The Petronas Twin Towers, and the record that rested on two spires
Kuala Lumpur took the world height record off Chicago in 1998 by ten meters, and the argument that followed made the measuring rule more famous than either building.
The numbers
The Petronas Twin Towers are 452 m (1483 ft) tall, have 88 floors each, and were completed in 1998 at Kuala Lumpur City Centre. Cesar Pelli, the Argentine-born American architect who also drew the World Financial Center in New York, won the design competition. The official opening came a year after completion, on 31 August 1999, Malaysia's independence day.
They were the tallest buildings in the world from 1998 until Taipei 101 passed them in 2004. They are still the tallest twin towers anywhere, and no pair of equal towers built since has come near them.
The record was in the spires
Kuala Lumpur beat Chicago by about ten meters, and every one of those meters is spire. The Willis Tower has 108 floors to the Petronas towers' 88, a higher roof, and far more occupied space above 400 m. What it does not have is a spire: its twin masts are broadcast antennas, bolted to the roof by a television company rather than drawn by the architect.
The Council on Vertical Urbanism counts a spire as architectural height and an antenna as equipment. By that rule Kuala Lumpur won, and Chicago spent years pointing out that a visitor on the top floor of the Willis Tower is higher than one on the top floor of either Petronas tower. Both sides were right, because they were measuring different things. The row taught a general audience how tall buildings are measured, and the separate categories it forced into the open are the onesthe record list still uses.
An eight-pointed star
Each tower's floor plan starts from two squares rotated against each other into an eight-pointed star, the Rub el Hizb motif of Islamic geometry. Pelli then cut into the figure: eight semicircles fill the notches between the points, because a star with sharp corners gives an office tenant unusable floor area.
Above the lower floors the plan steps inward in five tiers, each a smaller version of the same star. That is where the tapered profile comes from, and the setbacks shed wind load as the tower thins. The steel and glass skin repeats the pattern in horizontal bands.
The skybridge that is not attached
A double-decker bridge links the towers at floors 41 and 42, 58 m long and about 170 m above the ground. It carries tenants between the two buildings without a trip down to the plaza.
The bridge is not fixed to either tower. In wind each tower moves on its own, by different amounts and sometimes in different directions, and a rigid connection would be torn apart within a season. So the deck rests on spherical bearings and slides in and out of both buildings as they lean. Two legs angled up from the 29th floor carry its weight, meeting it in a V that is the most photographed piece of structure in Malaysia. The movement itself is ordinary:towers are built to sway.
Two towers, two contractors, one race
Petronas split the job. A Japanese consortium led by Hazama built Tower 1, a South Korean consortium led by Samsung built Tower 2, and the two crews worked side by side on identical designs, each able to see exactly how far along the other was.
Tower 2 started later and finished first. It also went up out of plumb: surveyors found it leaning by about 25 mm, enough to matter over 88 floors, and the upper structure had to be corrected back onto its axis. Both towers had to arrive at the same height, because the bridge between them was fabricated to one length.
No bedrock worth reaching
Kuala Lumpur sits on limestone riddled with caves and sinkholes, and at the chosen site the usable rock sloped away steeply. Test drilling found no bedrock at a depth anyone could build on. The towers were moved about 60 m across the plot, onto ground where the soft material was at least consistent, and the attempt to reach rock was given up.
They stand instead on 104 barrette piles, rectangular concrete shafts rather than round ones, sunk as deep as 114 m and carried by friction against the soil. They were the deepest building foundations in the world when they were poured, under a raft 4.5 m thick. Each tower weighs around 300,000 tons, becausethe frame is high-strength reinforced concrete, not steel. Malaysia had no steel industry of its own and imported steel was expensive, while concrete was cheap and local. It is also stiffer, which suited a tower holding one end of a 58 m bridge.
Going up
Tickets cover the skybridge and then the observation deck on floor 86, and the lift ride from the basement to the top takes about 90 seconds. The deck is the highest point open to the public; the floors above it hold offices and the spires are structure rather than space.
Entry is from the concourse of the Suria KLCC mall at the base, visitor numbers per time slot are capped, and slots sell out days ahead in holiday season. The towers are lit after dark, which is the view most people know from photographs. For company at this height, seethe supertall class.