|
|
||
|
|
|
|
The photograph is from:
http://www.debunking911.com/collapse.htm
Question by David Bushnell:
Even after all these years since 2001, the question remains: “What local structural failure about an hour after initial impact precipitated global collapse of the building?” Did local plastic buckling of the hot columns of the outer wall over a height of one or more floors at and near the location of initial impact initiate global collapse? Or did sagging of the hot floor joists (trusses) at the most critical floor cause local failure where the floor joists are seated at the outer wall and/or at the core structure, causing all or part of that floor to crash onto the floor below, giving rise to detachment of the ends of the floor joists from their seats on that lower floor, and so on, floor after floor? Or did some combination of these initial failures occur? Here the top part of WTC2 seems to tilt as a rigid body, indicating that initial collapse occurred only on the initially impacted face.
This and the next several slides do not answer these questions but show the viewer some details of the structure that failed, give an idea of the types of analyses performed, and provide a few comments by researchers.
Text from:
http://www.inderscience.com/offer.php?id=47711
Temporal considerations in collapse of WTC Towers, by Gregory Szuladziński International Journal of Structural Engineering (IJSTRUCTE), Vol. 3, No. 3, 2012
ABSTRACT: The circumstances leading to the collapse of the WTC Towers were described in numerous publications before but quantification of possible mechanisms published so far remains very limited. The basic observation is that columns of a 110-story building were weakened, over a relatively short segment of an upper part of the structure, to a degree where they were unable to support the building above them. As the upper part began to descend, successive buckling of columns caused flattening of the stories below. The process was presumably driven by the action of gravity until a complete destruction of the building. This article concentrates on progressive collapse of the core of the building. Several mechanisms are considered and quantified, to assess whether they offered a plausible explanation. One of the criteria used was whether the potential energy available was sufficient to cause the demolition in the assumed manner. The calculated duration of the event versus the available observation is regarded as the main criterion to qualify the postulated collapse mode. The details presented here are in reference to the North Tower [WTC1]. Some relationships presented here are also useful for a progressive collapse analysis of reinforced concrete structures.
Text from:
https://911inacademia.files.wordpress.com/2011/01/preview-some-misunderstandings-of-wtc-collapse-analysis.pdf
“Some Misunderstandings Related to WTC
Collapse Analysis”, by Gregory Szuladzinski, Anthony Szamboti, and Richard Johns, International Journal of Protective Structures, Vol. 4, No. 2, 2013.
ABSTRACT: This article elaborates on variables associated with the collapse of the North Tower [WTC1] 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.
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.
Page 58 / 114