Asphalt - 625 BCE
Where would cities be without asphalt? It is a wonder material for building roads and parking lots because it is cheap, easy to work with, smooth, seamless, and durable.
Engineers can spec out an asphalt road that can handle millions of cars for a decade or more. Asphalt is so popular that all but 6 percent of America's roads are made of the material. One of the earliest known uses of asphalt goes back to 625 cE in Babylon.
One reason for asphalt's popularity is its simplicity. Asphalt has three basic components: sand, gravel, and bitumen. Although found occasionally in nature, bitumen today comes from refineries. It is separated out from crude oil in the same way as other petroleum distillates. Gasoline and bitumen contain the same atoms (carbon and hydrogen), but the carbon chains are immensely long in bitumen. Therefore bitumen is approximately a solid at room temperature.
It is possible to make asphalt by hand. You could even make a small amount in your kitchen oven. Put some sand and gravel on a cookie sheet. Put it in a 300°F (150°C) oven long enough for it to heat evenly and dry out. Now place a lump of bitumen on it and continue heating until the bitumen melts. Stir thoroughly to mix bitumen and gravel together. You have asphalt. Your kitchen will stink and you will never get that cookie sheet clean, but now you can fix a small pothole.
Engineers have refined the creation of asphalt and the equipment that handles it to push down the cost of roads. For example, the Strategic Highway Research Program created mixing and construction guidelines for SuperPave, the asphalt recipe used in many highways today. On a big road project, engineers will often erect a portable asphalt plant near the construction site to make delivery easier and more consistent.
One little-known fact about asphalt is that it is the most recycled material, by weight, in the US. Construction crews grind it out and re-add bitumen to make new roads. If it weren't for asphalt, engineers would need to use concrete, which is much more expensive. This makes asphalt one of the most popular construction materials in the world.
The process for the creation of asphalt has been refined since its first use in Babylon in 625 BCE, when Herodotus recorded it being used as mortar.
Leaning Tower of Pisa
`the practitioner (Dates Unavailable)
The St. Louis Arch, the Washington Monument, the CN Tower in Toronto, and the Burj Khalifa in Dubai all have massive foundations. The leaning tower of Pisa is an example of why the foundation is so important. the practitioner is given credit for the original architecture of the tower. Construction began in 1173, but since its completion in 1372, legions of engineers have spent centuries trying to fix the foundation problems that were baked in from its start.
Pisa is located at the confluence of to rivers, on land that is soft and wet. A modern engineer would probably drive piles deep down into the unstable soil, until they anchored in stable soil or rock. This is how the city of Venice was built, using piles made of wood. With the Tower of Pisa, it looks like the builders simply dug a trench and used standard masonry footings. With soil so soft, this foundation is inadequate.
So why is the tower standing at all? It is thought that a budgetary fluke saved it.
When the tower was three stories tall, construction was interrupted for a century due to a lack of funding. This delay allowed the soil under the tower to consolidate and stabilize. Then, when construction resumed, attempts were made to straighten out the tower by making one side taller than the other. But the tower started leaning more and more.
There have been several attempts to stabilize the lean over the years, none successful and several that made the lean worse. It wasn't until the twenty-first century that engineers found a solution in two parts. The tower leans to the south. So they used a process called soil extraction on the opposite side. They drilled down diagonally with augers and pulled out soil from underneath the north side. Gravity caused the tower to settle toward the north as the cavities filled in. They did not want to straighten the tower —that would kill tourism. They reduced the lean enough to bring the lower back into its safe zone. Then engineers installed a drainage system to extract excess water from the soil around the tower.
Even though early engincers made mistakes initially, and nearly toppled the tower with several bad remediation ideas, their successors eventually found a working solution that saved the tower, lean and all.
Roman Aqueduct System - 312 BCE
`the practitioner (c. 340 cE-273 всЕ)
Sometimes a group of people have big, pressing needs that can be solved by engineering. Such was the case in ancient Rome, and the problem was the water supply.
