How High Will They Build?

Atrium size is restricted. Water tanks on the roofs of tall buildings are sometimes engineered to let the water slosh about, doing double duty as wind dampers. Dedicated firemen's lifts are required in many Asian cities. "In Hong Kong they are required to reach any floor in the building in an extremely short period of time, so they are profiled like a bullet to avoid drag, and travel as fast as 9 meters per second," says Howeler.



"All this," he adds, "existed before 9/11. After 9/11, a lot of studies were carried out to determine if changes were necessary." Few were identified, but engineering responses to fire evolve. KPF decided to add a fifth stairwell to its planned Union Square because of evacuation concerns raised by harrowing stories from the WTC on September 11. At first the firm considered simply widening the stairwells, but realized that "a wider stair helps only if it is significantly wider, say, wider by an increment of a whole shoulder's width." Better five narrow stairwells than four that have been widened insufficiently for a crush.



Since September 11, Cesar Pelli has been constantly queried about the safety of the Petronas Towers and is outspoken in his belief that the concrete structures could withstand the impact of a jumbo jet. He points to the elevated bridge that connects the two buildings as an additional advantage: "That bridge could allow people to get from one tower to another in the case of such a catastrophe."
Howeler agrees that Asian tower construction is safer than that of the 30-year-old WTC, but warns that terrorism by its nature is hard to plan for. "The forms that terrorism takes seem to evolve and mutate faster than the architectural means to guard against them."



THE IDEA OF SUPERTALL TOWERS, vastly higher than anything now built, has long fascinated architects and urban planners. In 1956, Frank Lloyd Wright -- who had decried skyscrapers in the '30s and predicted the flight of people away from vertical cities -- designed the Illinois Tower, a mile high, 528 stories in all, to be occupied by 100,000 people.