The Fall of Skyscrapers - Pushing the Limits: New Adventures in Engineering - page 115

also be a way for fleeing people to breathe in such an environment. Such systems would need to
possess a robustness and redundancy to survive tremendous impact forces, and they might be unat-
tractively bulky and prohibitively expensive to install. Other approaches might include more effect-
ive fireproofing, such as employing ceramic-based materials, if they could be made shatterproof,
thus at least giving the occupants of a burning building more time to evacuate.
The evacuation of tall buildings is now given much more attention by architects and engineers
alike. Each World Trade Center tower had multiple stairways, but all were in the single central
core of the building. In contrast, stairways in Germany, for example, are required to be in different
corners of the building. In that configuration, it is much more likely that at least one stairway will
remain open if, for example, an airplane crashes into another corner. But locating stairwells in the
corners of a building means, of course, that prime office space cannot be located there. In other
words, most measures to make buildings safer also make them more expensive to build and dimin-
ish the appeal of their space. This dilemma is at the heart of the reason why the future of the super-
tall building is threatened.
It was unlikely that, in the immediate wake of the World Trade Center collapses, any supertall
building then in the development stage, in the United States at least, would not have been put on
hold and reconsidered. Real-estate investors want to know how a proposed building will stand up
to the crash of a fully fueled jumbo jet, how hot the ensuing fire will burn, how long it will take to
be extinguished, and how long the building will stand so that the occupants can evacuate. They also
raise the question of who will rent the space if it is built.
Potential tenants naturally have the same questions about terrorist attacks. Companies wonder if
their employees will be willing to work on the upper stories of a tall building. Managers wonder if
those employees who do agree to work in the building will be constantly distracted, watching out
the window for approaching airplanes. Corporations wonder if clients will be reluctant to come to
a place of business perceived to be vulnerable to attack. The very need to have workers grouped
together on adjacent floors in tall buildings is called into question.
After the events of September 11, the incentive to build a signature structure, a distinctive su-
pertall building that sticks out in the skyline, was greatly diminished. In the wake of the tragedy,
as leases came up for renewal in existing skyscrapers, real-estate investors watched closely the
downward movement in occupancy rates. It may be that some of our most familiar skylines may
be greatly changed in the foreseeable future. Indeed, if companies move their operations wholesale
out of the most distinctive and iconic of supertall buildings and into more nondescript structures of
moderate height, it is not unimaginable that cities such as New York and Chicago will in time see
the reversal of a long-standing trend. We might expect no longer to see developers buying up land,
demolishing the low-rise buildings on it, and putting up a taller skyscraper than those in the vicinity.
Instead, owners might be more likely to disassemble the top of or entirely demolish a vacant sky-
scraper and erect in its place a building that is not significantly smaller or taller than its neighbors.
Skylines that were once immediately recognizable—even in silhouette—for their peaks and valleys
may someday be as flat as a mesa.
There is no imperative to such an interplay between technology and society. What happens ulti-
mately will depend largely on how governments, businesses, and individuals react to terrorism and