ENGLISH VERSION 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 Twin Towers(World Trade Center 1), proposed by the National Institute of Standards and Technology (NIST), with thefundamental principles of classical mechanics. The analysis is structured in two phases: (1) quantitativeassessment of the thermal weakening of the structure due to fires, and (2) energy balance of theprogressive collapse.The thermal analysis demonstrates that, considering the total mass of structural steel (»100,000 tonnes)and the total energy released by the fires (~1013 J), the average temperature increase of the entirestructure is between 40°C (realistic scenario) and 200°C (unrealistic limit scenario with 100% energytransfer to the steel). Such temperatures are insufficient to cause significant structural weakening at aglobal level.The energy balance of the collapse reveals a fundamental inconsistency: the gravitational potentialenergy available at the first impact (2.9 GJ for an 18-floor block falling 3.7 m) is sufficient to destroy atmost 5–6 floors, assuming a conservative destruction energy of 0.5 GJ per floor. The study concludesthat the progressive gravitational collapse model does not satisfy the constraints imposed by energyconservation and the mechanics of variable-mass systems, and does not provide a physically coherentexplanation of the observed event.