The first houses humans built after getting out of caves were in the shape of a tent. The basis for this tent was a Λ-shaped frame borrowed from nature. It was not comfortable and severely limited any possibilities for further development, allowing virtually no growth in breadth and height.
That is why what could be called the first engineering revolution was due to the emergence of a П-shaped frame – the so-called post-and-beam structure. This revolution has also proved to be the most ingrained, because up to this day 99% of all buildings are constructed using some modification of the post-and-beam structure. But we mostly associate it with classical antiquity.
Where do you think the antique colonnade rhythm comes from? Why are the columns this dense, not twice or ten times sparser? The main reason is that the beams are made of stone. Look: if we take a plank, place its ends on two supports and stand on it, it will bend. While stone doesn’t take bending moment well, it breaks instead. The distance between columns that a marble beam is guaranteed to withstand is three to four meters. And here is where the colonnade rhythm comes from, which the Greeks managed to spread so well that it is now considered to be a classical, by-the-book rhythm. But I think that all these proportions are caused by engineering reasons. Besides, Greeks are well-known for their proclivity for beautiful things. Which is why they always made the places of connection of columns and beams look complete, trying to put them into some shape. Here is where the famous antique order system was born, which was nothing but an attempt to artistically shape the place where the beam rests on the column. But we must always make allowance for the fact that aesthetics can be different at different times. While now we are used to a certain rectangular section of beams and columns, at that time it could seem a bit weird.
Stonehenge, one of the earliest examples of a post-and-beam structure.
2Parthenon, an architectural monument built in 447 BC and a bright illustration of a classical colonnade.
As I already said, the post-and-beam system has one major drawback – stone works in bending and hence limits the span length. This is why the following revolution was the emergence of such a structure that helped engineers to make stone operate into the only effective type of load for it – compression. And such a structure is called an arch.
The Arch of Constantine, a triple-span arch located in Rome between the Colosseum and the Palatine Hill on the ancient Via Triumphalis. It was built in 315 AD.
Arches are believed to have been invented in Ancient Rome. They may have been known before that as well, in Ancient Mesopotamia, but it were the Romans who were the best distributors. They spread the arch all over the world and thus secured the right to be called its inventors. And that is why it is often called Roman Arch.
The stones used in arches are very small, so they don’t take bending moment but press against each other and shrink instead. In the end stone will crack anyway but it can still withstand quite a heavy load. However, as it is known, nothing comes without a cost. In this case, we eliminate bending at the cost of having horizontal thrust force in heel joints. One could even say that the whole history of engineering, from the classical era to at least the Middle Ages or maybe even longer, is the history of struggling against horizontal thrust.
The Pont du Gard, the highest surviving Ancient Roman aqueduct. It connects the two banks of the Gardon River in France.
Multiple arches were used by Romans to build bridges and aqueducts. By the way, to see an aqueduct you don’t have to visit Ancient Rome. They are found in other cities too. There is one in Moscow, for instance, called Rostokino Aqueduct. Also, on closer examination of many famous buildings it appears that they are actually merely sets of arches. For instance, the Colosseum is basically several arcades placed on top of each other and several rowlock walls consisting of arches and also placed on top of each other.
But most of us are more used to seeing vaults rather than arches in pure form. Any vaults used for any parts of churches up to the 17th century are based on an arch. The simplest type vault is called flat-arched vault or barrel vault. It looks like half of a cylinder but in fact is a heavily elongated arch. If we take two halves of a cylinder, cut through them and take out the central lobes we will get a groin vault. If we cut through two half-cylinders, cut off the excessive matter but leave the central lobes (which basically are segments of the intersected cylinders), we will get a cloister vault. Cloister vaults are typical of Russian architecture. They can be seen in chambers of the House of Romanov and palaces of the British Court. Barrel vaults were most often used when building basements, while a possible example of a groin vault would be the Golden Entrance Hall to the Palace of the Facets in Kremlin.
The interior of the Pantheon in Rome. It was built in 126 BC under the rule of Emperor Hadrian.
But probably the most widespread type of a vault in Russian architecture is a dome – an arch turned 180 degrees around its vertical axis. This can be shown on the example of the Pantheon that held possibly the longest world record in the history of humankind: no one could surpass the 43 meters long arch span for 1300 years – till that moment when the Dome of Florence Cathedral was built.
And now let’s think about how the Romans were able to achieve this. Stone is a heavy material. When we build a vault structure for it and intentionally expand the span, the weight also increases in proportion. Sooner or later we reach the limit beyond which the whole structure will collapse under its own weight. So what did the Romans come up with to solve this problem?
