13-09-2012, 02:34 AM
(This post was last modified: 13-09-2012, 03:14 AM by Jeffrey Orling.)
Lauren,
Since you asked.... I hadn't examined bldg 7 very much until about 1 yr ago. I focused on the twin towers which I understand quite well structurally.
The NIST explanation of the failure of shear studs from the heating of the girder which then moved off the beam seat on column 79 was pure hooey and did not lead to the collapse. And I don't even think it "walked off" the beam seat either. That was a completely theoretical, not evidence based theory.
The truth movement used the following evidence to conclude CD:
2.25 seconds of free fall collapse
The building came stright down
explosion(s) were heard at some point
eutectic burning of some steel members was seen
These are very peculiar, but none of them is proof of the CD conclusion. CD may produce those observables..
But other causes can produce them as well.
When I examined the structure more closely AND the observables I determined that the building collapsed from a structural failure on floors 6&7. Why?
Bldg 7 was a real odd duck of a hi rise steel tower. Unlike any other ever built! It was unique! Why?
It was built to straddle a massive Con Ed power station which occupied most of the site where the tower was to be built. So the tower... was built on a structure which spanned over the sub station. This meant that many of the columns which carried the building's weight were not resting on bed rock. What were they resting on? Massive trusses or at the ends of cantilevers. The tower was missing lots of columns below the 8th floor and so the many of the 81 columns of the towers were supported by massive 2 story high trusses. It was like a bridge over the sub station. And two of the walls...east and west up to those trusses were also trusses and not columns. You can think of the structure like a huge auditorium or concert hall with a skyscaper built on the roof. If the roof collapses.. the skyscaper above plunges down through the 8 story high auditorium to the ground... and the auditoriun walls folded in as the tower collapses down. Not a perfect analogy... but it might help to understand why it collapsed straight down into its foot print.
So what might have failed the structure on floors 6&7 - the trusses and cantilever girders?
To fail a truss... one doesn't have to destroy every member. Remember the truss bridge which collapsed into the Mississippi river in MN?
http://www.ce.berkeley.edu/~astaneh/I-35...-Final.pdf
If one member fails... its failure can lead to the failure (rapidly) of the whole truss. In the case of bldg 7 it one of the trusses failed it no longer could carry the loads from the columns which rested on it. Those columns might drop... and the east penthouse was above Transfer Truss 3 and did drop down through the entire building BEFORE the rest of the building dropped.
The loads of TTruss 3 would then be re distributed to adjacent structures. These columns or trusses COULD support additional loads. They DID have a safety factor. It was about 1.5. So they could carry 50% extra load. But if the saw MORE than an additional 50% they too would collapse and then the columns adjacent to it would see BOTH additional loads and so on. The failure can progress VERY rapidly and usually does. The failure cascades through the system.
https://en.wikipedia.org/wiki/Cascading_failure
How could this have happened?
Bomb some of the truss members
Weaken them with heat
Steel loses strength when subjected to heat. That's why it is fire proofed and why there are sprinklers.
The trusses were not protected by fire proofing nor sprinklers I believe and the water main broke and the power went down shortly after tower 1 was hit.
There were many huge transformers cooled with flammable oil located in the sub station and on floor 5. Jennings and Hess reported explosions below them when they were in the stair going down BEFORE 10 am. This came from the mech floors where the electrical power equipment was located including the emergency generators fueled by stored diesel.
The building's structural engineer believed the trusses failed from diesel fueled flames.. unfought for 7 hrs. The entire truss did not have to melt or even weaken.. only one member and the truss would give way.
The NYC DOB and FDNY surveyed the building... likely the mech floors where the fire was heating the trusses etc and determined that the building and area needed to be evacuated as it might collapse. They of course reported this to the media.. and Jane Staley did a BBC stand up stating that the building HAD collapsed. There was fore knowledge that the tower was in trouble. Evacuating the area when a collapse may occur is SOP.
When the structure on 6&7 gave way the top dropped 100 feet to the ground at FF. There was little below this structure to slow it down.
The north facade showed inward bowing as if there was nothing behind it. This was the region where the 8 columns just inside the facade were supported on cantilevers.
The entire building swayed east and west a few feet (IIRC) before there was any obvious movement then the east penthouse plunged to the ground over t truss 3 and the the west penthouse came down...both were over the core region which was supported by the 3 trusses. It looks like the trusses failed.
