Most of us can still remember where we were on that fateful and tragic day of 11 September 2001 when the Twin Towers of the World Trade Centre (WTC) in New York collapsed. Whilst damage to the Twin Towers and the Pentagon were widely reported – what is less well known is the damage to some of the other surrounding buildings including WTC #7.
In particular the collapse of Building 7 has attracted a significant amount of controversy. The National Institute of Standards and Technology (NIST) concluded that fire damage around Column 79 in the north east corner, initiated a progressive collapse mechanism that caused a straight down collapse of WTC#7 into its own footprint. This took place at free fall velocity for the first 32 meters of its descent.
NIST hypothesised this “never seen before” collapse mechanism to explain the collapse thereby making WTC7 the first high rise steel building in history to collapse from fire alone.
Like other steel framed buildings throughout the world, Building 7 was designed by professional engineers to withstand normal office fires. If the design was indeed at fault, significant changes should be made to steel building design, construction and maintenance standards. But since the NIST report was issued in 2008, NIST’s own records show that the ICC (International Code Council) has not addressed the root causes put forward.
In March 2020 the University of Alaska Fairbanks (UAF) published a report following a detailed four year investigation into the WTC7 collapse. The UAF study ran a multitude of static and dynamic analysis simulation cases to find a scenario that best matched the observed collapse, including those proposed by NIST. Unlike NIST the UAF study found a scenario that exactly matched the observed collapse both visually and in the time domain – a scenario and conclusion that is very different from the official narrative. In the interests of public safety we need to understand the true cause of this event, so appropriate action and evacuation philosophies can be implemented in similar buildings.
With this in mind the IMechE Construction and Building Services Division (CBSD) has set up a Technical Advisory Committee (TAC) to look into the findings of the UAF report and see if they have any merit.