Twin Towers

The Petronas Twin Towers (also known as the Petronas Towers or Twin Towers), in Kuala Lumpur, Malaysia were the world's tallest buildings, before being surpassed by the Taipei 101. However, the towers are still the tallest twin buildings in the world. Tower 2 was built by Samsung Engineering & Construction and Tower 1 by Hazama Corporation [1]. They were the world's tallest buildings from 1998 to 2004 if measured from the level of the main entrance to the structural top, the original height reference used by the US-based Council on Tall Buildings and Urban Habitat from 1969 (three additional height categories were introduced as the tower neared completion in 1996).
COMPARISION WITH OTHER STRUCTURES
The Petronas Twin Towers were the tallest buildings in the world until Taipei 101, as measured to the top of their structural components (spires, but not antennas), took over the record. Spires are considered integral parts of the architectural design of buildings, to which changes would substantially change the appearance and design of the building, whereas antennas may be added or removed without such consequences. The Petronas Twin Towers remain the tallest twin buildings in the world.

The Sears Tower and the World Trade Center towers were each constructed with 110 occupied floors – 22 more than the Petronas Twin Towers’ 88 floors. The Sears Tower and the World Trade Center’s roofs and highest occupied floors substantially exceeded the height of the roof and highest floors of the Petronas Twin Towers. The Sears Tower’s tallest antenna is about 250 feet (76 metres) taller than the Petronas Twin Towers’ spires. However, in accordance to CTBUH regulations and guidelines, [3] the antennas of the Sears Tower were not counted as part of its architectural features.[4]Therefore, the Petronas Twin Towers exceed the official height of the Sears Tower by 10m, but the Sears Tower has more floors with occupied office space at a higher level.
History
Designed by Argentine-American architect César Pelli, the Petronas Towers were completed in 1998 and became the tallest buildings in the world on the date of completion. The 88-floor towers are constructed largely of reinforced concrete, with a steel and glass façade designed to resemble motifs found in Islamic art, a reflection of Malaysia's Muslim religion. They were built on the site of Kuala Lumpur's race track. Because of the depth of the bedrock, the buildings were built on the world's deepest foundations. The 120-meter foundations were built by Bachy Soletanche, and required massive amounts of concrete.

In an unusual move, a different construction company was hired for each of the towers. According to both a National Geographic documentary and a Korean newspaper, Tower 2 was successfully completed by Samsung Constructions, Kukdong Engineering & Construction (both of South Korea). The builders of Tower 1, Hazama Corporation found a problem during the construction, the tower was estimated to lean 25mm on the ground with its own weight. While Hazama's work to fix the problem, Samsung Constructions completed their work. Finally, the Tower 2 construction team succeeded one month earlier than tower 2. [5] [6]. Due to a lack of steel and the huge cost of importing steel, the towers were constructed on a cheaper radical design of super high-strength reinforced concrete. High-strength concrete is a material familiar to Asian contractors and twice as effective as steel in sway reduction; however, it makes the building twice as heavy on its foundation than a comparable steel building. Supported by 23-by-23 meter concrete cores and an outer ring of widely-spaced super columns, the towers use a sophisticated structural system that accommodates its slender profile and provides from 1300 to 2000 square metres of column-free office space per floor.

Below the twin towers is Suria KLCC, a popular shopping mall, and Dewan Filharmonik Petronas, the home of the Malaysian Philharmonic Orchestra.

Petronas, Malaysia's national oil company, set out to build the world's tallest building. Although other buildings such as the Sears Tower have higher occupied floors, a higher antenna, and a higher roof, the Petronas Twin Towers' spires are classified as architectural details and rise to 452 m (1483 feet), giving it the greatest structural height until Taipei 101. Taking advantage of the rules governing building measurements (counting spires but not antennas) has generated controversy over the towers' claim to the title. However, the tradition of including the spire on top of a building and not including the antenna dates back to the rivalry between the Chrysler Building and the 40 Wall Street.
Other buildings have used spires to increase their height but have always been taller overall to the pinnacle when trying to claim the title. In the aftermath of the controversy, the rules governing official titles were partially overhauled, and a number of buildings re-classified structural antenna as architectural details to boost their height rating (even though nothing was actually done to the building).
SKYBRIDGE
The towers feature a skybridge (constructed by Kukdong Engineering & Construction) between the two towers on 41st and 42nd floors, which is the highest 2-story bridge in the world. The bridge is 170m above the ground and 58 m long, weighing 750 tons. The same floor is also known as the podium, since visitors desiring to go to higher levels have to change elevators here. The skybridge is open to all visitors, but free passes (limited to 1700 people per day) must be obtained on a first-come, first-served basis. The Skyway is closed on Mondays. Visitors are allowed to go only on the 41st floor as the 42nd floor can only be used only by the tenants of the building.

The skybridge also acts as a safety device, so that in the event of a fire or other emergency in one tower, tenants can evacuate by crossing the skybridgeto the other tower. However, the total evacuation triggered by a bomb hoax on September 12, 2001 (the day after the September 11 attacks destroyed the Twin Towers of the World Trade Center in New York City) showed that the bridge would not be useful if both towers need to be emptied simultaneously, and the capacity of the staircases was insufficient for such an event. Plans thus call for the lifts to be used if both towers need to be evacuated, and a successful drill following the revised plan was conducted in 2005.


The Lift System
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 odd numbered floors and upper deck to even numbered floors. In order to access an even numbered floor from ground level, passengers are required to use an escalator to access the upper deck of the elevator.
From the ground floor, there are three groups of lifts. The "short haul" group of 6 lifts take passengers to floors between level 2/3 and level 16/17. The "mid haul" group of 6 lifts take passengers to floors between level 18/19 and level 37/38. There is also a set of shuttle lifts that take passengers directly to levels 41/42. In order to get to levels above 41/42, passengers are required to take the shuttle lifts and then change lifts to the upper floors. These connecting lifts are placed directly above the lifts serving levels 2 to 38. The pattern now repeats with the upper levels, one set serving levels 43/44 to 57/58 and one set serving levels 59/60 to levels 73/74.

Apart from this main bank of lifts, there are a series of "connecting" lifts to take people between the groups. Unlike the main lifts, these are not the double-decker type. Two lifts are provided to take people from levels 37/38 to levels 41/42 (levels 39 and 40 are not accessible as office space). This avoids the need for someone situated at the lower half of the building to go down to the ground floor in order to gain access to the upper half of the building.

The lifts contain a number of safety features. It is possible to evacuate people from a lift stuck between floors by manually driving one of the adjacent lifts next to it and opening a panel in the wall. It is then possible for people in the stuck lift to walk between elevator cars.

During an evacuation of the buildings, only the shuttle lift is allowed to be used. This is because there are only doors at levels G/1 and levels 41/42 therefore should there be a fire in the lower half of the building, this enclosed shaft would remain unaffected.