Here we see two innovations at once. Firstly, it is believed that the Romans invented the type of concrete that today is called Roman concrete. Like stone, concrete is pretty heavy. But it can also be light, if instead of the sand-and-gravel mix you use a different filler – porous pumice. You get something like foam concrete blocks. But at the same time another problem appears: such concrete will not have a high load-bearing capacity. But the construction engineers solved this problem too, thus accomplishing another engineering revolution that is the creation of a framework. As it happens, as early as in the Pantheon we see some kind of a prototypical framework: radial stiffening ribs joined together by rings and arches between them. It is not an ordinary rectangular framework but a framework of a very complex shape. The space between the stone parts, or spandrels, is filled with the same light concrete that in this case assumes the role of merely an enclosing material. This concrete does not bear any load, only the framework does.
The mass use of framework began with the construction of Gothic cathedrals. The Gothic style has a characteristic feature of the verticality effect. Massive walls of the Pantheon cancel out the horizontal thrust of the huge dome. But Gothic cathedrals are much higher, and in this case building massive walls is extremely disadvantageous – the material consumption will be too big. Not to mention the fact that in the Middle Ages the secret of Roman concrete was lost, which is why they used sand-lime mortar with a very low binding capacity. If the walls were massive, they could simply collapse under their own weight.
But what does strike us most of all when we enter a Gothic cathedral? It’s the exquisite patterns on the ceiling, called arch ribs. A big admirer of the Gothic style architect Aleksandr Kuznetsov wrote: “The Gothic style, in my opinion, is the most truthful, the most honest style in architecture; it does not hide its structures behind ornaments and decorations, but instead brings them to such a level of perfection that they themselves are perceived as decorative elements”. And indeed, the arch ribs are basically bare, unconcealed framework. But they are so beautiful that they seem like decoration to us. This is a convincing argument in favor of the theory that engineering is the mother of architecture.
Milan Cathedral, built from white marble in the Flamboyant style. The construction began in 1386 but ended only in the early 19th century, when on Napoleon’s orders the decoration of the facade was completed. Some finishing touches, however, were being put up until 1965.
Also, right before entering a Gothic cathedral, we see a fish skeleton made of columns. These are called buttresses or counterforts – because they literally counter the force. So, even the name tells us they are not architectural elements but engineering ones. And they are needed to compensate for horizontal thrusts. Thin walls could collapse under the weight of the vault. But the load is not transmitted to the walls but to a small arch buttress (or flying buttress) which in its turn transmits it to the support pier. These piers are often even more formidable than the wall itself.
And even such a seemingly decorative element as a tent-roofed tower (pinnacle) has a structural purpose. Sometimes this tower would be made of stone and sometimes it would be made heavier with cast iron inserts. And this gives us a hint: if pinnacles were specifically made heavier then the goal was to make the counterfort heavier and hence more stable to the horizontal thrust.
A cast iron bridge in England built in the 1780s.
Although Gothic architecture achieved a lot in terms of framing and open work, it was still difficult to make large stone slabs. That is why the next revolutionary step was not the emergence of a new structure but the emergence of a new material which, contrary to stone, worked in bending very well. And that material is iron. Of course, it appeared a very long time ago, but for centuries nobody could produce a sufficient amount of it. And you need quite a lot of it for construction – it isn’t as easy as making a chainmail and forging a sword. This iron production shortage situation only improved in the second half of the 18th century; at the same time they began using iron in architecture. The oldest surviving example of the so-called cast iron style is the Iron Bridge in England, built in the 1780s.
With all its advantages over stone, cast iron still doesn’t bend and stretch well, which is why it is mostly used to build columns and arches. The peak of cast iron architecture was the construction of the Crystal Palace built to house the Great Exhibition of 1851. World’s fairs in general were a great engine of progress, because not only were they showcases for engineering achievements but they also required construction of large pavilions with giant arch spans.
In the middle of the 19th century cast iron was gradually replaced with steel. Steel is different from cast iron in that it has lower carbon content and hence is more elastic and works better in bending and tension. This is how the skyscrapers era began. But the necessary momentum for this era was not only the emergence of industrial steel production methods but also the emergence of a rolled section – an H-beam placed on the side. This is important because any box structure is quite strong, its strength being commensurable with that of a one-piece structure but at the same time a box structure is much lighter.
The first skyscraper appeared in Chicago in 1886. It had a completely steel load-bearing frame and it is this fact and not the height of the building (which wasn’t very high, by the way, just 12 stories) enables us to call it a skyscraper.
