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Built The Hidden Stories Behind Our Structures

Roma Agrawal

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Skyscrapers are designed to bend through a maximum of their height divided by 500 - so a 500m tower won't move more than a metre at top. But if this happens too quickly it can make you feel seasick. Engineers avoid this through the core. This can be internal, where it functions just like a tree trunk, or external, with an exoskeleton. This used on 'Gherkin' at 30 St Mary Axe, and on Center Pompidou in Paris.

Bessemer discovered that he cd make HQ steel by blowing a current of warm air through a closed furnace, without using fuel. This worked bc oxygen reacted with carbon in iron in an exothermic reaction, raising the temperature of the iron far beyond what a coal-fired furnace could.

That gave him purified iron, to which he cd add fixed amounts of carbon to produce steel of whatever quality he wanted. This was hugely popular, bc his steel was six times cheaper than anything else available at time, making it viable to use steel to make bigger items.

He quickly sold licences to mill owners all over the country, but then had to refund them when they couldn't reproduce his work. He went back to drawing board for two years, finally figuring out that (a) the failures were bc others wer using iron with a high phosphorus content, and (b) the solution was to line the furnace with lime.

Frenchman Joseph Monier figured out how to reinforce concrete with a grille of metal wires.

Reinforcing steel for towers joined into cages. "If a canary can fly out of your steel cage, the bars are too far apart. If it suffocates, they are too close together."

Self-healing concrete contains tiny capsules of calcium lactate. Inside them is a bacteria that is normally found in highly alkaline lakes near volcanoes, and which can survive without oxygen or food for at least 50 years. If a crack forms in the concrete, water seeps in and dissolves the capsules, releasing the bacteria. They feed on the capsules, forming calcite, essentially pure limestone. The calcite fills the cracks, self-repairing the structure.

In medieval Japan, human waste was a vital resource. It was loaded onto ships that carried it all round the country. There were laws which said that the feces produced by the occupants of a house belonged to the landlord (but they were allowed to keep their urine). The feces produced by 20 households was about the same as the amount of grain one person wd eat annually.

Bc waste was carefully collected, there was little contamination of water supplies. And bc they mostly drank tea, made with boiled water, Japanese communities were more sanitary and healthy than contemporary Western societies.

Thames Tideway Tunnel is an update on Bazalgette's Victorian sewers. Where B built interceptors to catch discharge from ancient streams, the TTTwill intercept B's sewers. Most of it is being built under the Thames. Aim is to reduce number of involuntary discharges of stormwater mixed with sewage from 62m tons a year to 2.4m tons. This is acceptable bc the discharges only happen in exceptionally heavy rain, and so the sewage is diluted considerably by time hits the river.

The first medieval bridges across Thames and other rivers were built by the Church, which wd build a chapel at each end for travellers to pray (and make financial offerings for safe passage).

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