More WTC Findings

WTC wind load findings (Structural Engineer, November 2004) reports that additional analysis of the original wind load design for the World Trade Center towers has lead to a revision of the National Institute of Standards and Technology's previous findings. According to the revised analysis, the wind loads used in the design of the two towers exceeded code requirements throughout the life of the structures, starting with New York City's pre-1968 code requirements in effect when the buildings were constructed, and including subsequent updated code requirements through 2001, when the buildings were destroyed.

According to the brief article, the new analysis is based on original source documents including wind tunnel testing and wind load estimation methods, as well a revised interpretation of the application of this information. This has lead to an upward revision of the original design loads from earlier preliminary estimates.

Design Flaws did not lead to WTC collapse (Structural Engineer, December 2004) reports on additional NIST interim findings released in late October. Of particular note is a lead investigator S.Shyman Sunder's statement regarding the overall performance of the towers:

The buildings performed as they should have considering the airplane impact and extreme fires to which they were subjected. There is nothing there that stands out as abnormal.

Additional findings included in this NIST report address hypotheses for the causes of the tower collapses, explanation of the differences in survival time between the two towers, assessment of the post-impact capabilities of the towers, the role of fireproofing, the effects of fire on the tower structures, the quality of the structural steel itself, and factors related to occupant egress prior to the collapses.

More info:
NIST's WTC web site