09-08-2013, 08:02 PM
First thanks for attempting to make sense of my cartoon. It's a cartoon and obviously not a depiction of the actual dynamics but suggests/shows how the gavity forces work as the structure degrades.
axial strength refers to the ability of a column to resist or support loads applied directly above (compression)
A column's axial strength is limited by its slenderness ration.. stout columns are stronger then slender ones. Too slender will buckle from their own weight.. meaning that as the unbraced length increases... a given column section weakens ie supports less load and thus is more subject to buckling (failure)
The arrows are meant to indicate the direction of the loads...
When a column is removed if a multistory structure the column above it has no support and can't couple the forces (loads) to the foundation and the earth. These loads are then redistributed to columns that are coupled. The load has not changed... it has to and does find other paths.
you weigh 100 pounds and when standing each food supports 50 pounds. If you stand on a scale with both feet it shows 100. If you lift one foot it STILL shows 100 because all the 100 pounds are resisted by one leg.
Now if you lift the heaviest thing you can... say your dog which weighs 50#... each leg is at its limit of 75 pounds. On the scale it shows 150.
If you try to stand on one leg... you collapse... your leg would *buckle* at the knee and you'd call down and you would likely fall in the direction of the missing or lifted leg.
The twin towers had many columns and they shared the load carrying and when the columns were destroyed and weakened the load sharing was shifted all about. This caused uneven stresses and even warping, torquing and distortion and eventually collapse when the capacity was eroded below loads imposed. The failure rapidly propagates one this happens... the structure does not fall at once... but the propagation can be very quick when as more and more load is carried by fewer and fewer columns. This also introduces some eccentricity and tilt of the falling top... as it's almost impossible to have a completely symmetrical force/load redistribution.
We know the core collapsed first because we see the antenna begin to sink into the top... and this was followed by the release but inside the entire core up there and the floors were already probably dropping. The facade hung together because of the nature of the structure... structures without internal stress do not fall apart or even distort... they sort of float (as in free fall) When they meet resistance or forces they yield to them in some manner.
The disconnected mass of the top floors is what drives down through the tower destroying it.
axial strength refers to the ability of a column to resist or support loads applied directly above (compression)
A column's axial strength is limited by its slenderness ration.. stout columns are stronger then slender ones. Too slender will buckle from their own weight.. meaning that as the unbraced length increases... a given column section weakens ie supports less load and thus is more subject to buckling (failure)
The arrows are meant to indicate the direction of the loads...
When a column is removed if a multistory structure the column above it has no support and can't couple the forces (loads) to the foundation and the earth. These loads are then redistributed to columns that are coupled. The load has not changed... it has to and does find other paths.
you weigh 100 pounds and when standing each food supports 50 pounds. If you stand on a scale with both feet it shows 100. If you lift one foot it STILL shows 100 because all the 100 pounds are resisted by one leg.
Now if you lift the heaviest thing you can... say your dog which weighs 50#... each leg is at its limit of 75 pounds. On the scale it shows 150.
If you try to stand on one leg... you collapse... your leg would *buckle* at the knee and you'd call down and you would likely fall in the direction of the missing or lifted leg.
The twin towers had many columns and they shared the load carrying and when the columns were destroyed and weakened the load sharing was shifted all about. This caused uneven stresses and even warping, torquing and distortion and eventually collapse when the capacity was eroded below loads imposed. The failure rapidly propagates one this happens... the structure does not fall at once... but the propagation can be very quick when as more and more load is carried by fewer and fewer columns. This also introduces some eccentricity and tilt of the falling top... as it's almost impossible to have a completely symmetrical force/load redistribution.
We know the core collapsed first because we see the antenna begin to sink into the top... and this was followed by the release but inside the entire core up there and the floors were already probably dropping. The facade hung together because of the nature of the structure... structures without internal stress do not fall apart or even distort... they sort of float (as in free fall) When they meet resistance or forces they yield to them in some manner.
The disconnected mass of the top floors is what drives down through the tower destroying it.