The collapse of WTC 1&2 was correct in sequence and action, and now looking at the type of support beams and vertical inner and outer structure, I see nothing out of the ordinary in how it collapsed.
The main support was at the Central core of the structure, was a long rigid Central spike, and every thing was attached to it, and then radiated out to the outer supports which were were lite corrugated steel support beams, creating a outer skin or rind.
The Central core structure
Typical Floor Plan of the World Trade Center:
A perimeter of closely spaced columns, with an internal lift core. The floors were supported by a series of light trusses on rubber pads, which spanned between the outer columns and the lift core.
The Central Core vertical support structure, acted as the guide running straight up the center of the top section of the WTC towers, this guided the upper structure straight down.
The radial support were of light corrugate beam material, that once it was kinked, bent, or twister lost it's load bearing ability, even with out heat induced lose of tensile strength.
The Outer vertical support was was corrugated beam, that one it is out of alignment with it's self, due to kinking, bending, twisting, has no structure support strength.
The horizontal beams were sheared at the ends, sheared from the Central Core, and sheared at the wall supports, the action very much like a Pineapple corer in action.
It was a giant impalement, the Central core acting as the spear impaling the Upper Structure through the Upper Central Core structure.
Once the Upper Structure is in motion, add Newtons Laws, and :
Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination. Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards. Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete story at the level of impact.
Once one story collapsed all floors above would have begun to fall. The huge mass of falling structure would gain momentum, crushing the structurally intact floors below, resulting in catastrophic failure of the entire structure
As can be seen Perimeter columns, several stories high, and still linked together, were pealed from the Towers like the rind of a Pineapple.
Not only is the floor directly below the collapse point destroyed, but the energy transfer, then is transferred to floors below the collapse point, destroying supporting structure by shock, and creating damage to facilitate the collapse of those floors when the event front impacts them.
The gigantic impact forces caused by the huge mass of the falling structure landing on the floors below travelled down the columns like a shockwave faster than the entire structure fell. The clouds of debris coming from the tower, several storeys below the huge falling mass, probably result from the sudden and almost explosive failure of each floor, caused by the "shockwave".