Correct speed of building collapse

[swskeptic]

I know the buildings didn't collapse at free fall.

My problem is, what would the correct speed be?

The 13.48 and 12.07 second times found by (Dr. Greening). I know he also says these are the minimum. I'm also aware of the large chunk of the center columns left standing after the initial collapse.

Anyways though, back to my original question, what should the times be? 13.48 seconds? 20 seconds? 30 seconds? Is there no scientific way to accurately calculate this?

 

[Totovader]

When I timed the collapses myself based on the best vantage points- I came up with at least 18 seconds...



I erred on the side of caution- I probably could have started the timers a lot sooner, but I was simply trying to address the "free fall" claim, and didn't find it necessary to be precise.

 

[Alferd_Packer]

The concept of a "correct" speed begs the question that there is an "incorrect" speed.

 

[rcronk]

I remember Leslie Robertson (WTC structural engineer) saying in a "debate" with Steven Jones that they fell at the speed at which he expected them to fall as any individual floor basically would not slow down the collapse much since the floors weren't designed to hold multiple floors worth of building falling on them.

I think a decent structural engineer might be able to get some kind of estimate put together (maybe one has already) but to get an exact value, you'd have to build a perfect computer model or build an identical WTC and perfectly reproduce 9/11, both of which are impossible.

Another hurdle you'd have to overcome is that I can't see a real reason to calculate such a number. Even if you could calculate it, what would you use that number for? To convince a truther of something? No - they'd dismiss the number if it didn't fit their theory, so you would have wasted a lot of time and effort to come up with a useless number IMO. There's enough evidence out there that makes such a number basically unnecessary - especially since there's a large margin of error on measuring the collapse so if the engineer (not Judy Wood ) came up with 12 seconds, the truthers would just quote anyone who said they timed it as any number less than 12 and use that as more truther ammo. Well, that's my 2¢ anyway.

 

[The Big Dog]

I am still amazed this free fall thing gets any traction. There is a well known video (it is a hand held video on the street near the towers, part of which has film of an injured pedestrian, I'll dig it up somehow) in which the first tower can be seen collapasing before the camera man takes off running. Right before he takes off, you can see actual "freefall" of part of the tower: namely a huge chunk of the facade that peeled off and fell down the side of the tower hitting the ground. Next you see some other free fall objects that were ejected, and then he runs. Point being: Debris is seen falling faster than the collapse front is moving; therefore the building cannot be collapsing at free-fall speed.

 

[jhunter1163]

It's obviously very difficult to say with certainty just when the collapses ended, due to the large amount of obscuring dust. Most sources, though, are in the range of 12-15 seconds. This agrees well with calculations as well as the seismographic data.

FWIW, when confronted with this argument I make two points:

1) Debris is seen falling faster than the collapse front is moving; therefore the building cannot be collapsing at free-fall speed.

2) No matter what Judy Wood and Sofia Shafquat say, the building would be expected to collapse at about the rate it did (10-20% slower than free fall). There simply wasn't enough strength in the lower portion of the Tower to slow the collapse significantly.

ETA: Ah, beaten to it. Repeatedly. I have to step up my game.

 

[tsig]

I know the buildings didn't collapse at free fall.

My problem is, what would the correct speed be?

The 13.48 and 12.07 second times found by (Dr. Greening). I know he also says these are the minimum. I'm also aware of the large chunk of the center columns left standing after the initial collapse.

Anyways though, back to my original question, what should the times be? 13.48 seconds? 20 seconds? 30 seconds? Is there no scientific way to accurately calculate this?

Yes what should the times be? Does everyone have to hold your hand and do your work for you? We would spoon feed you but we've seen too many gag. Cleaning up after is the pits.

 

[rcronk]

When I timed the collapses myself based on the best vantage points- I came up with at least 18 seconds...



I erred on the side of caution- I probably could have started the timers a lot sooner, but I was simply trying to address the "free fall" claim, and didn't find it necessary to be precise.

Eeek. It's shocking to hear truther drivel (from your video clip of the truther) from someone's face instead of just reading it in a forum thread. It's just so disturbing.