What failed the trusses?
If you don't closely examine the structure... you can't understand what happened to it.
Since you asked.... I hadn't examined bldg 7 very much until about 1 yr ago. I focused on the twin towers which I understand quite well structurally.
The NIST explanation of the failure of shear studs from the heating of the girder which then moved off the beam seat on column 79 was pure hooey and did not lead to the collapse. And I don't even think it "walked off" the beam seat either. That was a completely theoretical, not evidence based theory.
The truth movement used the following evidence to conclude CD:
2.25 seconds of free fall collapse
The building came stright down
explosion(s) were heard at some point
eutectic burning of some steel members was seen
These are very peculiar, but none of them is proof of the CD conclusion. CD may produce those observables..
But other causes can produce them as well.
When I examined the structure more closely AND the observables I determined that the building collapsed from a structural failure on floors 6&7. Why?
Bldg 7 was a real odd duck of a hi rise steel tower. Unlike any other ever built! It was unique! Why?
It was built to straddle a massive Con Ed power station which occupied most of the site where the tower was to be built. So the tower... was built on a structure which spanned over the sub station. This meant that many of the columns which carried the building's weight were not resting on bed rock. What were they resting on? Massive trusses or at the ends of cantilevers. The tower was missing lots of columns below the 8th floor and so the many of the 81 columns of the towers were supported by massive 2 story high trusses. It was like a bridge over the sub station. And two of the walls...east and west up to those trusses were also trusses and not columns. You can think of the structure like a huge auditorium or concert hall with a skyscaper built on the roof. If the roof collapses.. the skyscaper above plunges down through the 8 story high auditorium to the ground... and the auditoriun walls folded in as the tower collapses down. Not a perfect analogy... but it might help to understand why it collapsed straight down into its foot print.
So what might have failed the structure on floors 6&7 - the trusses and cantilever girders?
To fail a truss... one doesn't have to destroy every member. Remember the truss bridge which collapsed into the Mississippi river in MN?
http://www.ce.berkeley.edu/~astaneh/I-35...-Final.pdf
If one member fails... its failure can lead to the failure (rapidly) of the whole truss. In the case of bldg 7 it one of the trusses failed it no longer could carry the loads from the columns which rested on it. Those columns might drop... and the east penthouse was above Transfer Truss 3 and did drop down through the entire building BEFORE the rest of the building dropped.
The loads of TTruss 3 would then be re distributed to adjacent structures. These columns or trusses COULD support additional loads. They DID have a safety factor. It was about 1.5. So they could carry 50% extra load. But if the saw MORE than an additional 50% they too would collapse and then the columns adjacent to it would see BOTH additional loads and so on. The failure can progress VERY rapidly and usually does. The failure cascades through the system.
https://en.wikipedia.org/wiki/Cascading_failure
How could this have happened?
Bomb some of the truss members
Weaken them with heat
Steel loses strength when subjected to heat. That's why it is fire proofed and why there are sprinklers.
The trusses were not protected by fire proofing nor sprinklers I believe and the water main broke and the power went down shortly after tower 1 was hit.
There were many huge transformers cooled with flammable oil located in the sub station and on floor 5. Jennings and Hess reported explosions below them when they were in the stair going down BEFORE 10 am. This came from the mech floors where the electrical power equipment was located including the emergency generators fueled by stored diesel.
The building's structural engineer believed the trusses failed from diesel fueled flames.. unfought for 7 hrs. The entire truss did not have to melt or even weaken.. only one member and the truss would give way.
The NYC DOB and FDNY surveyed the building... likely the mech floors where the fire was heating the trusses etc and determined that the building and area needed to be evacuated as it might collapse. They of course reported this to the media.. and Jane Staley did a BBC stand up stating that the building HAD collapsed. There was fore knowledge that the tower was in trouble. Evacuating the area when a collapse may occur is SOP.
When the structure on 6&7 gave way the top dropped 100 feet to the ground at FF. There was little below this structure to slow it down.
The north facade showed inward bowing as if there was nothing behind it. This was the region where the 8 columns just inside the facade were supported on cantilevers.
The entire building swayed east and west a few feet (IIRC) before there was any obvious movement then the east penthouse plunged to the ground over t truss 3 and the the west penthouse came down...both were over the core region which was supported by the 3 trusses. It looks like the trusses failed.
What failed the trusses?
If you don't closely examine the structure... you can't understand what happened to it.