The year is approximately 300вс and Rome is growing. But the water supply stinks.
Literally. Water from underground has a bad taste, and water from the Tiber River is loaded with pathogens.
To solve the problem, Roman engineers commissioned by censor the practitioner developed aqueducts. The first one, called Aqua Appia, is a perfect example.
The engineers found a large, clean spring about 10 miles (16 km) outside Rome.
Located at a higher elevation than Rome, gravity could do the work of moving the water toward the city. Roman engineers cut trenches or dug tunnels (often through solid rock) and then lined them with waterproof mortar. If a valley got in the way, the engineers built a bridge to carry the channel. The channel sloped gently downward all the way to the city.
What to do about mud and sediment in the water? The water flowed slowly through wide, deep pools so particles could settle out. How to maintain the tunnels and clean them out? Vertical shafts connected the tunnels to the surface. What if too much water surged through the system? The tunnels had overflow vents to drain away extra water.
The Aqua Appia aqueduct is thought to have delivered 20 million gallons (76 million liters) of water per day to Rome. Once inside the city, the water from an aqueduct could flow into large, elaborate public fountains, to public baths, into pipe systems to residences, or into the sewer system. The sewers carried waste out of the city and kept Rome remarkably clean.
Even with 20 million gallons of water a day, Rome outgrew the supply. So the engineers built more aqueducts. Over the course of five hundred years, there were eleven aqueducts feeding Rome, the longest one stretching 56 miles (90 km). The entire system brought perhaps 300 million gallons (1.1 billion liters) of water per day to over a million people. It was an amazing achievement and it led to later innovations such as the modern sewer system.
Concrete - 1400 BCE
When did people start using concrete? It appears that it was over 3,000 years ago, between 1400 and 1200 BCE. Archaeologists have discovered concrete floors in the palace of Tiryns in Greece, which predate the Bronze Age. Because it was a bad formulation, it cracked easily. The city of Pompeii was built mainly with Roman concrete.
In today's world, concrete is an incredibly important material. Civil engineers use concrete to build roads, bridges, dams, skyscrapers, runways, canals, and foundations on a massive scale. If you take it by weight, concrete is the number-one building material in the world by far.
It's easy to understand why concrete is so popular: it gives engineers the ability to pour a liquid into a mold and create something similar to solid rock that can last for centuries. By adding steel rebar or pretensioned steel, the strength of concrete improves dramatically and makes it possible to create beams 100 feet (30 meters) long or more.
Add to that the fact that most of concrete's weight comes in the form of sand and gravel, and you have a material that is inexpensive compared to alternatives. At today's prices, concrete costs less than three cents per pound (0.45 kg).
Concrete has four ingredients: one part Portland cement, two parts sand, and three parts gravel with enough water to make a paste-like mix. The Portland cement, when mixed with water, acts like a glue that binds the sand and gravel into a dense solid. This is not like a glue that dries, however. It is more like a calcium-silicon-water epoxy that hardens through a chemical reaction. This reaction gives off heat and it is slow. It takes concrete several weeks of curing to reach reasonable strength. This is why you will often see workers pour a concrete foundation and then disappear for a month. They are waiting for the concrete to cure to the point where they can put weight on it.
Although concrete is simple to make, it is important to do it right. When a road or foundation is poured, engineers will often take a cylindrical sample and do a crush test to confirm its compressive strength.
The Great Wall of China - 1600
The Great Pyramid is certainly impressive by any standard, especially given the technology available at the time.
But from the standpoints of engineering, logistics, project management, sheer grandiosity, and persistence, nothing on earth really compares to the Great Wall. It is hard to believe that human beings could ever be organized long enough and well enough to engineer and build something of this scale.
