>>13630695To answer your question:
-Steel on the towers was under tensile and compressive stresses
-These stresses resulted in no deformation at room temp
-Once heated, the ductility(lack of resistance to deformation)of the steel begins to rise
-As the steel deforms, it quickly reaches ductile failure (think pulling apart a melty snickers bar) point resulting in the literal dropping of MASSIVE amounts of material on the support structures below it
-The momentum acquired by the falling material results in a devastating amount of force applied to metal that was never rated, designed, engineered, structured, etc... to support it
-The lower floors collapse in turn, each iteration adding to the material falling and force being applied to the subsequent floor.
