The functional structures of the PETRONAS Towers were designed by the structural engineers Thornton-Tomasetti, with headquarters in New York, and Ranill-Berskutu of Malaysia. The core structure of each of the towers is composed of a ring of sixteen cylindrical columns of high strength reinforced concrete. The columns vary in size from 2.4 meters in diameter at the lower areas to 1.2 meters in diameter at the top, and are placed at the outside corners and additional arcs of the eight pointed star shape that gives the buildings their classic Islamic shape. In a staging of six increments, the columns slope slightly inward as they rise, resulting in the tapered form of the final buildings. The columns are linked with a series of concrete core walls and ring beams and the architect César Pelli has described these movement-resistant and damper-free structures as a pair of “soft tubes”. There are actually two concentric pressurized cores in the structures, and the two cores unite at the 38th floor of each tower.
A significant choice of building materials was made early in the project, and it was decided to use reinforced concrete instead of the structural steel that is more common in other skyscrapers. This choice was made not only because local Malaysian contractors were more experienced building with concrete than with steel, but also because the cost of importing all the steel would have been prohibitive, whereas the concrete could be obtained locally. The final towers weigh more than twice what they would have had steel been used, but it was additionally felt that the use of concrete would more effectively dampen sway in windy conditions and reduce vibrations within the towers.
The structural plan liberates additional floor space inside the towers by locating the mechanical services for the towers in two “bustles” that are 43 story tall buildings located immediately adjacent to the towers. After completion, the exteriors of the two concrete “soft tubes” were clad in stainless steel and glass with a design that originated in the classic geometric patterns of ancient Islamic art. The foundations for the structures are huge concrete cores and are considered the deepest building foundations in the world.
The two 73-meter tall pinnacle structures of the towers were, like the towers, constructed by two different contractors. One of the pinnacles was fabricated in Japan and the other in Korea. Built of structural steel and then disassembled and shipped to Kuala Lumpur, the pinnacles were reassembled and mounted atop the towers in yet another delicate operation that required several months of practice before the final installation. The two pinnacles are clad in brushed stainless steel.
Each tower used 11,000 tons of reinforcement steel, 2,825,120 cubic feet of high-strength concrete, almost 7,500 tons of structural steel beams and 830,000 square feet of glass windows.