Written for “Safe Buildings for This Century”
Australian Institute of Building Surveyors
National Conference, 12 – 13 August 2002
Darling Harbour, Sydney, Australia
THE WORLD TRADE CENTER AND 9/11:
A DISCUSSION ON SOME ENGINEERING DESIGN ISSUES
Lecturer, Department of Civil Engineering, The University of Sydney, NSW, 2006, Australia
This paper discusses the collapse of the World Trade Center towers in New York, on September 11,
2001, may affect structural design philosophies. There is a brief description of the WTC structural
system, followed by a short explanation of how the towers collapsed. Survivor accounts are given to
consider how the impact and fire affected emergency egress from the structures. The conclusions
from the initial report from the US Federal Emergency Management Authority (FEMA) are outlined.
Some recent changes to structural design standards are considered. The paper concludes by briefly
describing the redevelopment plans being considered by the Lower Manhattan Development
World Trade Center, WTC, 9/11, aircraft impact, fire engineering, collapse, structural robustness,
structural design, building standards, structural steel.
THE WORLD TRADE CENTER
Manhattan Island was much smaller in 1664 when the English took over a Dutch fort in New
Amsterdam, and the city of New York was born. Since European settlement, not only has the
population grown, but Manhattan has physically changed, as parts of both the Hudson and East Rivers
have been reclaimed. Figure 1 shows how the coastline of lower Manhattan has expanded since 1730.
The WTC site was once part of the Hudson River.
The architect for the WTC was Minoru Yamasaki, with the structural engineering led by John Skilling
and Leslie Robertson of Worthington, Skilling, Helle and Jackson. The ground breaking ceremony
was August 5, 1966, with the official ribbon cutting on April 4, 1973.
The two tower 100 s