@MastanKhan
Thank you Sir for your detailed response. I have further remarks to your post.
Regarding the projectile thing, everything is possible but what I saw in video was an airplane slicing through the iron mass like a hot knife into butter.
That was as unbelievable stuff, as i may see elephant flying with aid of his ears
'General stuff caught fire' I refer as building fire.
Building fire- i.e. London fire, or any other building around us on fire.
When Building fire is contained in time, either by design or by quick response, i.e. its been put out in 3-4 hours, than surely building has subjected to heat for relative shorter time, than compare to out of control fires, where fire gradually goes down because there's nothing more left to catch fire (no more combustible material).
No sir, concrete cannot catch fire in open air environment.
Concrete always absorb moisture, slowly but permanently. Hence there can't be residual moisture in old buildings, unless water is poured in constantly.
Yet, I don't know what was the volume of concrete in twin tower, sure there was residues of concrete and metal, fused together.
Twin-towers collapsed in matter of minutes, there was such a limited fire and time that it
can't possibly melt huge volume of steel all around, evenly and identically in 3 buildings.
When a design is laid, there are always fuse structures added. In case of steel structures/buildings- joints, rivets, bolts.. can be considered as fuses/weak links.
Floors were spread over light trusses, which should have melted before the gigantic structural columns, which weigh tons and those again are riveted/bolted to each other with stronger elements, while trusses hang on them with relatively weaker joint elements.
In case of over weight, individual trusses should break off from their joints, rather than core structure.
Each building of twin tower, had an inner structure, which was independent of outer structure.
damage to the structure of outer perimeter may not lead to collapse of building. definitely not in free fall.
There were explosions in orderly manner. Those were
definitely not the random explosions of bursting structure or auxiliaries.
Buildings are sealed and insulated from outer environment but they are not airtight.
Fresh air is regulated in buildings, based on temp. humidity and occupancy.
In order to save energy there are heat exchangers available in air-handling units aka AHU.
Glass windows and the cladding, were surely seen blowing outwards, along with concrete pulver. I must admit, I'm not familiar of a fire which can blow away concrete and steel in matter of minutes, and in tuned rhythm !!! There must be a science behind, but I cannot relate it to fire/impact/jet fuel.
Weight of the air craft was fraction of the weight, those buildings were design to bear.
However, each floor have its limit, because of the relatively weaker trusses and their joints.
Your theory is right, in case if whole aircraft is parked on a floor, surpassing the weight limit of that floor, than it must sag or worst fall off. Readily we don't know, what was that limit and the situation was certainly complicated, when fiber/aluminum plane disappeared into various floors of twin tower.
Actually, you raised a good point. Someone should check the aspect ratios of plane and building floors and analyze it.
Sir, try to quiz some of your friendly client who happenz to be a structural engineer or metallurgical engineer.
