ENGLISH - Critical Verification of the Progressive Gravitational Collapse Model World Trade Center 1

This study analyses the compatibility of the progressive gravitational collapse model of the TwinTowers (World Trade Center 1), proposed by the National Institute of Standards and Technology(NIST), with the fundamental principles of classical mechanics. The analysis is structured in twophases: (1) quantitative assessment of the thermal weakening of the structure due to fires, and (2)energy balance of the progressive collapse.The thermal analysis demonstrates that, considering the total mass of structural steel(approximately 100,000 tonnes) and the total energy released by the fires (~1013 J), the averagetemperature increase of the entire structure ranges between 40°C (realistic scenario) and 200°C(unrealistic limit scenario assuming 100% energy transfer to the steel). Such temperatures areinsufficient to cause significant structural weakening at a global level.The energy balance of the collapse reveals a fundamental inconsistency: the gravitational potentialenergy available at the first impact (2.9 GJ for a block of 18 floors falling 3.7 m) is sufficient todestroy at most 5–6 floors, assuming a conservative destruction energy of 0.5 GJ per floor. Thestudy concludes that the progressive gravitational collapse model does not satisfy the constraintsimposed by energy conservation and the mechanics of variable-mass systems, and does notprovide a physically consistent explanation of the observed event.