After the World Trade Center’s twin towers fell, some urban analysts predicted the death of the skyscraper. But construction trends in the five years following 9/11 have proved otherwise. While reaching new heights with their structures, architects are also paying unprecedented attention to incorporating safety and security into their blueprints.
BUILDING UP ACROSS THE WORLD
A look at tall-building construction worldwide indicates the strength of the skyscraper’s popularity. More than a quarter of the world’s 100 tallest buildings have been started or completed since 9/11. Among them is the Burj Dubai in Dubai, which when finished is expected to be the world’s tallest building at about 2,300 feet–twice the height of Chicago’s John Hancock Center.
TALL BUILDINGS SINCE JANUARY 2001
Buildings at least 400 feet or 30 stories tall completed, under construction, approved or proposed (by country)
None
1-10
11-50
51-100
More than 100
Cities with more than 50
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Toronto: 92
Chicago: 98
Las Vegas: 50
New York: 112
Miami: 103
Panama City: 113
So Paulo: 68
Moscow: 51
Tel Aviv: 54
Dubai: 339
Tokyo: 140
Shanghai: 124
Seoul: 112
Busan, S. Korea: 51
Guangzhou, China: 58
Bangkok: 118
Hong Kong: 593
Shenzhen, China: 124
Kuala Lumpur: 59
Singapore: 86
Jakarta: 77
IN AMERICA
Before Sept. 11, 2001, U.S. skyscraper production had been on a gradual uptick. But instead of weakening after the terrorist attacks on Washington and New York, construction experienced only a slight lull before taking off in 2004 and 2005.
U.S. SKYSCRAPER CONSTRUCTION
Tall buildings (30 stories or more) by year of start date, based on an average construction period of two years
1995: 11
1996: 18
1997: 18
1998: 21
1999: 39
2000: 32
2001: 36
2002: 36
2003: 33
2004: 59
2005: 101
AT GROUND ZERO
The World Trade Center site is being rebuilt with a series of skyscrapers exhibiting state-of-the-art security and safety features. The site will also include a transportation hub, a memorial and an arts center.
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The Freedom Tower:
One security-borne trend in skyscraper design is placing the building on a tall structure of highly fortified material. The Freedom Tower will rest upon a 186-foot-tall base of luminescent, blast-resistant glass. Designers planned the West Plaza (right) to complement the glass base with illuminated steps that flow down like a skirt.
HEIGHTS
Ground to top of antenna: 1,776 feet
Ground to top of building: 1,368 feet
Ground to top of base: 186 feet
7 WTC: A model for post-9/11 security
The first new building on the WTC site incorporates numerous security measures:
Fire protection: Fireproofing material is twice as thick and 10 times as adhesive as required by city code. The sprinkler system’s water-storage capacity is twice the amount required by city code.
Protective walls: Two-foot-thick concrete walls surround the building’s core, which encases the elevators and stairwells.
Exit stairs:
– Two stairways extend from the top floor to the fourth floor, where evacuees can exit through one of four emergency stairways directly to the outside.
– Stairway width is 66 inches, 20 percent wider than city code requires.
– Stairs are coated with glow-in-the-dark paint.
– Each stairway is pressurized to prevent smoke from entering.
– Blast-resistant cable-net wall: Thick, laminated glass provides a protective shield outside the lobby.
– Exterior metal screen: Provides an 80-foot tall zone around the concrete base that houses an electrical substation.
– High tenant floors: The first tenant floor is 110 feet above the street, limiting ground-based threats.
A stronger skin to celebrate light
For business and government buildings, skyscraper designers are increasingly adding more windows, reflecting the desire for more natural light as well as the metaphor for transparency. With safety in mind, builders are choosing glass made to shatter with minimal potential for injury.
TYPES OF GLASS USED IN SKYSCRAPERS
Annealed: Smoother, flatter, breaks into large shards.
Heat-treated: Has undergone heat treatment to become more resilient. Breaks into small pieces, instead of shards.
Tempered: Has undergone heat treatment and pressurization to become extremely strong, but is relatively distort-ed and not as smooth. Breaks into small pieces.
Laminated: Two panes of glass fused together. Cracks but does not break up.
Sources: Emporis, Skidmore, Owings & Merrill, Permasteelisa
– See microfilm for complete graphic.