The Troll A - A Record Breaking Gas Platform

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The Troll A - A Record Breaking Gas Platform

Rising out of the North Sea where it takes a lashing from some of the roughest waters on the planet, the Troll A platform is one of the largest and most complex engineering projects in the world and, when it was towed into place in 1996, became the largest structure ever to be made and stands in the Guinness Book of Records as the largest offshore gas platform.

For any fan of engineering feats, the Troll A platform is something to admire. Even from afar it's scale is jaw-dropping. This natural gas platform in the Troll gas field has an overall height of 472 metres. Put into context; that's 148 metres taller than the Eiffel Tower and some sixty metres taller than the Word Trade Centre stood before it was destroyed. The construction involved 100,000 tonnes of steel - enough for 15 Eiffel Towers - and 245,000m3 of concrete, that's the equivalent of 215,000 foundations for usual houses.

Of its 472 metres, the platform stands 303 metres below the surface of the sea. As each of the four legs of the platform are subjected to huge amounts of pressure - especially at the bottom - the construction method had to ensure that the concrete would be flawless, if it wasn't the consequences would be disastrous. Accordingly, the legs are made up of over 1 metre-thick steel reinforced slip-formed concrete. This means that the concrete was formed in one continuous pour to mean there was no seams or cracks and each of the legs is a mathematically joined composite of conical cylinders flaring out to larger dimensions at the top and bottom.

Each of the Troll A's mammoth-like legs are joined by a reinforced concrete box interconnecting the legs. This "chord shortener" serves as vital a purpose as the thickness and reinforcement of the concrete. As the Troll A is constantly hit by waves of varying size and force it's structure is subjected to resonance. Sustained exposure to a certain resonance can crumble even the thickest of structures, as evinced by the collapse of the Tacoma Narrows Bridge in Washington in 1940. The concrete box that connects the Troll A's legs dampens out the resonances by returning the legs' natural frequencies.

A structure worthy of admiration, the Troll A was built by Norwegian contractors with work commencing on the base in July 1991. The deck was constructed separately and were joined in 1995 when the base was partially submerged - the only way to get the deck atop the giant legs. In an operation that took seven days, the platform was towed more than 200 kilometers out to the Troll field before being fixed to the sea floor with each leg using a group of 40 metre tall vacuum-anchors to keep it in place.

The purpose of all this awe-inspiring engineering? Natural gas. The gas rises through 40 wells to be exported through a series of pipes at over 2,000 miles-per-hour. That's a lot of gas at a high speed from a structure that weighs 656,000 tons with new gas compressors scheduled to further increase production volume from Troll A.