Which 7? the South side facing 1WTC had only 14 columns including the two corners?
At what floor were the 7 columns severed?
Total Building Collapse from a Single Column Failure
- Thread starter JSanderO
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Which 7? the South side facing 1WTC had only 14 columns including the two corners?
At what floor were the 7 columns severed?
Did you say you are an engineer and design multistory steel framed buildings?
Robrob
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Did you?
BasqueArch
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I believe he is. Few people know European building codes require structural design to prevent progressive collapse. Not that Official building plan reviewers here in the US can or could spot this. NIST tried this but was turned down by the IBC ... so far. IBC and ASCE-ACI however, have changed their codes to strengthen connections and expand fireproofing requiremts, as well as their bonding strength among other structural modifications directly related to the NIST 9/11 reports.
Did you say WTC7 slabs were not composite? If so, that's wrong. The forces acting were also dynamic not static, plus loss of floors = loss of columns bracing. Overall probable collapse sequence NIST got it right, fire FEA + lateral torsional bucking of the girder pushed it off floor 13. No smoke or fire was coming out of the diesel generator floors (louvered vented floor), and most of the diesel was recovered in the tanks during cleanup.
As long as I'm here, I was taught that slabs sat on Joists (multiples),Joists sat on Beams, Beams sat on Girders, regardless of their shapes. Why does NIST call WTC7 joists, "beams".
I believe he is. Few people know European building codes require structural design to prevent progressive collapse. Not that Official building plan reviewers here in the US can or could spot this. NIST tried this but was turned down by the IBC ... so far. IBC and ASCE-ACI however, have changed their codes to strengthen connections and expand fireproofing requiremts, as well as their bonding strength among other structural modifications directly related to the NIST 9/11 reports.
Did you say WTC7 slabs were not composite? If so, that's wrong. The forces acting were also dynamic not static, plus loss of floors = loss of columns bracing. Overall probable collapse sequence NIST got it right, fire FEA + lateral torsional bucking of the girder pushed it off floor 13. No smoke or fire was coming out of the diesel generator floors (louvered vented floor), and most of the diesel was recovered in the tanks during cleanup.
As long as I'm here, I was taught that slabs sat on Joists (multiples),Joists sat on Beams, Beams sat on Girders, regardless of their shapes. Why does NIST call WTC7 joists, "beams".
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MileHighMadness
Muse
When WTC 1 collapsed at 10:28:22 a.m., most of the debris landed in an area not much larger than the original WTC 1 building footprint. However, some fragments were forcibly ejected and travel distances up to hundred of meters. Pieces of WTC 1 hit WTC 7, severing six columns on Floors 7 through 17 on the south face and one column on the west face near the southwest corner. The debris also caused structural damage between Floor 44 and the roof.
The comments about the British Codes should more properly refer to their incorporation of the requirements of the Eurocodes but is substantially correct. Designers must make provision to prevent "dispropportionate collapse" in the event of the failure of one or more key elements.
This did, to a certain extent, exist in the older British Standards but the requirements were strengthened and expanded following analysis of the 911 collapse data.
I cannot speak about US design requirements based on any personal experience.
You appear to be assuming that a vertical element such a column only supports and transmits loads from a localised area immediately adjacent. This is only true in very simple structures and would not commonly be the case in complex multi-storey buildings.
By way of example, try cutting out the lower chord from a truss or girder, and see what happens.
Apples and oranges. A truss is a beam with the lower chord being the web.
The slabs were composite with the beams but regardless of what the EU standards for connections and so forth... if a single columns COLLAPSED and the EPH above it collapse right through the building, it was REMOVING the floor loads it fell upon as they all apparently landed in a pile on the ground. That is because the aggregate load of those bits of floor represented a load (force) which no floor would support.
The collapsing of the local floor area around column 79 likely did have an impact on the girders connected to the line of columns above the failed column 79. Those girders likely snapped at the connection to the columns surrounding the dropped 79 and or pulled those columns toward the collapsing line of col 79. This MAY be what explains the kink in the curtain wall and the moment frame of the north wall.
That kink means there were no longer floor plates/diaphragms attached to the moment frame and curtain wall. Flat plane with 40 slabs behind it can't bow or or out if the plates are still engaged with the flat plane (curtain wall w. moment frame)
Take away is there was no flooring on the north side of the core (at least) when the curtain wall drops.
What caused the columns around the perimeter base of the building to lose capacity and fail to support the perimeter moment frame which enabled those columns (perhaps) and curtain wall to descend at close to FF for 100" before slowing measurably. And can you tell us at what floor(s) this happened ?
erwinl
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Wouldn't those floors also affect the columns surrounding them as they fell down in this scenario?
Unless you use terminology differently in the US, I'm afraid that's not entirely accurate.
I'm sorry, but that's a gross oversimplification of structural mechanics in large complex structures. Whilst a column in a framed structure will principally carry directly imposed dead and dynamic loadings, it will typically also act as part of the wider structural system.
At the risk of a detailed technical discussion regarding finite state, plastic, and elastic terminology you will find that an individual structural element may well be assisting in (say) distributing the moment from imposed loads elsewhere, or bracing adjacent fabric. In short, it is the overall system which can be composite and hence failure of individual elements can lead to disproportionate collapse unless adequate redundancy is incorporated.
That is the whole point of the revisions to the Eurocodes and it involves a significant amount of structural design / cross-checking.
Can't say as I have a great interest in WT7 and someone else will doubtless answer such specific points of detail.
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Indeed the entire structure of a building... floor plates, columns, girders and beams act as a composite. This is not in dispute. But complexity may be.
