Top 5 Megastructures In The World

Since the reign of the pharaohs, the lure of the very large has proven irresistible to visionary architects and game-changing engineers. Ancient Egypt had its pyramids, the Chinese dynasties had their Great Wall and modern Dubai has its. well, pretty much everything.

At the heart of every megastructure is a dare: how far can you go? And every few years or so, some ambitious billionaire ups the ante, going higher, longer, deeper and more wildly expensive.

The 828-metre (2,717-foot) Burj Khalifa tower in Dubai makes your palms sweat just looking at pictures from the observation deck. And not to be outdone, Dubai’s Palm Islands are visible from space with the naked eye.

None of these mind-blowing projects would be possible without quantum leaps in structural engineering, materials science, construction technology and logistics. In these post, we’ll explain the extreme engineering behind extraordinary structures.

The Millau Viaduct

The Millau ViaductMajestic and minimalist, the world’s longest bridge is also one of the most beautiful.

From a distance, the seven steel masts of the record-breaking Millau Viaduct in southern France look like billowing sails of a cosmic spacecraft.

Up close, the tallest bridge in the world is no less stunning, a minimalist masterpiece that resembles an Apple iPad in bridge form.

The Millau Viaduct is a cable-stayed road bridge of concrete and steel with load-bearing masts stretching 343 metres (1,125 feet) into the air. 17 years in the making – at a cost of 400 million euros – the 2,460-metre (1.52-mile) span employed the very latest construction techniques and technologies during each of its six stages of fabrication and assembly.

First came the ‘legs’ of the bridge, seven thick piers consisting of 206,000 tons of poured concrete. The smooth, seamless surface of each pier was achieved using a machine called a self-climbing framework. Powered by hydraulic lifters, the concrete framework rises upwards with the pier at a rate of three meters every three days. Pouring continuously, the piers rose from the valley floor, reaching their peak heights in ten months.

Next came the deck, built from 173 steel box beams forged in the Eiffel factory. Using two on-site metalworks, the steel floor was welded to the box beams to create 171-metre deck panels. The panels were then ‘launched’ from both sides of the bridge using 64 hydraulic conveyors positioned atop the piers and temporary steel crutches. The two sides of the deck literally slid towards each other at a rate of 60cm per push, equal to nine metres an hour. The two sides finally met on 28 May 2004 at 2:12pm.

The seven steel masts support 1,500 tons of steel stays attached at 11 paired points. Each stay consists of up to 91 bound steel cables and each cable is made from seven individual strands of steel. The stays are triply weatherproofed to avoid corrosion.

Before paving the road, workers used high-pressure blasters to scour the steel deck with millimeter-size ball bearings. Once all traces of rust were removed, special equipment laid a four-centimeter thick layer of tar thermosealed at 400”C, offering complete corrosion protection.

The bridge construction is guaranteed for 120 years and is continuously monitored for movements as small as a micrometre by dozens of fibre-optic sensors strung throughout the structure.

Extreme islands

Extreme islandsSheikh Mohammed bin Rashid Al Maktoum has only one requirement for construction projects in his desert nation of Dubai: if it doesn’t break a world record for tallest, biggest or most expensive, he’s not interested. It shouldn’t surprise, therefore, that the original design of the Palm islands -three man-made islands of colossal proportions off the coast of Dubai – came from the Sheikh’s own pen.

But how do you build the world’s largest man-made islands? Luckily, Dubai has almost as much sand as it does oil money. The state-run developer Nakheel hired the Dutch dredging firm Van Oord, specialists in land reclamation, to suction up millions of cubic metres of sand from the sea floor and precision spray it into the shape of a huge date tree with 16 slender fronds extending into the sea. Van Oord’s dredging equipment is guided by DGPS (differential global positioning system), NASA’s new real-time positioning technology that’s accurate down to ten centimeters.

The first stage of each of Dubai’s artificial island projects – the three Palm islands, plus a 300-island cluster in the shape of the continents called The World – is to install an artificial barrier reef as a water break. The artificial wall for The World, consisting of 34 million tons of carefully stacked rocks, is 27km long. The dredging team then builds each island or peninsula in stages, using heavier machinery for the island foundations and ‘rainbowing’ sand sprayers to finish the above-water detail work.

