There were no normal fires present and very little evidence of conventional heat; note the millions of unburnt paper. Most of the buildings, including the steel and the most of the people inside, turned to dust leaving very little rubble or seismic impact. Dustification is a term first coined by Dr. Judy Wood to describe this new phenomenon. In fact, the rubble were still dustifying for months and even years afterwards, which is indicative of continually molecular breakdown.
NIST even had conducted fire experiments and which as expected hardly any damage was done to the building structure: