"Building on Ground Zero" features candid interviews with leading construction and safety experts, investigators, architects, and engineers—including Leslie Robertson, lead structural engineer of the original World Trade Center and Shanghai's new World Financial Center, and Jake Pauls, occupants advocate and evacuation specialist. From the hallways of the newly erected World Trade Center 7 in New York, to China, where the world's tallest building is midway to completion, NOVA explores the complex challenges of building tall buildings in the wake of 9/11.
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Previously, it was natural threats to the safety of tall buildings—earthquakes, hurricanes, and the relentless force of the wind—that had driven structural engineering codes. But with the threat of terrorism, determined attackers have targeted even the most secure structures, forcing engineers and architects to consider what was once unimaginable.
In the months after 9/11, NOVA followed a team of engineers tasked by FEMA to study the Twin Towers' collapse. Preliminary conclusions originally reported in "Why the Towers Fell" determined that the floors of the buildings may have "pancaked" down upon one another as their trusses failed. Now, with the benefit of years of additional investigation, the National Institute of Standards and Technology (NIST) has revealed that no structural element was to blame for the buildings' collapse.
Using vivid computer animations, NOVA takes viewers through a simulation of what the buildings endured in the 9/11 attacks. It turns out that fireproofing on the floor trusses was blown off by the impact of the jets, exposing the trusses to severe fire temperature. This caused the trusses to bow and eventually break the buildings' supporting columns, which then triggered the immediate collapse of the buildings. (See an audio slide show narrated by the chief NIST investigator.)
Forensic engineer Eugene Corley also details the chilling results of another critical engineering investigation, that of the bombing and destruction of the Alfred P. Murrah Federal Building in Oklahoma City. Unlike the World Trade Center towers, which stood for 56 minutes (South Tower) and one hour 42 minutes (North Tower), the Murrah Building crumbled in a mere three seconds. In this worst-case scenario, known as a progressive collapse, there was simply no time for anyone to escape.
By standing as long as they did, the Twin Towers gave most people a chance to escape. (Hear one survivor's remarkable tale of escape from high in the South Tower.) So structurally they were very sound. But their ultimate collapse revealed fatal weaknesses that many tall buildings share. These include stairways that are too few and too narrow to accommodate crowds of evacuees, fireproofing materials that are easily dislodged and could leave steel exposed to dangerous levels of heat, and insufficient means by which firemen and other First Responders can reach the upper floors of a building in an emergency.
These issues and more have been addressed by NIST in a comprehensive report that recommends 30 safety revisions to American building codes. But as NOVA learns, these recommendations are not without controversy among builders or even among those in the emergency planning community. Code changes often come with significant added costs, swift evacuations of giant structures may not be possible, and the probability of future terrorism is difficult to quantify. Most experts concede that protecting buildings from airplane attacks like those that took down the Twin Towers is simply not practical. But many improvements can be made to a building's design, structural integrity, and evacuation systems that would better protect it from major fire or even some terrorist threats, and NOVA details the ways this can be done.
"Building on Ground Zero" takes viewers to two structures that exemplify bold advances in skyscraper safety and construction. In New York City, World Trade Center 7 has risen from the ashes as one of America's safest and "greenest" tall buildings. And in China, NOVA gets a tour from Leslie Robertson as he guides the construction of Shanghai's new World Financial Center, which upon completion will be the tallest building in the world. (Hear Robertson describe its unique design and safety features.)
Exclusive footage shows off the skyscraper's massive structural shell, "refuge floors" with extra fire protection, and additional elevators designed for use by emergency personnel. While Robertson is relieved that the NIST investigation found no flaw in his engineering of the World Trade Center, the horror of what happened to the Towers still haunts him to this day. In Shanghai, he is doing what many argue we all must do: take the lessons from Ground Zero, endorse innovation, and continue to reach for the sky.