by Gregory Szuladzin’ ski, Anthony Szamboti and Richard Johns
Reprinted from International Journal of Protective Structures
Volume 4 · Number 2 · June 2013

ABSTRACT
This article elaborates on variables associated with the collapse of the
North Tower of the World Trade Center. The previously published
quantifications of inertia, column capacity, and the assumptions
related to the beginning of downward motion, are examined and
corrected. The reasons for false conclusions reached in several previous
analyses are presented.

1. INTRODUCTION
This presentation is not so much about how the WTC towers failed, but about how they could
not fail. The objective is to eliminate erroneous concepts supported by false assumptions and
by the use of incorrect values for velocity, mass, and column resistance. The only complete
hypothesis of the global collapse mechanism of the Towers is a successive flattening of
stories associated with compressive column failure and referred to as a Progressive Column
Failure mode or PCF in brief. (In the past this mode was often referred to as pancaking, but
this term is not used here to avoid ambiguities). It is explained here why PCF could not be
the mode of the ultimate destruction. The previously published material is quoted and the
new points are brought up. Appendix C can be of interest to those who want a broader
description of facts associated with the collapcollapse. The available information relating to the
kinetics of the collapse is summarized first.

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