World Trade Center Towers: A Structural Autopsy

In a scrap yard across the Hudson River from the fallen twin towers, engineering professor Abolhassan Astaneh-Asl pores over the 1,500 tons of twisted, charred steel arriving here each day from the remains of the World Trade Center like an archaeologist, like a coroner... Astaneh-Asl -- who has had access to 40,000 tons of scrap -- said his findings confirm the widely held theory about the buildings' demise: that the impact of the planes did relatively little damage to the Towers. Rather, it was 1,000-plus-degree heat from the burning jet fuel that caused key outer beams to buckle, and floor after floor to fall."