Building Petronas Towers
One of the first challenges of construction was anchoring the towers to the ground. The bedrock beneath the site was feared to be very irregular and Thornton-Tomasetti, the structural engineers, suggested relocating the towers about 200 feet (60 meters) so that they could bear on soil.
For the new location, they designed an underground forest of friction piles to provide provide greater distribution of the towers' weight. Over the piles was poured a reinforced concrete foundation mat, upon which the towers rest.
The towers are framed with a structure of concrete core walls and columns which, according to the engineers, was the best choice for several reasons. In Malaysia, the local contractors on the job were more familiar and comfortable working with concrete than with steel. Concrete also provided better stability to dampen the sway of the towers in winds, and minimized vibration.
Construction of the towers was fast paced, thanks in part to the decision to let two contracts, one for each tower, to two separate contractors. This naturally created a competitive environment, to the benefit of the building.
Building the Skybridge
One of the most dramatic feats was the placement of the two-story skybridge, which was built on the ground and hoisted to its location joining the 41st and 42nd floors. After it was lifted into position, the legs which had been installed on the towers were swung down into place, and connected under the bridge.
The skybridge was not a requirement of the building program, but as the project developed it became an essential part of the overall functions of the towers. It links two sky lobby levels in both towers permitting easy access to meeting rooms, an executive dining room and a Surau (prayer room), distributed between the towers.
Most interestingly, we discovered that by making the skybridge fire-rated and smoke-controlled, its mid-height location permits exiting from one tower to the other, as an alternative exit path. This reduces the cumulative demand in each tower and enabled us to avoid adding two fire stairs that would otherwise have been required from the sky lobbies down.
The structural design for the bridge was difficult because it had to accommodate possible differential movements of both buildings. The final solution was the simplest, clearest, and most elegant. It is an inverted V-shaped three-pinned arch that supports the bridge in the center, accommodating all movements while maintaining it equidistant from both towers.
One of the towers' most significant architectural characteristics is Eastern in nature: the space between them. The Petronas Towers are placed on a central axis, framing a doorway to the infinite with the skybridge.
In the spirit of Lao Tse, the Chinese philosopher who stressed that architecture's power lies not in its physical walls but instead in the space created by those walls, the towers together create a powerful super-scaled portal.
Cesar Pelli is principal of Cesar Pelli & Associates. Michael J. Crosbie is editor-in-chief of Faith & Form, a senior associate with Steven Winter Associates, and a contributing editor to ArchitectureWeek.
This article is excerpted from Petronas Towers: The Architecture of High Construction, copyright © 2001, available from John Wiley & Sons and at Amazon.com.
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