The point is that this happens when the columns have all nearly reached their load limit (some already have been collapsed). All it takes is a final critical column to fail, and the chain reaction proceeds at the speed of ~17,000 feet per second. Spreading out to a 100-foot radius would take about 6 milliseconds before all columns would have failed (every single failure would shift the constant load across a decreasing number of columns, all of which are at the load limit). The compressive failures would be in shear. If the shear is a 45-degree fracture across a 2-foot column, the shear path would be 3 feet and the crack would propagate in 0.176 millisecond. A hundred columns fracturing in series (slowest case) and a load redistribution time of 6 milliseconds would add up to 23.6 milliseconds. The mass of the upper stories is not going to tilt in the span of 20-30 milliseconds. It might shiver, but then it would commence the plunge.
This is the way it works. The loads do not go away. The structural bearing strength of the columns goes away. And when they collectively weaken to their load limit, all it takes is for one column to fail in order to start the devastating chain reaction collapse. How fast do you think loads are transmitted through steel? Any pressure load transmits by sound, and the loads go as fast as sound travels in metal. When a load exceeds the critical strength of a column, how long does it take a crack to propagate? Only at the speed of sound. And then the load-to-bearing ratio simply gets worse with each column failure. There is no dramatic waiting around. Nature operates as fast as it can.
Can demolition crews time their charges to within milliseconds? The clue that you don't "get it," is your ridiculous assertion that a demolition crew would need to destroy only a few columns. As I have clearly explained, the net bearing strength of all columns taken together would have to be reduced to a safety factor of 1, and then all the columns would have to be severed. (Making reference to a failed demolition only says something about failed demolitions. Since there was no demolition, the reference is useless.)
I am an engineer with 3 degrees. In this exchange I have explained matters quantitatively. You have no refutation of this description of what happened, which conforms to the facts and is based on strict scientific principles of failure propagation. You bluster, denounce, deny, accuse, insult, and wish ill upon me. Not the best demonstration of a scientific or truth-seeking spirit.
I've seen this too many times. When the conversation gets to a point where the opponent cannot cope with the technical details or refute them, he resorts to name-calling and condemnation. I think you have outed yourself.
When they don't have a choice, they do. The whole point of a structural collapse is the removal of resistance. An intact building had 1 g of resistance. The structural failure had 0.3 g of resistance. Where else was there to collapse? Spilling down outside of the walls of the lower building? Kind of impossible if the upper structural elements were still intact. Yeah, you tell me what the other path was. I'm waiting.
The point is that this happens when the columns have all nearly reached their load limit (some already have been collapsed). All it takes is a final critical column to fail, and the chain reaction proceeds at the speed of ~17,000 feet per second. Spreading out to a 100-foot radius would take about 6 milliseconds before all columns would have failed (every single failure would shift the constant load across a decreasing number of columns, all of which are at the load limit). The compressive failures would be in shear. If the shear is a 45-degree fracture across a 2-foot column, the shear path would be 3 feet and the crack would propagate in 0.176 millisecond. A hundred columns fracturing in series (slowest case) and a load redistribution time of 6 milliseconds would add up to 23.6 milliseconds. The mass of the upper stories is not going to tilt in the span of 20-30 milliseconds. It might shiver, but then it would commence the plunge.
This is the way it works. The loads do not go away. The structural bearing strength of the columns goes away. And when they collectively weaken to their load limit, all it takes is for one column to fail in order to start the devastating chain reaction collapse. How fast do you think loads are transmitted through steel? Any pressure load transmits by sound, and the loads go as fast as sound travels in metal. When a load exceeds the critical strength of a column, how long does it take a crack to propagate? Only at the speed of sound. And then the load-to-bearing ratio simply gets worse with each column failure. There is no dramatic waiting around. Nature operates as fast as it can.
Can demolition crews time their charges to within milliseconds? The clue that you don't "get it," is your ridiculous assertion that a demolition crew would need to destroy only a few columns. As I have clearly explained, the net bearing strength of all columns taken together would have to be reduced to a safety factor of 1, and then all the columns would have to be severed. (Making reference to a failed demolition only says something about failed demolitions. Since there was no demolition, the reference is useless.)
I am an engineer with 3 degrees. In this exchange I have explained matters quantitatively. You have no refutation of this description of what happened, which conforms to the facts and is based on strict scientific principles of failure propagation. You bluster, denounce, deny, accuse, insult, and wish ill upon me. Not the best demonstration of a scientific or truth-seeking spirit.
No you’re not. You’re a glowing shill
I've seen this too many times. When the conversation gets to a point where the opponent cannot cope with the technical details or refute them, he resorts to name-calling and condemnation. I think you have outed yourself.
Things don’t collapse through the path of greatest resistance, retard glowie
When they don't have a choice, they do. The whole point of a structural collapse is the removal of resistance. An intact building had 1 g of resistance. The structural failure had 0.3 g of resistance. Where else was there to collapse? Spilling down outside of the walls of the lower building? Kind of impossible if the upper structural elements were still intact. Yeah, you tell me what the other path was. I'm waiting.