Large buildings, tall chimneys, smokestacks, and increasingly some smaller structures may
be destroyed by building implosion using explosives. Imploding a building is very fast and an expert
can ensure that the building falls into its own footprint, so as not to damage neighboring structures.
Implosion techniques can be applied on masonry structures, reinforced concrete structures, steel
structures, and composite structures. On the contrary of the true implosion, building implosion
techniques do not rely on the difference between internal and external pressure to collapse a
structure. Instead, the technique weakens or removes critical supports so that the building can no
longer withstand the force of gravity and falls under its own weight.
The mechanism of collapse of the towers of the World Trade Center WTC is of interesting
matter and investigation that is more precise should be implemented to understand how those towers
were collapsed. The present study provides an attempt to understand the mechanism of the collapse
or demolition of the north tower WTC1from the structural point of view. Analytical modeling
comprising the sound and damaged building was considered. Wind load, impact load, temperature
effect, and combinations of different loads were taken into account. Digital Image Analysis DIA of
documented video was very helpful when its results are related to the results of the analytical study.
The results of the analytical study showed the structural safety of WTC1 against wind load, impact
load and the combination of loads. The overall structural safety of the WTC1 was insignificantly
affected due to hitting of aircraft. The average temperature rise due to the explosion of fuel tank was
about 413ºC. Analysis of the documented video showed that the mode of collapse of WTC1 was
identical to the collapse of buildings demolished using the controlled demolition technique.
Keywords: Controlled Demolition, Thermite, North Tower of World Trade Centre (WTC1),
Digital Image Analysis (DIA), Sound Structure (SS), Damaged Structure (DS).