Yes, gravity is always present but nobody blames gravity when you drop something. Then you have to study both objects involved at contact and see what happens.
I'll repeat Pixy Mixa here. Without gravity the object will not fall. It is gravity that provides the energy to the interaction between the object and the floor when that object is dropped on the floor.
You cannot, like Bazant, Nist & Co, assume that the smaller object, the WTC1 upper part, is rigid while the bigger object is weak, etc. That is cheating from the start.
I do not assume the upper section of the building is ridged as a structural whole. I am more concerned with the mass and momentum of the upper floors. Even if the structures of the upper section of the building were completely disarticulated the aggregate or combined mass of the upper section is still there and it is still in motion. This point will become clearer below with a picture I will attach
In this case the smaller object has exactly the same structure as the bigger object, i.e. an assembly of strong columns, weaker beams and thin concrete floor slabs. Not rigid at all!
But the individual parts of the structure will still contain some ridgitiy as in the columns. I will explain more toward the end of this post.
And when the smaller object contacts the bigger objects there are serious local failures at points of contacts due to the high pressures developing there. The energy applied is transformed into all these failures ... and that's it.
No, that is not quite it. You are assuming that all of the energy is being expended at one time by the failures. You are forgetting that gravity is still appling potential energy to all the parts that have undergone structural failure and those parts will go on to impact and cause damage to other structures.
If the part has failed to the point that it has become disarticulated or disconnected from its support structure it is free to move. Gravity will continue to pull the newly freed object downward to impact the structures below it. And remember that the debris that damaged that newly freed structure is also still in motion. It still has momentum/potential energy due to it's position in a gravitational field in refrence to the ground.
The worst that can happen is that the complete smaller object is destroyed while the bigger object is just partially damaged.
No, the worst that can happen is a cascade failure as the smaller object cause parts of the larger structure to disarticulate and impact further structures farther on down which causes them to become disarticulate also and so on and so on.
Its like knocking over bowling pins but verticaly. You knock over the single pin at tha apex of the arrangment and it falls and knocks over two pins and those two pins each knock over two other pins and so forth untill all the pins are knocked down. And all this from just pushing over one single pin. Knocking down dominoes is another example.
Actually, it is the stronger parts of both objects, the columns, that will damage the weaker parts of both objects, beams and floor slabs, and after a while the weaker damaged parts get entangled into one another and friction between these parts starts to play its role.
Agreed. It is the columns that have become the most damaging projectiles in the structure. They would act like the shot in a shot gun cartridge.
Again you are forgeting about gravity/potential energy and the nature of the structures and the failures. All the columns do not fall and impact at the same time so alot of the energy and damage will be spread out and accumulate over time. A structure may be able to with stand a single column impact, but it may not hold up to the impacts of the other columns in the upper parts of the upper structure as it falls or moves into the structure below it..
To suggest that the smaller object (read assembly of parts) can completely destroy the bigger object is just fantasy and has nothig to do with physics or gravity.
Wrong, it has everything to do with physics and in this case gravity. There is such a thing as cascade failure, or rather catastrophic failure.
http://en.wikipedia.org/wiki/Catastrophic_failure
It is interesting to note that Bazant, Nist & Co regard the smaller object not only as rigid but also as solid, with uniform density, inflexible, undestructible, etc, etc. It has nothing to do with reality.
More than likely not, but think it had more to do with simplification and explination rather than analysis.
Same thing with WTC7. Nist suggests that if you pour diesel oil in the basement and ignites it, the whole 47 storeys structure above suddenly collapses. Just fantasy; the diesel oil just burns on the floor (actually it is the gas of the diesel above the oil that burns) and most heat is just vented away with the smoke. Local heating of structure in the ceiling will be small and all parts will thermally expand and any local failures will be minor. The columns are spaced far apart and will not heat more than a couple of hundred degrees = no problem. Just ask NYFD and they will confirm it. Or do my experiment at
http://heiwaco.tripod.com/nist1.htm#6 .
If I am not mistaken, I think that NIST found that the the collapse of WTC 7 was more due to key structural damage by falling debris from WTC 1 or 2 than the diesel fire. I could be wrong though. I haven't finished reading it.
Anyhoos there is acouple of problem with your assesment. The fire is in an enclosed space. thermal effects will be greater than in a open area. Since the area is enclose the smoke will make contact with more surfaces and transfer it heat to those structures on it way out of the enclosed structure.
Also if the fire is spread over a large surface area more structures will be affected. Heat expansion will cause deformation and displacement. And heat will cause steel to loose some of it's strength. Steel does not have to melt to fail.
Please, come up with a better argument than that I have no idea about physics and structural engineering.
Well, you certainly seem to be overlooking quite a few aspects of the physics of the collapse.
Here is something I wanted to point out. Take a look at athe picture below (or above) notice the building that I circled. Notice the massive holes in the building. Those were made by not by the entire upper structure of the WTC but by the debris that fell on it. Notice how the roof stuctures were knocked loose and impacted the structures below along with the debris that knocked the roof structures in the first place.
Did the debris that struck and knock down the roof section expend all of its energy hitting and damaging the roof? or did gravity also cause that initial debris to also fall into the structurs below?
So how much mass impacted the structures below the roof? Just the roof structures or the roof + initial impacting debris?
Also think about what would have happened to the building if there were a falling debris field that covered the entire area of the building. Probably be considerably less of the structure still standing if any at all.
Now Think about when the upper section of the WTC started to fall into the structures below. It looks to me like it coverd the entire area of the floor below?
When all that moving debris impacted on the floor below would there not be more than sufficient energy to completly disarticulate the structures of that floor? would all that newly disarticulated debris now then impact the floor below along with all the mass of the upper structure that initially started to fall?
I hope you are begining to see my point.
