How the Pentagon's Design Saved Lives on September 11Breaking News
tags: terrorism, 9/11
At 9:47 a.m. on September 11, 2001, a 62-year-old Pentagon employee and retired Air Force communications specialist was sitting in traffic west of the Pentagon when a roaring jet engine passed so low overhead that it clipped the radio antenna of the car behind him.
The airplane, the hijacked American Airlines Flight 77, sliced through three light poles in the Pentagon parking lot before slamming into the first floor of the building and exploding in a fireball, instantly killing 125 people inside the Pentagon plus all 64 passengers onboard, including the five hijackers.
While the act was horrific and all the losses on that day were devastating, structural damage analysis revealed that the death toll at the Pentagon could have been far worse, if not for some critical engineering decisions made 60 years earlier.
Construction of the Pentagon began, ironically enough, on September 11, 1941. While America had not yet entered World War II, President Franklin D. Roosevelt knew he needed a home base for impending military operations near the nation’s capital. Wartime urgency meant that the Pentagon was completed in record time—just 16 months using 15,000 construction workers.
Steel was rationed for the war effort, so the Pentagon was built almost entirely of reinforced concrete, including 41,000 concrete pilings and concrete ramps instead of stairs connecting the building’s five floors. Completed in 1943, the Pentagon remains the world’s largest low-rise office building with 6.5 million square feet of office space containing up to 26,000 workers.
When the Pentagon was built, no one knew that it would become an iconic monument to U.S. military power—or a target. In fact, the architects thought it would be abandoned after the war and turned into a massive record storage depot. Their prediction was wrong, but fortuitous.
Thinking the Pentagon would need to store heavy caches of records for the long haul, the U.S. Army Corps of Engineers built in excess strength and structural redundancies that would end up saving hundreds and potentially thousands of lives on 9/11.
Donald Dusenberry is a structural engineer who co-authored a landmark report for the American Society of Civil Engineers on the damage sustained by the Pentagon on 9/11 and the lessons learned from its resilience. Dusenberry was at Ground Zero in New York City just days after the Twin Towers fell and toured the Pentagon crash site a few weeks later.
What he and his colleagues discovered after carefully documenting and analyzing the damage inflicted on the Pentagon, was that even though 26 first-floor cement columns were completely destroyed and 15 others severely damaged by the fiery crash, the upper floors of the Pentagon didn’t immediately collapse. In fact, it was a full 30 minutes before a portion of the building directly above the crash site collapsed, allowing more than enough time for survivors to escape.
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