 

[mortimer]

I am still amazed this free fall thing gets any traction. There is a well known video (it is a hand held video on the street near the towers, part of which has film of an injured pedestrian, I'll dig it up somehow) in which the first tower can be seen collapasing before the camera man takes off running. Right before he takes off, you can see actual "freefall" of part of the tower: namely a huge chunk of the facade that peeled off and fell down the side of the tower hitting the ground. Next you see some other free fall objects that were ejected, and then he runs. Point being: Debris is seen falling faster than the collapse front is moving; therefore the building cannot be collapsing at free-fall speed.

You're just not thinking truthfully enough. Obviously, explosives were used to accelerate debris downward, making it appear that the building wasn't falling at free-fall speed, which the explosives did cause to happen. Duh.

 

[gumboot]

I am still amazed this free fall thing gets any traction. There is a well known video (it is a hand held video on the street near the towers, part of which has film of an injured pedestrian, I'll dig it up somehow) in which the first tower can be seen collapasing before the camera man takes off running. Right before he takes off, you can see actual "freefall" of part of the tower: namely a huge chunk of the facade that peeled off and fell down the side of the tower hitting the ground. Next you see some other free fall objects that were ejected, and then he runs. Point being: Debris is seen falling faster than the collapse front is moving; therefore the building cannot be collapsing at free-fall speed.

It's a pity that cameraman wasn't using High Definition, or a more powerful zoom lens, otherwise he no doubt would have picked up the tiny rockets attached to the debris which were propelling it earthwards faster than the free-fall collapse wave.

 

[GregoryUrich]

I know the buildings didn't collapse at free fall.

My problem is, what would the correct speed be?

The 13.48 and 12.07 second times found by (Dr. Greening). I know he also says these are the minimum. I'm also aware of the large chunk of the center columns left standing after the initial collapse.

Anyways though, back to my original question, what should the times be? 13.48 seconds? 20 seconds? 30 seconds? Is there no scientific way to accurately calculate this?

Bazant, Le, Greening and Benson give an interpretation of the Seismic data as indicating 12.58 +/- 0.5 and 10.09 +/- 0.5 seconds for the North and South towers respectively.

NIST says (in their FAQ):

NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: (1) precise timing of the initiation of collapse from video evidence, and (2) ground motion (seismic) signals recorded at Palisades, N.Y., that also were precisely time-calibrated for wave transmission times from lower Manhattan (see NCSTAR 1-5A).
...
From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.

So NIST says essentially, "we don't know".

Now, if the acceleration was constant, it would be possible to extrapolate from the video portions where the top is visible. I think Benson (mentioned above) and Einsteen have worked somewhat on this.

There are many theoretical calculations of the expected collapse times usually measuring the time from collapse initiation (visible movement) to impact of the collapse front with the bedrock, or sometimes ground level. Most have focused on the North tower because it is a less severe case in terms of the potential survival of the structure. The results of these calculations usually range from 12-25 seconds. Some have the collapse arresting. All the calculations I have seen are too simplified to give reliable results.

Many people arguing against controlled demolition like to argue that since portions of the core were standing the building wasn't collapsed yet. Technically this is correct, but this has no bearing on the point in time at which the collapse front hits the bedrock which could be compared to a calculated expected collapse time.

In order to do more realistic calculations of the collapse times the following must be established:

1. failure mode - floor by floor column buckling is usually used, but there is little evidence supporting it
2. column elastic strain energy - the spring(s) stiffness C is not generally agreed upon
3. floor elastic strain energy - some energy is absorbed by flexion of the floor diaphrams
4. energy due to inelastic collision - this is pretty well known and accepted
5. floor plastic strain energy - often referred to as comminution of concrete. Newtons Bit denies this is a factor due to the ineastic collision, but the collision is not purely inelastic. In fact the upper floor of the lower part is restrained for some period of time at each impact.
6. column plastic strain energy - we don't have a generally agreed upon value for this at the first impact
7. scaling of column plastic strain energy - most models don't use this but it should be added
8. column plastic energy during the initial collapse - most models do not include this
9. elastic and plastic strain energies for floors and horizontal members - most models do not include this
10. sheading of mass - there is no real agreement on the amount of mass expelled. It probably ramps up to a maximum at the first mechanical floors reached by the collapse front.

There are more issues, but this would be a start.

