Originally posted by DrEugeneFixer
Originally posted by psikeyhackr
I do not give a damn about those details of structural engineering..
psik
Apparently not, or you would know something more about it by now than what you read on ATS.
Originally posted by psikeyhackr
Structural engineers are just pretending it is complicated...
It's all a plot to make you look dumb.
Have you ever considered that the four "2d arrays of steel arranged perpendicularly" taken along with the slab and truss systems, constitute a "3D array of steel and concrete". Thus, by your own (faulty) logic, it should be able to resist lateral loads.
Originally posted by psikeyhackr
Like I said, SKYSCRAPERS ARE OLD TECHNOLOGY. Trying to make a big deal of structural engineering when the Empire State Building is 80 years old is ridiculous.
Originally posted by psikeyhackr
Laymen are people who can be convinced that they are stupid by people making things unnecessarily complicated.
Originally posted by DrEugeneFixer
Originally posted by psikeyhackr
Like I said, SKYSCRAPERS ARE OLD TECHNOLOGY. Trying to make a big deal of structural engineering when the Empire State Building is 80 years old is ridiculous.
Holding forth on issues you know nothing about-- now that is ridiculous. And it's getting old.
I see that you ignored my point that the perimeter columns, and slabs together comprise a three dimensional arrangement of structural elements. If this is the requirement to resist lateral forces (as your logic implies) then why can't the perimeter columns and floor slabs resist lateral forces?
Keep in mind, I'm only asking this WITHIN the logic that you have laid out.
Originally posted by Darkwing01
Actually, sorry for the mistake, I retract that apology since you kinda failed to meet the terms I offered. Apologies for failing to notice at the time.
"External inputs" are not external to the logic of the model, they are only external to some pre-defined subsystem within the model.
Originally posted by IrishWristwatch
From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force! How the hell does he turn the crank?
Originally posted by snowcrash911
Originally posted by IrishWristwatch
From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force! How the hell does he turn the crank?
I'm sure you meant this in jest, but it needs some clarification: the equal and opposite forces as predicted by Newton's third law do not actually cancel each other out or net to zero force, because they do not act on the same object. E.g. if you push your hand against the wall, the wall pushes back on the hand. Two forces on two different objects. However, without friction with the floor, the person turning the crank would just slide backwards, making his/her force application ineffective.
Originally posted by IrishWristwatch
No, read again. Or read on. When I am talking about the action-reaction pair alone, which is (e.g.) the hand pushing against the wall, the net force IS zero. The equal and opposite forces as predicted by Newton's third law DO cancel each other out to net to zero force, it is the OTHER forces on the body which don't.
To students, it often sounds as though Newton's third law implies nothing could ever change its motion, since the two equal and opposite forces would always cancel. The two forces, however, are always on two different objects, so it doesn't make sense to add them in the first place --- we only add forces that are acting on the same object. If two objects are interacting via a force and no other forces are involved, then both objects will accelerate --- in opposite directions!
(...)
it doesn't make sense to refer to the equal and opposite forces of Newton's third law as canceling. It only makes sense to add up forces that are acting on the same object, whereas two forces related to each other by Newton's third law are always acting on two different objects.
Originally posted by snowcrash911
This also underscores the point about equal and opposite forces not necessarily resulting in equal and opposite damage: slam your hand against the wall hard enough, the forces will be equal and opposite, but your hand will break and the wall will not.
Expand this analogy to two similar objects, e.g. two eggs, drop them onto each other and one might break while the other stays intact, both might break, or none might break.
Bazant postulates a compacted layer of rubble which, as IWW explained, exerts its mass [correction: static weight plus force from change in monentum] on the floors below before [correction: AS] the upper 'block' impacts, then acts as a shock absorber and this somehow prevents the upper block from disintegrating.
This is if I understand it correctly, so correct me if I'm wrong. I'm not saying I agree with Bazant that this is the true, real mode of collapse but as far as I understand it, this is why Newton's Third Law isn't violated in his paper. It's internally consistent in that sense, but that doesn't make it the be all end all of WTC collapse studies.
Newton’s Third Law: The discusser is not correct in repeatedly
claiming that Newton’s third law is violated in the paper
and particularly in concluding that the “two-phase collapse
scenario is scientifically implausible because it ignores
Newton’s third law and the equal but opposite upward force
dictated by it.” As explained at the outset in every course on
mechanics of materials, this law is automatically satisfied,
since all the calculations are based on the concept of stress or
internal force, which consists of a pair of opposite forces of
equal magnitude acting on the opposite surfaces of any imagined
cut through the material or structure. This concept is so
central to the discipline of structural mechanics and self evident
to structural engineers that Newton’s third law is
never even mentioned in publications.
Originally posted by IrishWristwatch
You are correct. Let me quote the bastard, emphasis mine:
Newton’s Third Law: The discusser is not correct in repeatedly
claiming that Newton’s third law is violated in the paper
and particularly in concluding that the “two-phase collapse
scenario is scientifically implausible because it ignores
Newton’s third law and the equal but opposite upward force
dictated by it.” As explained at the outset in every course on
mechanics of materials, this law is automatically satisfied,
since all the calculations are based on the concept of stress or
internal force, which consists of a pair of opposite forces of
equal magnitude acting on the opposite surfaces of any imagined
cut through the material or structure. This concept is so
central to the discipline of structural mechanics and self evident
to structural engineers that Newton’s third law is
never even mentioned in publications.
Critics of Bazant should start by reading Bazant!
Originally posted by snowcrash911
Hmmm, I apologize if I was being a bit dense here, but, I humbly quote my favorite online free physics textbook:
From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force!
To students, it often sounds as though Newton's third law implies nothing could ever change its motion, since the two equal and opposite forces would always cancel. The two forces, however, are always on two different objects, so it doesn't make sense to add them in the first place --- we only add forces that are acting on the same object.