SUPERTALL SCRUTINY

In presenting the changes that have occurred in the design of skyscrapers since September 11, 2001, in “Castles in the Air,” Mark Lamster notes three threats: aircraft impact, earthquakes and wind. He correctly claims that structural engineers are now able to effectively design against them.

Unfortunately, the Twin Towers collapsed primarily because of fire, and nowhere in the article is fire explicitly mentioned as a structural threat. On 9/11 we clearly saw that fire can cause entire modern high-rise buildings to collapse. (Indeed, 7 World Trade Center, a steel-framed high-rise, was not struck by an aircraft but collapsed because of fire ignited by debris from the Twin Towers.) To ensure safety in ever taller buildings, the potential impacts of uncontrolled fire need to be explicitly considered during the structural design process with the same care as earthquakes and wind. While changes in escape-stair width, firefighter communications systems and the addition of sky bridges (all noted by Lamster) can only improve life safety in tall buildings, they do not prevent structural collapse resulting from fire.

Preventing another 9/11 requires that the structural engineering and architecture communities own up to the reality of what uncontrolled fire can do to tall buildings and take the necessary actions.
Luke Bisby
Senior Research Fellow in Structures and Fire
University of Edinburgh

via scientificamerican.com