The history of engineering revolutions Part 2
But perhaps the most common type of arch in our architecture is the dome arch, turned around its own vertical axis by 180 degrees. It's good to show the example of the Pantheon, which was held, probably the longest record in the history of mankind: the passage of a width of 43 meters nobody could beat for 1,300 years until, until it was built the Cathedral of Santa Maria del Fiore.
And now let us think, due to what the Romans managed to achieve this. Stone is heavy stuff. When we build from it vaulted design and deliberately prolonged the span is proportionally increased weight. Sooner or later we reach the limit at which the structure collapses under its own weight. So what is the Romans came up with to solve this problem?
And here we see two innovations. First, it is believed that the Romans invented concrete, which is now called Roman. Concrete, like stone, is quite heavy. But it can be easy if instead of sand and gravel to use another filler, porous pumice. It turns out something like the well known blocks. But there is another problem, this concrete will have great bearing capacity. Builders have solved this problem by doing the following engineering revolution, which is associated with the appearance of the frame.
It turns out that already in the Pantheon we can find a prototype of the framework: radial ribs, which are connected together rings and the intervening arches. This is not the usual rectangular frame, and the frame is very complex shapes. The space between the stone detail Stripping thereby filled with lightweight concrete, which in this case takes on the role of a cladding material. The concrete carries no load, it assumes the frame only.
To use the framework EN masse for the first time in the construction of Gothic churches. For Gothic is characterized by the up. The massive walls of the Pantheon quenched the horizontal thrust of the great dome. But the Gothic churches much higher, and in this case to make the massive wall is extremely inefficient material flow is too large. Not to mention the fact that in the middle ages was lost the secret of Roman concrete and used lime sand mortar is quite low binding ability. Walls if they are very massive, could just collapse under its own weight.
But what affects us most when we enter a Gothic Church? This is a neat pattern on the ceiling, called ribs. Architect, being a big fan of Gothic, on this occasion wrote: "the Gothic, in my opinion, the most truthful, the most honest style in architecture; it does not hide your design behind the decoration it brings them to such a degree of perfection that they are perceived as an element of decor". Indeed, the rib is naked, no closed cage. But it is so beautiful that seems to us to be a decoration of the temple. This is a weighty argument in favor of what often becomes the primary source of engineering architecture.
And yet, before entering the Gothic Church, we see a fish skeleton from the columns. They are called buttresses, or, in translation into "counter force". That is, even their name suggests that they are not an architectural element, and engineering. And it is needed in order to compensate for the horizontal spacers. Thin walls under the arch might collapse. But the load is not transmitted to the walls, and the small arches (were added), which, in turn, transmits it to the reference column.
These poles are often heavier than the wall itself. And even, it would seem a completely decorative item as a hip tower (the pinnacle), has absolutely constructive purpose. Sometimes it was made of stone, and sometimes additionally have heavier cast iron liners. And it gives us a clue: if the pinnacles weighting, so the task was to make a buttress heavier and thus more stable on the same horizontal thrust.
Although the Gothic and achieved a lot in terms of frame based structures, and delicacy, to throw a large slab of stone was still difficult. So the next revolutionary step is associated with a new design and new material, which unlike the stone already worked well in bending. And this iron. It appeared, of course, a very long time, but to obtain it in large quantities for a long time could not.
As for the construction it is necessary very much this is not chain mail to do and not a sword to be forged. The situation with the production of iron was adjusted only in the second half of the XVIII century; then began its use in architecture. The oldest extant example of the so called cast iron style it's cast Iron bridge in England, built in 80 ies of the XVIII century.
With all its advantages regarding stone, cast iron still bad bends and stretches, so is used mainly for the construction of columns and arches. The top of the cast iron architecture is the construction of the world industrial exhibition in 1851 the Crystal Palace. The world Expo is a very good engine engineering progress, because they not only that was a fair engineering advances, they also demanded the building of enormous pavilions with giant spans.
In the mid nineteenth century to replace the cast iron gradually comes steel. From cast iron it is smaller in carbon content, so has elasticity and flexibility, works better in bending and stretching. So begins the era of skyscrapers.