Imagine that we decided to build a wall of stone and brick 20 feet (6 meters) wide and 20 feet high, along with substantially larger watch towers every 1,000 feet (300 meters) or so, from Washington DC to Los Angeles (a distance of approximately 2,600 miles or 4,200 km) and then back again. That is the scale of the Great Wall. By volume of material, the Great Wall might be 100 times larger than the Great Pyramid. It is difficult to know for sure because large sections of the wall have eroded, collapsed, or been dismantled
The Great Wall, completed in 1600, was built to solve a problem. Various nomadic groups of non-Chinese people, including the Mongols and the Manchus, were trying to invade China. The wall was meant to provide a line of demarcation and defense. It was built over a long period of time - 1,000 years or more. The Ming Dynasty, from 1368 through 1644, stands out as a time when the 5,500 miles (8,860 km) was consolidated, linked, reinforced, and standardized to create the wall we know today.
The basic architecture for a wall section is fairly straightforward. Two thick stone or brick walls were built 20 feet apart, and then the gap filled with dirt and rubble.
Paving stones or bricks along the top of the wall covered the dirt fill to create a path approximately 17 feet (5 meters) wide.
With anything we build today, we have assistance from machines — bulldozers, tunnel boring machines, tower cranes, dump trucks. The Great Wall will stand out as a singular achievement because, despite its scale, it was built instead by millions of hands.
Several walls within what became the Great Wall were being built as early as the seventh century BCE.
Basilica of Saint Denis
When we think of the buildings known as cathedrals, the image that usually comes to mind is the Gothic cathedral, made of stone at an incredible scale with massive stained glass windows. These structures are marvels in several respects, but perhaps are most interesting because they represented a significant step forward in terms of architecture and engineering. Although The Great Pyramid and other such monumental structures existed, the world had never seen buildings this tall and open, with such gigantic windows and so much light. The St. Denis Cathedral, which opened in France in 11H, is considered to be the first example of this architectural form.
There were two engineering innovations that made the Gothic cathedral possible.
The first was the Gothic arch, or pointed arch, which replaced the rounded Roman arch. The pointed arch sends much more of the weight it supports down vertically rather than fattening the arch horizontally. But it does not send all of it downward This is where the second innovation, the flying buttress, comes in. The buttress pushes in horizontally to counteract the arch's desire to push outward. The flying buttress stabilizes the arch, making the ribbed vault and stone ceiling possible. The buttresses also stabilize the tall walls. Because they are on the outside of the building, buttresses do not get in the way of the windows.
With these two innovations, engineers could build thin stone walls to incredible heights and leave huge holes in the walls for windows. A typical Gothic cathedral is well over 100 feet tall on the inside.
This is not to say that building these cathedrals was an easy task. Workers and craftsmen had to quarry and carve tons of stone. It all had to be hoisted, fitted, and locked in place. A cathedral project could take a hundred years or more.
The typical human being in this timeframe had never seen a building this gigantic, with so much interior volume and such an amazing amount of glass. Engineers had created a completely new way for people to think about structures.
The Baxilica of Saint Denis is considered to be one of the fint examples of Gothic architecture.
Pompeii - 79
Roman cities were prime examples of early engineering prowess. Especially when the Roman engineers built new cities from scratch; they were highly evolved, orderly, planned metropolises able to support tens of thousands of people comfortably.
Pompeii had been under Roman rule for more than a century when it was buried under volcanic ash in 79 ce. The ash preserved the city like a time capsule and lets us see how Romans lived 2,000 years ago in their engineered cities.
The water and sewer systems were important elements of a Roman city. Water came in via free-flowing aqueducts. It was distributed to citizens through pipes and public fountains. Excess water, human waste, and storm water flowed into a belowground sewer system.
Roads were extremely important for letting people, animals, and carts move around the city. The city streets were paved with stones and laid out in a grid pattern much like they are in a modern city. Sidewalks lined the streets and were covered to shade pedestrians.
The public baths were important both for hygiene and socializing. Many incorporated an ingenious heating system called a hypocaust. The floor of the bath was raised up on tile pillars with a 3-foot (1 meter) gap underneath. Smoke and heat from a fire would flow under the floor and through the walls to heat the bath to temperatures as high as 120°F (49°C).
