How tall towers can be brought down

“Bending and buckling (deformation) of steel beams and columns occurs when the steel temperature exceeds approximately 538 degrees C (1000 degrees F). At elevated temperatures, steel exhibits a progressive loss of strength. When there is a greater fire exposure, the load required to cause deformation is reduced. Deformation is not the result of melting. A deformed element is not one that has melted during the fire, and therefore the occurrence of such deformation does not indicate that the material was heated above its melting temperature.” – Technical Committee on Fire Investigations, Sec. 6.2.9.1, NFPA 921 Guide for Fire and Explosion Investigations (2011 Edition)