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Why would you make a floor hanging off the vertical columns at the 12th floor more massive than the 105th floor hanging off the vertical columns?
The columns got bigger/ stronger closer to the ground...
The sections of the towers above the impact locations fell apart/turned to dust as they fell and before they hit the ground...
The falling weight from above was constantly being reduced as the collapse progressed... So how could it "pile drive"?
But the connections that held each floor was identical.
Pulverized concrete and drywall has the same mass as solid.
Not all floors, the mechanical floors contained solid steel-framed supports.
The rest of the floor diaphragms consisted of lightweight concrete slabS poured onto corrugated steel pans,
All floor systems got lighter towards the top".
Are you saying the mechanical floors had more mass then the “lightweight concrete slabs?
ws680.nist.gov...
There were four major structural subsystems in the towers: the exterior wall, the core, the floor system, and the hat truss. The structural design team incorporated a framed-tube concept for the exterior structural system. Columns supporting the building were located both along the
external faces and within the core. The core also contained the elevators, stairwells, and utility shafts. The dense array of columns along the building perimeter resisted lateral wind loads, while also supporting the gravity loads about equally with the core columns. The floor system provided stiffness and stability to the framed-tube system in addition to supporting the floor loads.
The first major structural subsystem was the exterior framing, which was a vertical square tube that consisted of 236 narrow columns, 59 on each face from the 10th floor to the 107th floor (Figure 3). There were fewer, wider-spaced columns below the 7th floor to accommodate doorways. There were also columns on alternate stories at each of the beveled corners, but these did not carry gravity loads. Each column on floor 10 to 107 was fabricated by welding four steel plates to form a tall box, nominally 0.36 m (14 in) on a side. The space between the steel columns was 0.66 m (26 in), with a framed plate glass window in each gap. Adjacent columns were connected at each floor by steel spandrel plates, 1.3 m (52 in) high. The upper parts of the buildings had less wind load and building mass to support. Thus, on higher floors, the thickness of the steel plates making up the columns decreased, becoming as thin as 6 mm (1⁄4 in) near the top down from as thick as 76 mm (3 in) at the lower floors. There were 10 grades of steel used for the columns and spandrels, with yield strengths ranging from 248 MPa (36 ksi) to 690 MPa (100 ksi). The grade of steel used in each location was dictated by the calculated stresses due to the gravity and wind loads. All the exterior columns and spandrels were prefabricated into welded panels, three stories tall and three columns wide. The panels, each numbered to identify its location in the tower, were then bolted to adjacent units to form the walls (Figure 4). Field panels were staggered so that every third panel was spliced at each floor level. The use of identically shaped prefabricated elements was an innovation that enabled rapid construction.
The second structural subsystem was a central service area, or core (Figure 3), measuring approximately 41 m by 26.5 m (135 ft by 87 ft), that extended virtually the full height of the building. The long axis of the core in WTC 1 was oriented in the east-west direction, while the long axis of the core in WTC 2 was oriented in the north-south direction. The 47 columns in this rectangular space were fabricated using primarily 248 MPa (36 ksi) and 290 MPa (42 ksi) steels and decreased in size at the higher stories. The four massive corner columns bore nearly one-fifth
of the total gravity load on the core columns. The core columns were interconnected by a grid of conventional steel beams to support the core floors.
The third major structural subsystem was the floors in the tenant spaces between the exterior walls and the core. These floors supported gravity loads, provided lateral stability to the exterior walls, and distributed wind loads among the exterior walls. With the exception of the mechanical floors (Floors 7, 8, 41, 42, 75, 76, 108, and 109) which had rolled structural steel shapes, tenant floors had truss systems. As shown in Figure 5, each tenant floor consisted of 102 mm (4 in) thick, lightweight cast-in-place concrete on a fluted steel deck. Supporting the slab was a grid of lightweight steel bar trusses. The top bends (or “knuckles”) of the main truss webs extended 76 mm (3 in) above the top chord and were embedded into the concrete floor slab. This concrete and steel assembly thus functioned as a composite unit, that is, the concrete slab acted integrally with the steel trusses to carry floor loads. Without the presence of the knuckles (or the shear studs in WTC 7), the floor slab and trusses (or beams) would have acted independently, resulting in reduced load capacity. The primary truss pairs were either 18.3 m (60 ft) or 10.7 m (35 ft) long and were spaced at 2 m (6.7 ft). There were perpendicular bridging trusses every 4 m (13.3 ft). The floor trusses and fluted metal deck were prefabricated in panels that were typically 6.1 m (20 ft) wide and that were hoisted into position in a fashion similar to the exterior wall panels.
Not all floors, the mechanical floors contained solid steel-framed supports.
The trusses were not just connected by a couple of bolts to the perimeter walls....the truss ends rested on steel plates that were both welded and bolted to the top chords of the trusses and attached via bolted damping units to their lower bottom chords.