The next engineering revolution was the creation of a truss, an engineering structure that remains stable after substituting its rigid joints with flexible pin joints. The simplest example of a stable shape is a triangle.
A truss bridge across the Vistula River in Poland.
Trusses begin to gain widespread in the 19th century, which is facilitated by the railroad transportation growth. It is trusses that become the primary structural component of newly built bridges and trainsheds. In Russia the first wooden truss bridge, the Verebyinsky Bridge, was built during the St. Petersburg-Moscow railroad construction in the 1840s (the first Russian long-distance railroad). However, the truss system for that bridge was designed by American engineer William Howe. But the most famous truss structure in the world is, of course, the Eiffel Tower.
From around the middle of the 19th century structural analysis becomes regular practice. And one of the harbingers of such analysis is also associated with the Verebyinsky Bridge. Metallic tie rods (tension bars) in Howe trusses had the same size section. But young Russian engineer Dmitrii Zhuravskii who participated in the construction of that railroad noticed that the tension inside the bars is different, which means they can be made with different size section, and that will allow saving some material. The young engineer’s words were left unattended, so he performed possibly one of the greatest experiments in the history of construction. He created a scaled-down model of a bridge made of wooden battens, and used strings instead of tie rods. Then he loaded his bridge proportionally, made a fiddle bow and ran it over the strings. As you can guess, the strings sounded different in pitch at different places. Thus he proved that they all have different tension and hence they can and must be made of different thickness. Such trusses were called the Howe-Zhuravskii trusses. At least before the 1870s they were widely used all over Europe. Only completely steel trusses were able to replace them.
The Union Bridge, the oldest surviving suspension bridge in the world. It was built in 1820 across the border between England and Scotland.
But, as good as trusses were, different elements operate into different types of loads: some stretch, others compress or bend. But the majority of the components work in compression. Any engineer will tell you that steel works in tension much better because the next revolution is the emergence of structures that make steel stretch and expand. We’re talking about hanging and suspended structures that were mainly implemented in the construction of bridges. Barring suspension bridges made of lianas that were used in Central America and South-East Asia for centuries, the first suspension bridge was arguably the bridge built in the late 18th century in Pennsylvania by Irish engineer James Finley. This bridge has not survived but it can be used as an example to see how suspension bridges work.
Instead of placing the span on top of a steel arch that works in compression we hang it on chains. The primary chain is thrown over piers (posts) and fixed in the ground with strong anchor blocks. The piers in such case are under a light compression load coming from the chain’s weight; the main load is put on the chain and anchor blocks.
One of the most famous suspension bridges in the world is the Golden Gate Bridge in San Francisco. While the Akashi Kaikyō Bridge is the record holder: it has the largest span in the world – almost two kilometers long.
The Akashi Kaikyō Bridge, a suspension bridge in Japan. This bridge is the longest suspension bridge in the world: its full length is 3911 m, its central span is 1991 m long and the height of its piers is 298 m.
In Moscow there is only one suspension bridge – the Krymsky Bridge. But it is not very plausible in terms of technical benefit. As its span is only 135 meters long, an arch would also withhold that easily. Such, for instance, is the case of the neighboring Bolshoy Kamenny Bridge and Bolshoy Moskvoretsky Bridge. At some point the Krymsky Bridge was the world’s most dubious record holder among bridges – it had the biggest metal consumption per unit of surface. But at the same time it looked great and deservedly became one of the symbols of Moscow.
By the late 19th century another type of suspension bridges appears – cable-stayed bridges. As opposed to ordinary suspension bridges, these have cables (stays) stretching directly to the pier, which is why the pier takes the entire compression load. The cable-stayed bridge that has the largest span in the world is the Russky Bridge in Vladivostok, with an 1104 meters long span. The highest bridge in the world and also one that is probably eligible for the “most beautiful bridge in the world” title is also a cable-stayed bridge. It is the Millau Viaduct in France. When you ride across that bridge you see clouds below you. The highest pier of this bridge is 350 meters high. This means that it is higher than the Eiffel Tower and even than the highest building in Europe – the Mercury City Tower in Moscow (343 meters).
The cable-stayed Millau Viaduct in France, the highest traffic-carrying bridge in the world. One of its supports is 341 meters high – slightly higher than the Eiffel Tower and only 40 meters lower than the Empire State Building in New York City.
