RECENT STRENGTHENING and refurbishment of Washington's Pentagon building reduced the death toll resulting from September's aircraft attack, renovation manager Lee Evey said.
The only wedge to be strengthened so far took the brunt of the Boeing 757 impact.
Addition of steel members, blast resistant windows and bullet-proof textiles saved hundreds of lives by containing the blaze and debris and allowing survivors more time to escape the collapsing structure.
Around 3,500 workers were believed to be in the section of the building hit by the aircraft.
An estimated 124 people are thought to have died.
The aircraft crashed through the first three of the building's five concentric rings, destroying approximately 10% of the structure completely.
A new steel frame had given secondary support to the structure with Kevlar textile stretched between the members inside the walls to contain shrapnel.
The new frame was the only support to the structure after impact. Although this section collapsed after 35 minutes, the delay allowed people to escape.
When constructed in 1942, the five storey Pentagon building was thought to be the largest building in the world.
Each of the building's five sides is 281m long on the outer face and 110m on the inner. It has a 2.4ha central court and a total floor area of over 371,000m 2.A beam and slab reinforced concrete frame was selected to save thousands of tonnes of steel needed for the Second World War. Columns are at 6m centres, with 355mm by 510mm beams.
Floors are typically 135mm thick.
Wall construction consists of two 100mm thick brick inner leafs with a 150mm thick limestone facing.