The frame is typically, and in the case of 7WTC bolted together, with the floor plates having shear studs making them composite with the beams and girders.
Yes there is ALWAYS an element of over design. It's included in the tables for steel sections.
Eurocodes have nothing to do with 7WTC which was designed and erected decades before this was addressed in Europe. It's irrelevant to this discussion.
If a column is removed the axial loads upon it and the floor loads attached to it can no longer use the failed column to transmit load to bedrock.
The loads must be supported by the remaining frame/structure or drop... which is what happened to the area under the EPH. Failure of column 79 was below the EPH failed... perhaps even caused by the collapse of TT1 (my hunch) and all the columns above the failed one AND the floor areas attached to it came down. EPH can't pass magically through the floors. It was the top of a 40+ story local floor collapse which included the columns under it. PERIOD.
Now aside from claiming complexity... if the loads of the EPH and every floor below it were removed because the fell to the ground... WHAT LOADS are redistributed?
As I wrote... you can assert that the collapsing floors around col 79, 80 and 81 pulled at the columns around them but you can state that the loads were redistributed. And there is SOME evidence of this pull which was the full ht kink in the north facade.
But the only mechanism to account for collapse of the WPH is some sort of pull of the frame by the collapse of the beams and girders from the collapse of col 70,80 and 81. This suggests that the pull caused floor areas to collapse as far west as the WPH at least on the north side of the core.
But it does not explain how the support for the perimeter columns under the curtain was were compromised.
I suppose you are unaware that TT3 was a cantilever truss with the column on the end of the cantilever under the WPH. Possible connection to look at?
I think so.
chrismohr
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Several people seem to be wondering what JSanderO is getting at. Are you worried he may be proposing CD as the cause of the collapses? JSanderO can explain this much better than me, but I believe he is "getting at" his sinkhole hypothesis, which is that instead of Column 79 triggering a series of cascading column failures, when one column fails the internal structure around it collapses towards the ground instead of quickly shifting the load to nearby columns. JSanderO, does that at least kind of explain "what you're getting at"?
jaydeehess
Penultimate Amazing
Have not read the entire thread, not enough time as yet. However it should be noted that WTC 7 was a very complex structure, from foundation to 8th floor especially.
I said in the other thread that I believe that its quite possible that the single failure of col 79 led to debris damage to TT1 that then caused further failures including that of col 80 & 81.
Load redistribution was not the primary cause of failure progression, imho. It was debris impacts that caused caused the first progressions beyond col 79.
col 79 fails, debris is raining down on TT1. col 80 is pulling in as col 79 fails AND col 80's base at TT1 is under attack by debris. Col 80 fails at TT1, TT1 fails under increasing debris falls, col 81 falls with TT1, TT1failure means the eastern extent of the western core has also failed compromising TT2 TT3 and the lateral support of the core columns under the cantilever trusses.
The girder walk off itself was aided by the design of the structure that had no symmetric beam placements to counter the movement of the girder, as would have been the case in a more classic post and beam structure.
I feel that question was a bit of hyperbole on the part of Mr.JSO
I said in the other thread that I believe that its quite possible that the single failure of col 79 led to debris damage to TT1 that then caused further failures including that of col 80 & 81.
Load redistribution was not the primary cause of failure progression, imho. It was debris impacts that caused caused the first progressions beyond col 79.
col 79 fails, debris is raining down on TT1. col 80 is pulling in as col 79 fails AND col 80's base at TT1 is under attack by debris. Col 80 fails at TT1, TT1 fails under increasing debris falls, col 81 falls with TT1, TT1failure means the eastern extent of the western core has also failed compromising TT2 TT3 and the lateral support of the core columns under the cantilever trusses.
The girder walk off itself was aided by the design of the structure that had no symmetric beam placements to counter the movement of the girder, as would have been the case in a more classic post and beam structure.
So, does this single point of failure in 7WTC mean potential disaster for all other steel framed buildings, no , of course not.
I feel that question was a bit of hyperbole on the part of Mr.JSO
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jaydeehess
Penultimate Amazing
Neither, imho, would the failure of columns above the Con-Ed structure , other than, possibly, those at either end of a cantilever truss.
Obviously the destruction of the NW corner column would not lead to total collapse either as that was 'tested' on 9/11.
One would have to look at how a col failure directly under a heavy dense component such as an A/C unit or elevator motor would affect the structure. Such a heavy chunk of debris may well be able to smash through several floors after falling 3 meters.
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jaydeehess
Penultimate Amazing
No, he is just pushing his own take on the cause of collapse.
CTBUH had their own questions regarding the walk off of the girder, they wondered about the cooling, contraction phase as a cause rather than heating expansion.
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Chris,
This is basically what I am proposing... there were two processes going on... collapse of floors disengaging from columns... and some pulled of the frame in certain locations.
My theory is that column 79 failure was NOT the initial failure but TT#1 which cause 79 to drop alone with the floors around it... AND pulled the girder running north attached to the core columns which yanked TT#3 and dislodged the 8 MG17 girders which supported the columns of the north curtain wall opposite the core on cantilevers.
Problem for your analysis is that it does not match the movements. TT#1 failed BEFORE column 79... 79 did NOT destroy TT1 as it was not under it.
You got the sequence backwards but yes the complexity below 8 likely caused the floors etc north of the core to collapse pull the braced wind frames below 8 in and that allowed the curtain wall to drop.
Yes I am suggesting a different sequence of failures which originated in the load transfer structures probably TT#1.
I feel it's a better fit than the column 79 single column initiation. You betcha.