Assessment of structural steel from the World Trade Center towers, part II: Analysis of images for forensic information

摘要

A meaningful modeling analysis of the collapse of the World Trade Center towers required documentation of the damage of the buildings due to the aircraft impacts. Images accumulated during the National Institute of Standards and Technology National Construction Safety Team investigation were analyzed for information regarding structural damage and failure modes. A number of recovered and identified components survived the building collapse and subsequent handling during recovery in essentially the same condition as they were post-impact. The modes of failure for bolted and welded connections of the outer wall were documented, as was the condition of the spray-applied fire-resistant material (fireproofing) that had been sprayed onto the structural steel during erection of the building. Finally, images taken of portions of the towers at the locations of identified recovered components were studied to determine whether they were exposed to post-collision fires and to establish the extent of the exposure.