The Sept. 11 bombings killed almost 3,000 Americans. But if you exclude that unique event for the last two decades of terrorist activity, a different picture of US vulnerability appears.
Scarred by disastrous wars and thousands of deaths caused by terrorism, the world is still reeling from the events of September 2001.
Tragedies involving building collapses prompt structural engineers to figure out what happened, and how to prevent it from recurring.
Those involved with the monumental task faced many challenges as they balanced the unquestionable priority of remembrance with the commercial task of recreating an economically vibrant downtown.
Getting out in a crisis is often harder than it looks. But science can help.