Pentagon Battered but Firm
So resilient was the newly strengthened section of the Pentagon that a glass display case only 40 feet (12 meters) from where the plane entered the building survived without a crack.
Countless additional injuries were
prevented because new windows in the renovated section were
"blast-resistant" and did not explode into flying glass splinters,
because new fire sprinklers operated as designed, and because alert
personnel turned off power and utilities to the affected areas before
Fortress of the Forties
The Pentagon was built during World War
II, in an amazing 16 months, to accommodate a consolidation of diverse
branches of the U.S. military establishment. The five-story building of
6 million square feet (560,000 million square meters) is actually five
concentric building rings separated by open-air courtyards, and
connected by ten radial corridors.
From inside to outside, the five rings of
buildings are labeled A through E. The airliner entered the ground
floor of the west face of the E ring and penetrated through the C ring.
Where the airplane struck, the impact, explosion, and fire brought down
all five stories and created a hole about 100 feet (30 meters) wide. In
the surrounding area, the newly stiffened walls remained only partly
damaged or not at all.
The primary structure of the Pentagon is
42,420 steel-reinforced concrete columns. Of these, only 32 were
destroyed and 15 seriously damaged. As recovery efforts continue, the
structure is being shored up with pressure-treated wood posts to
protect against further collapses.
Thus, in relative safety, workers have
been able to recover the remains of victims and to examine and clear
away debris. Within a week the airplane's voice and data recorders had
Ironically, the fortress-like appearance
provided by the exterior Indiana limestone is misleading. The limestone
is not structural but a veneer supported by steel hangers. As the
facade is repaired in the near future, matching replacement stone will
come from the original quarry in deference to the building's historic
The building was originally constructed as
five chevron-shaped wedges, and the fact that each of these has its own
independent mechanical and electrical systems further contributed to
minimizing the damage on September 11.
The Renovation Plan
The renovation plan, which began in 1993
with the construction of a power plant, was inspired in part by other
terrorist attacks in Oklahoma City and abroad. It was also made
necessary because the facility was woefully dysfunctional with leaking
pipes, a 60-year-old HVAC system including 17.5 miles (28 kilometers)
of ducts made from asbestos, a basement floor that had settled up to 12
inches (30 centimeters) in some areas, and electrical and
communications systems that had been incrementally jury-rigged to bring
them up from 1940s standards.
With Wedge One work nearly complete, a new
design/build team of architects, engineers, and builders had just begun
work on renovating Wedge Two. The total project was scheduled to
conclude in 2012. Although the repairs from the recent attack will
probably cost several hundred million dollars above the original
renovation budget, Pentagon officials expect the original renovation
schedule to be met.
In addition to major overhauls of the
mechanical and electrical systems, the Wedge One renovation included
the fire sprinklers, automatic fire doors, and the steel which saved
many lives on the day of the attack.
The blast-resistant windows were nearly
two inches (5 centimeters) thick. Some of them remain remarkably intact
and in place adjacent the point of impact. Some were popped out of
their frames by the force of the exploding jet fuel, but they fell
without breaking or splintering.
Also on the exterior walls, between the
steel columns, the renovation crew had placed Kevlar cloth, similar to
the material used for bullet-proof vests. This had the effect of
holding together building materials so they wouldn't become deadly
projectiles in an explosion.
As in the original building, the renovated
Wedge One kept independent mechanical and electrical systems which were
shut down shortly after the attack without affecting ongoing operations
of two-thirds of the building.
Already repair and clean-up work has
begun. Aside from the structural collapse, there was considerable soot
damage from fire, especially on the upper floors.
There are varying degrees of water damage
in about one third of the building. Some mold-infected carpets have
been quarantined until they can be cleaned or removed, and water has
destroyed valuable computers and documents.
So far, air quality levels have been
judged acceptable so as not to endanger clean-up workers. The new air
control system pressurizes air and forces the contaminates to remain in
the area of damage.
Learning from the Disaster
While Pentagon work continues, architects
and engineers are doing what they can to improve the security of their
projects elsewhere. Indeed, for DoD projects, any new construction or
major modifications is required to mitigate threats of both natural
hazards and attacks by explosives or chemical or biological weapons.
The Society of American Military Engineers
(SAME) will be holding a previously planned conference November 1-2, at
The Citadel in Charleston, South Carolina to educate professionals
about such issues.
The object of the Symposium on Comprehensive Force Protection
is to "promote the development and dissemination of comprehensive force
protection technology and methodology for the built environment."
No doubt symposium attendees will be
listening with a renewed appreciation for the reality of the threats
and the importance of architectural protection. As Pentagon renovation
manager Evey grimly concluded, "that the [terrorists] happened to hit
an area that we had built so sturdily was a wonderful gift."
B.J. Novitski is managing editor for ArchitectureWeek.