Buildings are not specifically designed to withstand the impact of fuel-laden commercial airliners. While documents from The Port Authority of New York and New Jersey (PANYNJ) indicate that the impact of a Boeing 707 flying at 600 mph, possibly crashing into the 80thfloor, was analyzed during the design of the WTC towers in February/March 1964, the effect of the subsequent fires was not considered. Building codes do not require building designs to consider aircraft impact.
The load conditions induced by aircraft impacts and the extensive fires on September 11, 2001, which triggered the collapse of the WTC towers, fall outside thenorm of design loads considered in building codes.
Seems to contradict the claim that the towers could withstand an explosive strike from a 707 travelling at 600mph.
Fires played a major role in further reducing the structural capacity of the buildings, initiating collapse. While aircraft impact damage did not, by itself, initiate building collapse, it contributed greatly to the subsequent fires and the thermal response of the structuresby:
•Compromising the sprinkler and water supply systems;
•Dispersing jet fuel and igniting building contents over large areas;
•Creating large accumulations of combustible matter containing aircraft debris and building contents;
•Increasing the air supply into the damaged buildings that permitted significantly higher energy release rates than would normally be seen in ventilation limited building fires, allowing the fires to spread rapidly on multiplefloors;
•Damaging and dislodging fireproofing from structural components in the direct path of the debris and due to the strong vibrations generated by aircraft impact; and
•Damaging ceilings that enabled “unabated” heat transport over the floor-to-ceiling partition walls and to structural components.
Nowhere does it say that only fires caused the collapsed of the towers, but the combined structural damage and the ensuing fires. It specifically says the airplane strike contributed to the collapse.
Probable Collapse Sequence for WTC 1
1.Aircraft Impact Damage:
•Aircraft impact severed a number of exterior columns on the North wall from floors 93 to 98, and the wall section above the impact zone moved downward.
•After breaching the building’s perimeter, the aircraft continuedto penetrate into the building, severing floor framing and core columns at the North side of thecore. Core columns were also damaged toward the center of the core and, to a limited extent on the South side of the core. Fireproofing was damaged from the impact area to the South perimeter wall, primarily through the center of WTC 1 and at least over a third to a half of the core width.
•Aircraft impact severed a single exterior panel at the center ofthe South wall between floors 94 and 96.
•The impact damage to the exterior walls and to the core resultedin redistribution of severed column loads, mostly to the columns adjacent to the impact zones. The hat truss resisted the downward movement of the North wall, and rotated about the East-West axis.
•As a result of the aircraft impact damage, the North and South walls each carried about 7 percent less gravity loads after impact, and the East and West walls each carried about 7 percent more loads. The core carried about 1 percent more gravity loads after impact.
2.Effects of Subsequent Fires and Impact Damaged Fireproofing:
A.Thermal Weakening of the Core:
•The undamaged core columns developed high plastic and creep strains over the duration the building stood, since both temperatures and stresses were high in the core area. The plastic and creep strains exceeded thermal expansion in the core columns.
•The shortening of the core columns (due to plasticity and creep)was resisted by the hat truss which unloaded the core over time and redistributed loads to perimeter walls.
•As a result of the thermal weakening (and subsequent to impact and prior to inward bowing of the South wall), the North and South walls each carried about10 percent more gravity loads, and the East and West walls each carried about 25 percentmore loads. The core carried about 20 percent less gravity loads after thermal weakening.
B.Thermal Weakening of the Floors:
•Floors 95 to 99 weakened with increasing temperatures over time on the long-span floors and sagged. The floors sagged first and then contracted due to cooling on the North side; fires reached the South side later, the floors sagged, and the seat connections weakened.
•Floor sagging induced inward pull forces on the South wall columns.
•About 20 percent of the connections to the South perimeter wall on floors 97 and 98 failed due to thermal weakening of the vertical supports.
C.Thermal Weakening of the South Wall:
•South wall columns bowed inward as they were subjected to high temperatures and inward pull forces in addition to axial loads.
•Inward bowing of the South wall columns increased with time.
3.Collapse Initiation
•The inward bowing of the South wall induced column instability, which progressed rapidly horizontally across the entire South face.
•The South wall unloaded and tried to redistribute the loads via the hat truss to the thermally weakened core and via the spandrels to the adjacent East and West walls.
•The entire section of the building above the impact zone began tilting as a rigid block (all four faces; not only the bowed and buckled South face) to the South (at least about 8º) as column instability progressed rapidly from the South wall along the adjacent East and West walls.
•The change in potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.
Here is the report that you say supports your claims. Show me where.