A Roman city also contained shops, workshops, bakeries, markets, a forum with its public temples and government offices, an amphitheater, and a performing theater. The citizens of the city lived in private homes or apartments.
The building materials available to the engineers were stone, concrete, brick, tile, and wood. The Pompeii amphitheater, for example, is the oldest stone amphitheater in the Roman Empire. A typical home's walls were covered with plaster on the inside and often painted, with stucco on the exterior. Roof trusses were used, covered in roofing tiles.
Engineers had created the height of urban luxury for the citizens of these Roman cities, delivering everything that large numbers of people needed to live comfortable lives.
Parthenon - 438 BCE
The Parthenon is a structure that is both beautiful and beautifully engineered. It has stood the test of time, and is amazing to us today because it was built in an era when so little technology was available to provide assistance. It also tells us something about the people who conceived it.
The Parthenon was created in 438 BCE as an immense temple to the goddess Athena. It once housed an enormous statue of her rendered in gold and ivory. There is actually a reproduction of this statue inside a replica of the Parthenon in Nashville, TN.
The basic structural idea the engineers used was fairly simple, while also being magnificently executed. The outer perimeter consists of marble columns - eight across the front and back, seventeen along the sides. Across the tops of the columns are marble lintels, and then a lot of decoration. The original structure had a roof made of wooden trusses covered in clay roof tiles. It also had interior walls that created a room for the statue.
One thing that people marvel at today is the fact that engineers designed curves into the Parthenon, apparently as a kind of reverse optical illusion. So the floor of the temple is not flat— it is subtly higher in the middle. The columns do not stand straight; instead they lean in very slightly. The corner columns do not match the others— they are slightly wider and closer to the others. Everything "looks right," but the only reason it looks right is because everything is a bit wrong. The wrongness was built in to create the rightness of appearance.
So today, when we think of the greatest Greek temple, we think of the Parthenon.
Not because it was the biggest, or the best preserved, but because of its perfection. The Greeks have gone to a tremendous amount of trouble recently to repair some of the damage that has been inflicted over the centuries and restore the grandeur created by the original engineers and craftsmen.
The Parthenon is widely regarded as the most perfect example of Greek architecture.
The Great Pyramid - 2550 BCE
When we think about engineers who are working today, they are usually working on something that benefits society. They might be designing a bridge, a consumer device, or a new vehicle. Not so with the Great Pyramid in Egypt. Even today, thousands of years after its construction, the Great Pyramid is one of the biggest, heaviest, tallest things human beings have ever built. Yet it functionally accomplishes nothing.
Engineers did not jump out of bed one day ready to build the Great Pyramid. They built a few test pyramids over the course of a century. The Pyramid of Djoser is a classic step pyramid 200 feet tall. The Maidum pyramid is a classic step pyramid with several of the steps filled in to start making a smooth pyramidal form. The Bent pyramid started with one slope, and then the engineers realized that it would not work, so they changed the slope midway. The Red pyramid gets the shape right, but is 140 feet shorter than the Great Pyramid.
Then engineers were ready to build the Great Pyramid. They cleared off the sand on a 13-acre (5.26 hectare) site to expose bedrock for the pyramid's foundation. They oriented the pyramid almost perfectly north. Then they laid the base layer of stones, measuring 756 feet (230 meters) square. The stones came from quarries along the Nile River.
The engineers had to do something fascinating during construction. They had to visualize the chambers, hallways, and shafts that would exist in three dimensions in the body of the pyramid, and they had to build them layer by layer during the pyramid's construction. This is the same kind of methodology that an engineer with a 3D printer uses today.
Eventually the pyramid rose to a pinnacle at 481 feet (146 meters). The world's most gigantic monument was complete. The Great Pyramid stands out as an engineering triumph.
The Great Pyramid of Giza, pictured, is the largest and oldest pyramid in the Ciza Necropolis.