PETRONAS TOWERS

INTRO

The Petronas Twin Towers are twin high rises located in Kuala Lumpur, Malaysia. They were designed by Argentinean-American architect Cesar Pelli and built by two separate construction consortiums headed by Hazama Corp. and Samsung Engineering and Construction between the years 1992 and 1997.

The Towers have 88 stories each and stand 1,483 feet (452 m) tall. The Council on Tall Buildings and Urban Habitat certified the Towers as the world’s tallest buildings in 1996, based on their structural top. They retained the title until 2004 when the Taipei 101 surpassed them.The project cost US$1.8 billion to build.

DESIGNING

The design for the PETRONAS Towers was not a written document or a set of drawings for the contractors to follow when building the structure.  It was instead an evolving process that took place over the course of many years.  This enormous amount of communication and the design considerations that were discussed produced a final result that differs considerably from the plan that won the first Kuala Lumpur City Center design competition held in 1991.

The high quality of the PETRONAS Towers is the result of the quality of the design team.  Although César Pelli was the titular designer and he served as the lead visionary, the design contributors included Prime Minister Dr. Mahathir, businessman T. Ananda Krishnan, senior managers of the PETRONAS company, the Kuala Lumpur City Center planning manager Arlida Ariff, and many high ranking national and local politicians.

CONSTRUCTION

Foundation

The Petronas Twin Towers were going to be constructed on a former horse race track in Kuala Lumpur called Selangor Turf Club. However, it was soon discovered no proper survey of the site was ever done. So the companies began drilling boreholes searching for bedrock to support the towers. “What we found was we were sitting not only on some decayed limestone, but we were sitting on the edge of a cliff,” said Pratt.
Essentially, one side of the site was limestone, but the rest was soft brittle rock that would crumble under the pressure of the tower. So, structural engineer Charlie Thornton suggested moving the whole site about 200 feet (61 m), putting it entirely upon the soft ground. They would then have to drive piles deep into the earth to stabilize a concrete raft situated underneath the giant towers.
Excavation began in January 1993 to create “an underground ‘forest’ of columns made of concrete and steel.” One hundred and four concrete piles, ranging from 200 to 375 feet (61 to 114 m) deep, were bored into the ground. Then the concrete raft was poured in one continuous 54-hour period (one truck load every 2.5 minutes).[8] The concrete was poured continuously to ensure it dried evenly, otherwise the whole slab could crack.

Plan evolution of Petronas Towers

Five hours into the pour, a heavy tropical storm hit the construction site forcing them to cover the concrete raft with canvas tarps while continuing to pour. The 54-hour pour was successful.It held the world record for most concrete pour at one time. The raft was 15 feet (4.6 m) thick and weighed 32,500 tons.

Super Structure

Designing the superstructure of the building presented another set of challenges. Although the tallest skyscrapers are steel structures, that material was not readily available in Malaysia, where prohibitively high tariffs on imported steel make concrete the construction material of choice.

Damper

Furthermore, steel buildings tend to be more flexible than concrete ones and sometimes have to be fitted with mechanical devices known as tuned mass dampers to ameliorate the effects of vibrations induced by the wind. Concrete structures, on the other hand, although they tend to be stiffer and have qualities that damp out quickly any vibrations that do begin, often are bulkier-looking than steel. Since the architect wished the Petronas Towers to be slender-looking and have columns spaced rather far apart, conventional concrete columns would have been too aesthetically broad and structurally heavy. To overcome this objection, an extremely high-strength concrete was developed, with bearing capacities as much as three times that of concrete conventionally used in Malaysia, or elsewhere for that matter.

Special concrete mixes, using local materials, were developed to produce compressive strengths as high as 10,000 pounds per square inch, with quality control provided by state-of-the-art computerized systems. Being made of high-strength concrete, the columns around the periphery of the towers could be smaller in diameter and lower in mass, thus reducing their dead weight. Still, at the base of the towers, the columns are nearly eight feet in diameter. The towers are not purely concrete structures, however, and the floor beams spanning between each building's core and ring of columns are made of steel. This was done to speed construction, minimize the floor height and better accommodate such mechanical equipment as cooling ducts. The tapering at the top of the building demanded some especially tricky structural engineering, and its geometry necessitated the installation of a wide variety of different-size glass panels. The record height of the towers is achieved through the pinnacles at their tops, which are part of the basic architecture and structure proper, unlike the broadcast antennas erected after the fact on such buildings as the Empire State Building and the Sears Tower.

The TWIN TOWERS

The towers will also be connected to each other at the level of the sky lobbies by a sky bridge, a 190 foot-long steel walkway that not only will facilitate movement between one tower and the other but also will serve as an alternative escape route in the event of a fire or other emergency, such as occurred when the terrorist bombing forced the evacuation of one of the towers of the World Trade Center. But the sky bridge's design presented additional and unusual structural problems. Since the two towers can sway in the wind both in phase and out of phase, as well as twist in independent directions, the sky bridge could not be attached rigidly between the vertical structures. Thus special bearing connections had to be devised to allow for as much as 12 inches of horizontal movement each way at each end, as well as the twisting. Because such a long, unsupported sky bridge would have to have been of very heavy construction if it were not to sag in the middle, a set of slender steel legs was designed to angle up from supports on each tower about 160 feet below to the center of the sky bridge. To prevent such slender struts from vibrating excessively in the wind, thus presenting the potential for uncontrollable motion or at least the accelerated growth of fatigue cracks, tuned mass dampers were designed to be installed inside the legs. (Each mastlike pinnacle also has a damper in the form of an energy-absorbing, rubber-sheathed chain.)

FEATURES

Lift

The main bank of Otis Lifts is located in the centre of each tower. All main lifts are double-decker with the lower deck of the lift taking passengers to even-numbered floors and upper deck to odd-numbered floors. To reach an odd-numbered floor from ground level, passengers must take an escalator to the upper deck of the lift.
There are 29 double-deck passenger elevators, but there are different sets that service certain floors of the towers, specifically two sets of six of these double-deck passenger elevators to floors 1–23 and 1–37 respectively. Another set of 5 passenger lifts transport passengers to the 41st and 42nd floors where they can switch lifts to reach the upper zones of the buildings, each double-deck passenger lift with the capacity of 52 passengers or, 26 passengers per deck. There are also 6 heavy-duty elevators for utility.

Sky Bridge

Sky bridge between the Towers

The towers feature a double Decker sky bridge connecting the two towers on the 41st and 42nd floors, which is the highest 2-story bridge in the world. It is not attached to the main structure, but is instead designed to slide in and out of the towers to prevent it from breaking,[30] as the towers sway several feet in towards and away from each other during high winds. It also provides some structural support to the towers in these occasions. The bridge is 170 m (558 ft) above the ground and 58.4 m (192 ft) long, weighing 750 tons.]The same floor is also known as the podium, since visitors going to higher levels have to change elevators here. The skybridge is open to all visitors, but tickets are limited to about 1000 people per day, and must be obtained on a first-come, first-served basis. Initially, the visit was free but in 2010, the tickets started being sold by Petronas. Visitors can choose to opt for package one which is just a visit to the skybridge or go for package two to go to the skybridge and all the way to level 86.[ Visitors are only allowed on the 41st floor as the 42nd floor can only be used by the tenants of the building.