To prevent erosion, the base of the islands is reinforced with a layer of geotextile fabric that absorbs the impact of waves. The huge piles of loose sand are also treated to vibrocompaction, a process that uses water saturation and high-intensity vibrations to ‘densify’ the soil structure.

When complete, the Palm islands and The World will upgrade Dubai’s beachfront property from a 37-mile stretch of condo-clogged real estate to 600 miles of pristine sand. In case you’re wondering, a starter home on the smallest island starts at GBP 1.3 million (USD 1.9 million).

Laerdal Tunnel

Laerdal TunnelAn ambitious dig gives drivers an unprecedented journey through the centre of the Earth.

A decade ago, the drive from Oslo to Bergen, Norway required travellers to ferry multiple fjords and summit 1,600-metre peaks subject to rockslides and piles of snow. In 2000, King Harald V cut the ribbon on the Laerdal Tunnel, a 24.5km (15.2-mile) passage beneath the mountain ranges and waterways that had made travel between the two coastal cities so daunting and slow. Laerdal is by far the longest road tunnel in the world, beating the previous record-holder by seven kilometres.

Over five years, workers excavated 2.5 million cubic metres of rock. The tools of the trade were explosives and satellite-guided drilling jumbos.

The blasting crew executed over 5,000 precision explosions each requiring 100 individually drilled holes, 5.2 metres deep, filled with an explosive called Anolit. Drilling rigs were guided by satellite positioning and on-board laser beams. Without this technology, it would have been impossible for the two excavation teams to meet each other over 10km inside the heart of the mountains.

To break up the monotony of the 20-minute subterranean drive, engineers divided the tunnel into four distinct sections separated by three wide, blue-lit caverns that give the sensation of an artificial sunrise.

Taipei 101

Taipei 101Building a skyscraper in Taipei is like playing Jenga on a trampoline. The Taiwanese capital, located along the famed Ring of Fire, sits atop an active seismological zone with a very long history of deadly earthquakes. As recently as 1999, a 7.3 trembler killed over 2,400 people. As if the earthquakes aren’t enough, Taipei is also directly in the path of 26 annual tropical storms and typhoons, the Pacific equivalent of hurricanes.

Why would anyone attempt to build the world’s tallest building on such shaky (and blustery) ground? You obviously don’t know many engineers. The challenge of building a 508-metre megastructure in such an inhospitable location calls for elegant and ingenious solutions, two words that accurately describe Taipei 101, the 101-storey superscraper that was – until the completion of the Burj Khalifa in Dubai – the tallest man-made structure in the world.

Taipei 101 was designed to resemble a bamboo shoot, rising upwards in eight sections (a lucky number in Chinese) with walls angled outward at seven degrees. Like a slender stalk of bamboo, the record-breaking tower was designed to be both strong and flexible – bendable, but unbreakable.

Taipei 101’s strength begins in its roots, 380 concrete piles driven 80 metres through the island’s thick clay sediment to reach solid bedrock. The building is widest at its foundation, narrowing at a five-degree angle for 25 floors before arriving at the first of the eight identical sloped sections. The tower’s core stability comes from eight forged steel megacolumns, each measuring 3.001×2.401 and filled with concrete. The megacolumns are trussed to the building’s outward-sloping frame with ductile steel braces that bend in an earthquake.

At 700,000 tons of steel, concrete and glass, Taipei 101 is actually light for its height. To steady the tower in gale-force winds, it’s equipped with an internal pendulum called a “passive tuned mass damper’, whose massive weight (660 tons) pulls instinctively in the opposite direction of swaying. The result is not only one of the tallest, but perhaps the most stable building in the world, designed to withstand a 2,500-year seismic shock.

The Damper

The DamperSuspended from the centre of the 92nd floor of the world’s second tallest building is a 660-ton, GBP 543,000 (USD 800,000) steel ball hanging from four sets of steel cables. The function of the tuned mass damper isn’t to keep Taipei 101 upright (its concrete-filled steel backbone is more than sufficient to do this), but to cancel out nausea-inducing swaying in a powerful storm.

If wind pushes the tower to the right, the dangling damper will provide an immediate and equal force to the left, cancelling out the motion. Like a shock absorber in a car, the damper is attached to a series of hydraulic pistons that convert dynamic energy – the swaying of the ball – into heat. Not only is the Taipei 101’s damper the largest of its kind, but it’s the only one in the world to be incorporated into the aesthetic design of the structure, easily visible from observation decks and restaurants.

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