 

[stateofgrace]

In order to do more realistic calculations of the collapse times the following must be established:

1. failure mode - floor by floor column buckling is usually used, but there is little evidence supporting it
2. column elastic strain energy - the spring(s) stiffness C is not generally agreed upon
3. floor elastic strain energy - some energy is absorbed by flexion of the floor diaphrams
4. energy due to inelastic collision - this is pretty well known and accepted
5. floor plastic strain energy - often referred to as comminution of concrete. Newtons Bit denies this is a factor due to the ineastic collision, but the collision is not purely inelastic. In fact the upper floor of the lower part is restrained for some period of time at each impact.
6. column plastic strain energy - we don't have a generally agreed upon value for this at the first impact
7. scaling of column plastic strain energy - most models don't use this but it should be added
8. column plastic energy during the initial collapse - most models do not include this
9. elastic and plastic strain energies for floors and horizontal members - most models do not include this
10. sheading of mass - there is no real agreement on the amount of mass expelled. It probably ramps up to a maximum at the first mechanical floors reached by the collapse front.

There are more issues, but this would be a start.

You have had six years to "start" this, what are you waiting for?

Get to it and give us your calculated time.

 

[Furcifer]

Is there no scientific way to accurately calculate this?

Nope. There's too many variables to account for in a chaotic system to arrive at an accurate calculation of the collapse time.

 

[GregoryUrich]

You have had six years to "start" this, what are you waiting for?

Get to it and give us your calculated time.

Easy bud, I've only been on the case for a year and put in about 400 hrs on the mass analysis which has direct bearing on this. Right now I'm focused on the Bazant "Simple Analysis" which may give answers to some of the above issues. With my current best guesses I get 21 seconds, but I'm not going to jump up and down and yell "controlled demolition" because there are too many things that are unknown and I'm not even sure if a 1-d analysis can prove anything.

By the way, what's your contribution other than heckling from the sidelines?

 

[beachnut]

Bazant, Le, Greening and Benson give an interpretation of the Seismic data as indicating 12.58 +/- 0.5 and 10.09 +/- 0.5 seconds for the North and South towers respectively.

NIST says (in their FAQ):
So NIST says essentially, "we don't know".

Now, if the acceleration was constant, it would be possible to extrapolate from the video portions where the top is visible. I think Benson (mentioned above) and Einsteen have worked somewhat on this.

There are many theoretical calculations of the expected collapse times usually measuring the time from collapse initiation (visible movement) to impact of the collapse front with the bedrock, or sometimes ground level. Most have focused on the North tower because it is a less severe case in terms of the potential survival of the structure. The results of these calculations usually range from 12-25 seconds. Some have the collapse arresting. All the calculations I have seen are too simplified to give reliable results.

Many people arguing against controlled demolition like to argue that since portions of the core were standing the building wasn't collapsed yet. Technically this is correct, but this has no bearing on the point in time at which the collapse front hits the bedrock which could be compared to a calculated expected collapse time.

In order to do more realistic calculations of the collapse times the following must be established:

1. failure mode - floor by floor column buckling is usually used, but there is little evidence supporting it
2. column elastic strain energy - the spring(s) stiffness C is not generally agreed upon
3. floor elastic strain energy - some energy is absorbed by flexion of the floor diaphrams
4. energy due to inelastic collision - this is pretty well known and accepted
5. floor plastic strain energy - often referred to as comminution of concrete. Newtons Bit denies this is a factor due to the ineastic collision, but the collision is not purely inelastic. In fact the upper floor of the lower part is restrained for some period of time at each impact.
6. column plastic strain energy - we don't have a generally agreed upon value for this at the first impact
7. scaling of column plastic strain energy - most models don't use this but it should be added
8. column plastic energy during the initial collapse - most models do not include this
9. elastic and plastic strain energies for floors and horizontal members - most models do not include this
10. sheading of mass - there is no real agreement on the amount of mass expelled. It probably ramps up to a maximum at the first mechanical floors reached by the collapse front.

There are more issues, but this would be a start.

You can skip this guy and use the video of 9/11, the buildings falling. That is what the WTC does when it fails to hold a section above that weighs more than a floor can hold. The video shows how the WTC looks, and how fast it falls; you can skip calculations, you can use the real MODEL.

