Big, Bigger, Biggest: Episode 5

Tuesday 25th August 8.00pm

Continuing this week is the factual series that examines the evolution of modern engineering. This edition studies the leaps in structural technology that led to the development of the world’s largest free-standing dome – the Kyushu Oil Dome in Oita, Japan.

Home to the J League football club Oita Trinita, the Kyushu Oil Dome measures over 270 metres across and stands at 20 storeys high. Made of steel, Teflon and titanium, the roof can open at the flick of a switch, and allows sunlight into the stadium below even when closed. The pinnacle of modern structural engineering, this gargantuan dome owes its existence to nearly 2,000 years of innovation.

In 2nd-century Rome, Emperor Hadrian decided to cap a colossal temple to the gods, the Pantheon, with a 43-metre dome. However, the material with which much of Rome was built, concrete, was far too heavy for a structure of this magnitude. To prevent the dome from collapsing under its 20,000-ton weight, Roman engineers had to develop a lighter alternative. They replaced the basalt aggregate with pumice, tapered the walls of the dome, hollowed out the panels and left the apex open to the elements. To stop the bottom of the dome splaying outwards, they placed seven concrete ‘tension rings’ around the outside. “Here we have a building that’s nearly 2,000 years old and it’s still the biggest un-reinforced concrete dome in the world,” says civil engineer Ed McCann.

It was not until more than a millennium later that the Pantheon dome was bettered. The 45-metre dome atop the grand cathedral in Florence, known locally as Il Duomo, stumped engineers in the 15th century. More than a century after work on the cathedral had begun, watchmaker and Renaissance man Filippo Brunellesci came up with a design for the huge brick roof. Brunellesci employed a revolutionary method of bricklaying that allowed the dome to be constructed entirely without scaffolding. The dome took 300 men 15 years to complete – and remains to this day the largest brick dome in the world.

To expand beyond the 45-metre mark, a wholly new material was needed. At the turn of the 20th century, Col Lee Sinclair took inspiration from bridge design to come up with the roof for the West Baden hotel in Indiana. The 60-metre dome is supported by six steel bridge trusses joined together in the centre with a steel compression ring. To cope with the expansion and contraction of the metal supports, they are set on rollers. “From a hot day to a cool evening, this dome can travel an inch and three quarters,” says architect George Ridgway.

In 1965, the opening of the 196-metre Astrodome in Houston, Texas, was hailed as an architectural triumph. Designed to house the local baseball team, the stadium featured a lightweight Perspex roof. To eliminate shadows on the pitch, designers added a layer of microscopic prisms to divert the sun’s rays and diffuse the light. However, players complained of a blinding glare, which eventually led to the roof being painted over and to the development of an artificial grass substitute – Astroturf.

After fire ripped through the Bradford City ground in 1985, stadium engineers across the globe had to incorporate new safety features into their blueprints. Four years after the Bradford disaster, the 227-metre Georgia Dome in Atlanta included a high-tech ventilation system designed to dispose of smoke as soon as fire is detected.

Today, the largest dome in the world features a giant concrete tension ring, steel trusses, a glassfibre and Teflon roof to allow sunlight through and a robotic fire-fighting system. In addition to all these developments, the Oita Dome also has a fully retractable roof mounted on a complex network of trolleys, cables and rails. At the touch of a button, the two halves of the roof part like a giant eye. “The designers were trying to achieve in this space what they call a ‘second nature’ – and I think they’ve achieved it,” says structural engineer Alan Burden.

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