There’s no denying it: steel is a great material. But even steel has a few disadvantages. Firstly, steel rusts; secondly, it melts. If the framework starts softening upon exposure to high temperature, being at the same time subjected to immense load from upper stories, it could lead to an accident. But there is also the third drawback: steel is quite expensive. This is why we will take a look at the next revolution: it happened when another material appeared – the one that rids steel of all its drawbacks in one sweep. This material is reinforced concrete that combines all the best qualities of steel and stone (after all, concrete is basically artificial stone). Here is how it works. The bottom layers of a horizontal beam always stretch while the upper ones compress. Let’s remember that it is steel that works well in tension so we have to place the bigger part of the reinforcement into the bottom part of the beam. While stone works well in compression. So, we place more concrete into the upper part of the beam’s cross-section. In addition to that the metal gets protected against corrosion and fire, while its consumption becomes relatively low.
The first building made of full-fledged reinforced concrete appeared in France in 1853. It was built by François Coignet. But he did not patent the technology or continue its development. For that reason many people associate the invention of reinforced concrete with the name of French gardener Joseph Monier. He used to sell potted plants, and their pots would often break. And he came up with a solution to that problem. He made a pot out of a steel mesh and coated it with sand-cement mortar. In 1867 he patented this technology. Then he also patented everything else that could be made of reinforced concrete: bridges, floorings, staircases, etc. Later all his patents were bought by Germans. It was the Germans who laid the foundations of the science behind reinforced concrete and facilitated its widespread in the world.
Finally, the last revolution was the emergence of new structures that taught concrete to take all kinds of shapes thus accurately following, firstly, the architect’s plan and giving him many additional tools and, secondly, the engineer’s plan, because concrete, due to its flexibility, could take the exact shapes that are more reasonable in terms of distributing the load in the structure. These structures are called reinforced concrete envelopes or concrete shells. The trendsetter here was Italian engineer Pier Luigi Nervi who built a lot of these envelopes all over the world.
An envelope is a very thin coating, which can be illustrated on the example of a chicken egg. The ratio of shell thickness to egg diameter is 1:133. Imagine that this egg is as big as the Pantheon. Then its shell will be 12 times thinner than the Pantheon’s dome, in spite of all the structural design efficiency. That is, in the 2nd century AD, when the Pantheon was built, nature was still way ahead of engineering. And now let’s take a look at the Paris exhibition hall built by Pier Nervi in 1958. Just imagine this: with the span width of 220 meters (commensurable to the Luzhniki Stadium in Moscow) it is covered with an envelope which is only 12 centimeters thick. While a similar size egg would have a two meters thick shell!
The Paris exhibition hall designed by Pier Luigi Nervi, an example of using a reinforced concrete envelope.
In the 1960s-70s architects return to the use of steel. German architect Frei Otto becomes one of the first people to create a net-line coating made of steel and glass. I think that most professionals at some point of their career start asking themselves questions like: “Who are we? Where did we come from and where are we going?” And apparently Frei Otto thought to himself: “Can it be true that I was the first who came up with these steel and glass-metal envelopes?” So he started looking for people who did that before him, and that’s how he found Vladimir Shukhov’s works. Shukhov had been long forgotten by that time. He was somewhat known in Russia as the creator of hyperboloid structures but nobody remembered his unique net-line coatings. And it was in fact Shukhov who first had the idea to use steel in tension not only in bridges but also in coatings of buildings. He hit upon this idea as early as in 1894. For the All-Russia Industrial and Art Exhibition of 1896 in Nizhniy Novgorod Shukhov constructed eight pavilions with the first ever coverings in the form of net-line coatings.
These membrane envelopes became one of the last trends in engineering and construction design, and today their use has become a regular practice in European, North American and Japanese architecture. Membranes are envelopes that have both load-bearing and enclosing functions. That is, they both withstand their own weight and protect the structure from rain and snow. These are very thin envelopes usually made of synthetic fabric – quite thick compared to regular fabric but thin compared to reinforced concrete. The membranes were also Vladimir Shukhov’s invention, and here’s what’s so great about them. A net-line coating usually has a load-bearing net part and the enclosing part – roofing iron or glass. So Shukhov thought: wouldn’t it be possible to manufacture a coating out of roofing iron so that it could withstand the load? As a result he built a rotunda pavilion with a suspended membrane 25 meters in diameter for the same Nizhniy Novgorod exhibition. The membrane was made of roofing iron and was actually capable of bearing the load.
The Millennium Dome in London constructed by Richard Rogers was already created using the membrane enveloping technology.
What the next revolution is going to be, I don’t know. But I feel that the fruitful journey we’ve seen in the previous revolution is the journey of retrospect, of learning from the past. Study the past, and you’ll be ready for the future!