and is more energy efficient. We have also established its extreme strength.

How strong and what makes it that way?

Why would a Monolithic Dome last for centuries instead of decades? To illustrate these advantages, we need to examine the nature of gravity and its effect on a structure.

A man, for example, may support a fifteen-foot wooden pole “in a vertical position with the palm of his hand outstretched from his downwardly oriented arm. Small and continuous motions of the hand will keep the pole in vertical balance” (Fuller 153).

Anyone who has balanced a broom stick knows this is easy. The entire weight of the pole is focused down into the man’s hand. Yet, if the same man tries to hold the pole horizontally, he will fail.

Gravity is operating on the whole length of the pole. The pole would form a lever against the man with a “forty-eight to one advantage, resulting in a twelve-hundred-pound loading of the muscle tissue” (Fuller 153). No one can hold that much weight with even two hands, let alone one.

Gravity is the worst enemy of a building. Just as the man could hold the pole vertically and not horizontally, a vertical wall or column stands against gravity better than a horizontal roof or raised floor. “Columns are easy; beams are difficult” (Fuller 154). History’s ruins have proved that walls and columns stand the longest.

“Rarely are the horizontal beams, elevated floorings or roofs found to be intact, if at all, with the exception of domes which combine both horizontal and vertical behaviors … synergistically. Domes of Istanbul, the Near East and India … have been standing for centuries – the Pantheon of Rome for two millenniums, and the tomb domes of Greece for three and one half millenniums – in better condition than their contemporary and much later column-and-wall neighbors of antiquity. Not so antique, but of sad significance, the Japanese have made an historical monument of the dimensionally unaltered dome framing of the only structure that remained at target zero of the first atomic bomb dropped upon Hiroshima in 1945” (Fuller 154).

The double curve

This double curve, the combination of vertical and horizontal components, makes a dome strong.

A Monolithic Dome is a thin shell structure similar to ordinary chicken eggs. For its diminutive size and “fragile” reputation, an egg is remarkably strong.

Try this experiment: Clasp your hands in front of you – be sure to interlock your fingers. Pull your palms apart so your hands form a cup. Place an egg lengthwise in this cup. In other words, the egg should be longest from one palm to the other. Now push your palms together as hard as you can – trying to break the egg. You will not be able to do it.

The first time I tried that experiment I couldn’t believe it. I have only seen one person break the egg, but only after an extreme effort that left an impression in his palms for nearly a day.

It is the double curve of the egg that distributes pressure evenly throughout the shell (Figure 4). Most of the pressure is transferred to the other side of the egg and into the person’s other palm. Stress does not concentrate on one spot, therefore, the shell does not break.

A dome works in the same manner.

When the dump-truck hit my grandmother’s house, the force of the impact was spread throughout the dome’s shell. The mass, weight, size and strength of the entire Monolithic Dome opposed the truck and prevented all but a little damage. The truck had been rolling backward and it struck the dome with the corner of the truck’s back. All the truck’s force was concentrated, overcoming the local strength of the concrete at that point, thus creating a hole. If the truck had hit more squarely, the force would have been spread over a greater area and the dome would not have a hole in it.

Dr. Arnold Wilson, engineer and former professor at Brigham Young University, extensively studies and engineers Monolithic Domes. He said, “A Monolithic Dome is probably the most disaster resistant building that can be built without going underground or into a mountain”. (Dr. Wilson retired as Senior Consulting Engineer for Monolithic in 2007.)

Furthermore, these domes will survive direct hits from tornadoes and hurricanes, they will withstand strong earthquakes, and even make good fallout shelters. A Monolithic Dome at Port Arthur, Texas has been hit by three hurricanes, but a “hurricane doesn’t exert enough pressure on a dome to be even noticed” (Wilson).

“It is interesting to note that German thin shell structures stood up to allied bombing in World War II better than most other structures. When a bomb hit a thin shell, it would either bounce off its tough resilient exterior, or it would puncture a hole through. Since there are no single components that carry large loads, there is nothing that can be knocked down like a beam or a column. Therefore, repair was a simple patch to cover the hole that was made when the bomb would go through” (Wilson).

Aesthetics

We now know the Monolithic Dome is strong, energy efficient, uses less material, and is cost effective. But what about aesthetics? Are domes attractive? Would you want to live in one? That is a good question. It is often said that beauty is in the eyes of the beholder.

We live in a square-building world and we are resistant to anything different. Yet, a dome is much prettier than many give it credit, and people are beginning to realize this.

A dome’s structural beauty is in its unobtrusiveness. A dome that is well built and tastefully landscaped becomes part of its surroundings. For example, a dome built on a hill blends gently into the curve of the hill. This beauty, as I said before, is very subjective. But I know that as the number of well done, attractive domes increases, the prejudices against domes will decrease.

Often I have seen portrayals of the future where people’s homes, schools, offices, shopping centers, and their whole society is in domes. I think that we are moving toward that future.

People are learning the advantages of a Monolithic thin shell concrete dome. Many people, like my grandmother, have embraced its style.

Over time, you may find yourself thinking that domes are beautiful. You may even want to buy one. And why not? We all want a building that is superior in protecting our families, saves us money, is environmentally friendly, and is beautiful.

References:

Fuller, Buckminster. Ideas and Integrities. Prentice-Hall, Inc., Englewood Cliffs, NJ 1963
Wilson, Arnold. Building Survivability. An essay compiled by Dr. Wilson for Monolithic in 1989

Note: We originally printed this article in our Fall 1999 Roundup.