WARNING<>This post is from someone, who without facts, has signed up to be a 9/11 truth member. He is a pure truther who will not admit it, but has signed the petition of woo (he blames many who did not do it, but fails to present evidence)

Signatory of Petition of Solidarity to the Attorney General of New York for a new independent grand jury investigation of 9/11 11/19/04: "We the undersigned: a) think that there is ample evidence and probable cause to believe that many grave and still unresolved crimes were committed by US officials prior to, during and after the events of 9/11; b) observe that most of these apparent crimes, including but not limited to abetment of mass murder, criminal negligence, insider trading, and obstruction of justice fall well within the jurisdiction of New York's top law enforcement officials ..." http://www.justicefor911.org.

You can model all you want, I think the best indication of speed of collapse is seen on 9/11. No bombs, no thermite, just gravity after the terrorist used planes to cut the fire systems with impacts equal in energy to 1300 to 2200 pounds of TNT; into a building that was design to with stand only 187 pounds of TNT impact from a plane!

If you must do a simple model a good start is the ironic Dr Greening, and his work. You can model the strength of each floor on your own and come up with a 10 to 20 percent increase in collapse time vs. free fall from ~1300 feet. That is a second or two! One of the keys for failure is the WTC floors can only hold so much weight. On 9/11 more than 10 floors failed and the floors below could not handle the increased weight. Most of the "9/11 truth engineers try to model the WTC towers as a set strength based on column strength, and fail to model a single floor failure. It is obvious the WTC can hold up much more than itself, but a single floor will fail with only 11 additions floors of weight, not counting the extra structure of the shell, or core falling also. This single point failure also affects the entire building, as a floor fails there is no longer support for the shell, or the core. The core does not handle lateral loads, and without the floors to tie the core to the shell, the structure is doomed. There is no quick understanding of the WTC failure, but the way, and the time it fell is documented on 9/11 in video. NIST did not do a study mainly to show you can happen, they had to verify the building was as strong as it was suppose to be. As you can see this post by Greg is biased to his belief we did 9/11 to ourselves and UBL is a kind and gentle man. His basis for all the silly model requirements is to try and prove the WTC can not fail due to impact and fire. He does not care if he has to manufacture false information, or post lies from others to cast doubt the WTC failed due to the terrorist action alone. He is blaming others for the actions UBL alone takes credit for. To be less than honorable is the way of 9/11 truth.

The reason people have a hard time understanding the failure is the massive amount of energy released due to gravity.

To get a good feel for the collapse mechanism of the WTC, you must study NIST, and all the other papers you can. It is not as simple as impact, fire, and collapse; BUT it is.

You get back to the full scale model, the real WTC, failed as we saw it on 9/11.

 

[GregoryUrich]

Nope. There's too many variables to account for in a chaotic system to arrive at an accurate calculation of the collapse time.

So, BLGB is not reliable?

 

[Walter Ego]

I am still amazed this free fall thing gets any traction. There is a well known video (it is a hand held video on the street near the towers, part of which has film of an injured pedestrian, I'll dig it up somehow) in which the first tower can be seen collapasing before the camera man takes off running. Right before he takes off, you can see actual "freefall" of part of the tower: namely a huge chunk of the facade that peeled off and fell down the side of the tower hitting the ground. Next you see some other free fall objects that were ejected, and then he runs. Point being: Debris is seen falling faster than the collapse front is moving; therefore the building cannot be collapsing at free-fall speed.

In almost every video I've seen the debris is falling faster than the towers.

 

[beachnut]

Nope. There's too many variables to account for in a chaotic system to arrive at an accurate calculation of the collapse time.

Greg may not understand your post, but, his current avatar, perfect avatar for 9/11 truth's expertise on issues.

His old avatar indicative of 9/11 truth to see facts, inversely proportional to 9/11 truth skills.

I think you are right! I am sticking with the failure times as seen on the collapse videos filmed on 9/11 on the full scale model. I hate simple models and the WTC is unique, all of the attempts by truthers have failed to even model how the WTC collapsed or did not collapse as they try to back in CD/thermite/beam weapons/dustification/RDX/thermate/other stupid ideas.

 

[Furcifer]

So, BLGB is not reliable?

Nope. At least for purposes of being "scientifically accurate". I would say it is at present "our best scientific approximation". But nothing more.

So then we turn to collapse initiation. Again, out best attempts are befuddled by the staggering number of variables and the chaotic nature of the system.

I didn't pick this username on a whim Greg

 

[KDLarsen]

This thread wouldn't be complete without at least one reply mentioning the clunkety-clunk theory