Abstract
In this
paper, several numerical simulations of framed
structures were performed
to identify the specific structural cause
of the high-speed total collapse of the World Trade Center (WTC) towers, which occurred during the 9/11 terrorist attacks. A full-scale aircraft impact simulation of the WTC tower 2 was conducted to examine the dynamic
unloading phenomena that occurred in the core columns during impact, which may have caused the
destruction of the splices
between column sections. Fire-induced progressive collapse
analyses of a high-rise
tower with an outrigger
truss system were carried out to qualitatively demonstrate the
effects of fire patterns and structural parameters on the behavior of this
tower’s collapse. In general, the tower remained standing for a longer period of time due to the catenary action of the
outrigger truss system only if the load paths in the tower were protected and if the member
connections were strong enough. However, in these analyses, the collapse speed never reached a value as
high as that of the free fall observed in the WTC collapse, which occurred while
the splices between
column sections still retained their tensile strength. From these
results, it is evident that the high-speed collapse of
the WTC towers might
have been caused by an inherent weakness in their member
connections in addition to the destruction directly caused by the aircraft
impact.