9/11 -The collapse of the WTC Twin Towers: the scientific conclusions

After the tragic collapse of the Twin Towers on September 11th 2001, the National Institute of Standards and Technology (NIST), was commissioned to investigate the failure of the two towers  to withstand the hijacked aircrafts’ crashes. The conclusion of their scientific investigation led to modifications of building codes intending to make them more fireproof. Nevertheless, a large group of mechanical engineers and architects from the US contest the scientific results. They ask for a new and independent study of the case and support the conspiracy theory.

After the tragic collapse of the Twin Towers on September 11th 2001, the National Institute of Standards and Technology (NIST) was commissioned to investigate the failure of the two towers to withstand the hijacked aircrafts’ crashes. The conclusion of their scientific investigation led to modifications of building codes intending to make them more fireproof. Nevertheless, a large group of mechanical engineers and architects from the US contest the scientific results. They ask for a new and independent study of the case and support the conspiracy theory.

 

UA Flight 175 hits WTC south tower source : http://upload.wikimedia.org/wikipedia/commons/8/8a/UA_Flight_175_hits_WTC_south_tower_9-11_edit.jpeg
9/11 terrorist attack

 

The fall of the Twin Towers

The World Trace Center (WTC) Twins Towers were 417 and 415 meters high on a ground surface of 4000 m2 and both had 110 floors. The north tower was topped by a supplementary 110 meter high antenna. After the catastrophe of the September 11th, the U. S. Congress commissioned NIST to investigate the cause of the collapse of the WTC towers in order to better understand what happened and to modify skyscrapers’ building codes to prevent similar tragedies in the future. In 2005, NIST released a preliminary report. This was completed in 2008 and a final report including the analysis of the collapse of WTC7 tower, was released.

 

Firstly, the crash of the aircrafts led to the partial destruction of one of the buildings’ façade and damaged some core pillars of the structure. Secondly, the kerosene contained in the wings of the aircraft exploded at the very heart of the buildings.

WTC aerial view source: http://upload.wikimedia.org/wikipedia/commons/7/75/Wtc_arial_march2001.jpg
World Trade Center

 

Following the crashes, fires started in both towers. In the north tower, 6 to 7 floors caught fire. The floors were composed of open work space. The steel structure of the WTC buildings’ floors was protected against fire with fire-resistive materials or rigid fire-rated gypsum panels, both preventing excessive temperature rise in the steel. Unfortunately, according to NIST report 1-6A 2005, the fires and the explosions damaged the passive fire protections of the exposed floors.

The two towers were stable for some time but, in the end, they fell down after 56 minutes and 102 minutes of fire respectively. Simulations showed that in some places, the steel temperature was up to 600, 700 or even 800°C; hence causing the steel to lose most of its resistance and rigidity. Under the effect of temperature, some linking posts between the floors collapsed and the external posts on the façade, caught fire.

Several studies discussed different theories about the precise causes of the collapse, all concluding that the weakening of floors links and the destructions due to the aircrafts’ impacts, were enough to make several floors collapse.

 

WTC7: the third tower

WTC7 was a smaller building of 173 meter high (47 floors) situated 110 meter away from the north tower. Its facades were damaged by debris from WTC1 and several floors caught fire. The fire propagated surprisingly fast and the WTC7 collapsed 7 hours after the start of the fire. The collapse started from the bottom of the building and was suspected to be due to the thermal dilatation of structural posts.

 

WTC fumes on 9/11 source: wstera2/Flickr
New York

 

Some US engineers contest NIST scientific conclusions

The sudden collapse of WTC7 was very surprising for non-specialists. Moreover, the speed of the collapse of the Twin Towers and the fact that they collapsed vertically, even though one of the towers started to bend sidewards, further  raised suspicions. Non-specialists as well as some scientists have questioned this event. The 9/11 Truth Community is an association of architects, engineers…, that claims to “reveal truths about the ‘collapses’ of the 3 World Trade Center high-rises on September11, 2001”.

 

Wreckage from WTC towers source: Ben Sutherland/Flickr
Wreckage from WTC towers

 

They rebut the conclusions of NIST scientific report and they claim that it were explosives (or incendiary engines) that made the floor linking posts collapse. No articles were published in peer-reviewed journals on those conspiracy theories. The 9/11 Truth community principal leader only published one article [Jones, 2008] that asks for more independent studies.

 

 

In conclusion, although most of the evidences of the collapse were destroyed (cement, structure…), analysis of the remains of the building were completed by numerical models and in-conditions testing. Both the collapse of the Twin Towers and the WTC7 were investigated. The conclusions of NIST report enhanced a major failure of the fireproofing system of the Twin Towers floors. It showed that the destruction of some floors led to the collapse of the entire buildings. Although some people request for new studies and denounce the presence of explosives in the buildings prior to the aircrafts crashes, no official sources or scientific publications support those controversial theories.

Such a tragedy that has shaken the entire world was bad enough without a conspiracy being behind it. This tragic event should be remembered for the implications it has had on our western civilizations and on the international relations but it is also good that science studies the collapse of the buildings so as to improve building construction in the future.

  Similaire articles on MyScienceWork: Complex Systems and the Number of Deaths in Iraq and Afghanistan Systèmes complexes et nombre de morts en Irak et Afghanistan Source: Effondrement des tours du WTC: les conclusions scientifiques…, J. Quirant, 2009, http://www.bastison.net/ZIDEOS/AUGC09_04-21_QUIRANT.pdf World Trade Center Disaster Study by NIST, http://www.nist.gov/el/disasterstudies/wtc/ Jones S. E., Legge F. M., Ryan K. R., Szamboti A. F., Gourley J. R., “Fourteen points of agreement with official government reports on the World Trade Center destruction”, The open civil engineering journal, Volume 2, 200   En savoir plus : Attentats du 11/9 : Mythes et Légendes, http://www.bastison.net/ Zéro pointé pocket : Critique technique de la vidéo « Zero », http://www.bastison.net/RESSOURCES/Zero_Pointe_Pocket.pdf