Renovation Program Had Hardened the Facade Attacked on 9/11/01
The renovation program included the following improvements to the building:
- Exterior walls reinforced with steel
- Exterior walls backed with Kevlar
- Blast-resistant windows installed
- Fire sprinklers installed
- Automatic fire doors installed
- Building operations and control center created
An article in Structure Magazine provided background on the project. It cited the April 19, 1995 bombing of the Murrah Federal Building in Oklahoma City as the motivation for the renovation program. It noted that the original design was constrained by the material demands of World War II.
The steel reinforcements to the walls consisted of tubular frames surrounding the window openings and attaching to the reinforced concrete floor slabs. Each windowed wall panel (between vertical concrete columns) was retrofitted with a piece consisting of two horizontal tubes welded to two vertical tubes running from the floor to the ceiling. 3
|This illustration shows reinforcements added to the Pentagon's walls as seen from the inside. Reinforced concrete columns are shown in gray, and tubular steel reinforcements are pictured in red.|
The reinforcements were to be sequentially applied to the five wedges of the Pentagon over time. Wedge One -- one of five sections of the Pentagon -- was the first to be retrofitted, and the upgrades to the exterior wall were complete by 9/11/01. Wedge Two was apparently yet to be retrofitted. The plane crashed into the building's exterior entirely within Wedge One.
Kevlar cloth was stretched between the steel columns to provide blast resistance to the short spans of brick wall. 4
The original windows were replaced with blast-resistant windows nearly two inches thick.
2. Retrofitting the Pentagon for Blast Resistance, Structure Magazine,
3. Pentagon Battered but Firm, ArchitectureWeek.com, 10/3/01 [cached]
4. Pentagon Battered but Firm, ArchitectureWeek.com, 10/3/01 [cached]