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The history of engineering revolutions Part 3

But the impetus to her becoming not only the emergence of methods for the industrial production of steel, but the appearance of the rolling profile I beam in the form of the letter "H" laid on its side. This is important because any box like structure has great strength, comparable to the strength of a solid structure, but it is much easier for her.

The first skyscraper appears in Chicago in 1886. It has the entire steel framing, and it is this fact, not the height of the building (which, incidentally, was small only 12 floors) allows you to call it a skyscraper.

The building insurance company in Chicago, built in 1885, is considered the world's first skyscraper. The original had only 10 floors and a height of 42 m. Later, in 1891, was built on two more floors and building height increased to 54.9 m.

The next engineering revolution produces farm (from Latin firmus a "durable") construction, remaining geometrically unchanged after replacing it the hard nodes of the hinge. The simplest example of invariant figure is a triangle.

Actively spread the farm starting in the XIX century, thanks to the development of railway transport. What farms are the main structural component of construction of bridges and station landing. In our country the first wooden truss bridge was built during the construction of railway (our first long railway) in the 40 of the XIX century. However, the system of farms was developed by an American engineer Gau. But the most famous truss was, of course, the Eiffel tower.

From the middle of XIX century in the broad practice of structural analysis. And one of the first signs in the calculations was connected with our bridge. Metal bands (tension rods) in the farm system, Gau had the same cross section.

To the young engineer was not considered important, and then he was probably one of the most beautiful experiments in the history of the construction. He made a scale model of the bridge of wooden slats and strands had replaced the strings. He then proportionally loaded my bridge, made a bow and held it on the strings. As you might guess, strings in different places gave different pitch.

Thus he proved that in them there is different voltage, and so they can and should do different thickness. Such a farm is called "farm". At least up to 70 years it was used throughout Europe. To push them were only able to entire steel truss.

But in the farms, however good they may be, different elements work for different types of loads: some are stretched, others compressed, the third bend. And a major percentage of elements of the work is still in compression. Steel, as will tell you of any engineer, tensile works much better, so the next revolution is the emergence of structures in which steel is forced to stretch. Is suspended and suspension structures, which were implemented mainly in bridges.

If you do not take into account the hanging bridges of vines, which have long been intertwined somewhere in Central America and Southeast Asia, the first suspension bridge can be considered a bridge built in the late XVIII century in Pennsylvania, the English engineer James Finley. This bridge has not survived to our days, but for example, it is possible to consider, how do suspension bridges work.

Instead of resting the superstructure on working in compression, steel arch, we hung him on chains. The main chain is thrown through the pylons (pillars) and secured in the ground with a powerful anchor blocks and anchors. The pylons have a small load in compression from the weight of chains; but the main burden falls on the chain and anchor blocks.

One of the most famous suspension bridges in the world are the Golden Gate in San Francisco. But the Akashi bridge in Japan holds the record: he's got the largest main span in the world nearly two miles.

Akashi Kaikyo bridge in Japan. The bridge is the longest suspension bridge in the world: its total length is 3911 m, the Central span has a length of 1991 m, pylon height is 298 m.

In the late nineteenth century, there is another kind of suspension bridges cable stayed. They have, in contrast to the conventional suspension bridge, the cables (cables) are drawn directly to the pole, and therefore it accounts for all the compressive load.

The highest bridge in the world, and at the same time, probably applying for the right to be called one of the most beautiful, the same cable. This is the Millau viaduct in France. When you go on the bridge, the clouds are below you. It is the highest pylon has a height of 350 meters. That is, he is taller than the Eiffel tower and even than the highest modern building in Europe, mercury city tower (343 meters).

The cable stayed Millau viaduct in France, the world's tallest vehicle bridge. One of its pillars has a height of 341 meters slightly higher than the Eiffel tower and only 40 meters lower than the Empire state building in New York.