DGM
Skeptic not Atheist
This is the theory in earthquakes also. Let the building shake around and twist, it may be a total loss but, it's likely better for the occupants.
OOS Collapse Propagation Model
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For the same reason a race car body has to crumple and tear away. To absorb energy without inflicting damage to structural parts. You're safer in a 2015 Toyota into a tree then a '57' Buick for the same reason.
The facade was more than 50% of the "structure"... right? So with the columns very closely spaced... 20" apart.... wouldn't a plane hitting do more damage to the WTC than if there were columns at 30' OC?
How many columns would a plane destroy in a 30x30' grid?
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If only a portion of a building is damaged... why wouldn't it collapse down to grade and ALSO take the rest of the structure with it? What did Mr B say about one section say... a corner outside the core collapsing... would that destroy the entire tower? How does that work?
There is more than shaking because ground can heave and create moments and and cause toppling. They say:
Low Height to Base Ratios
Equal Floor Heights
Symmetrical Plans
Uniform Sections and Elevations
Maximum Torsional Resistance
Short Spans and Redundancy
Direct Load Paths
and
Hysteric dampers utilize the deformation of metal parts
Visco-elastic dampers stretch an elastomer in combination with metal parts
Frictive dampers use metal or other surfaces in friction
Viscous dampers compress a fluid in a piston-like device
Hybrid dampers utilize the combination of elastomeric and metal or other parts
and
Where is the location of the nearest fault?
Are there unconsolidated natural or man-made fills present?
Is there a potential for landslide or liquefaction on or near the site?
Are there vulnerable transportation, communication, and utilities connections?
Are there any hazardous materials on the site to be protected?
Is there potential for battering by adjacent buildings?
Is there exposure to potential flood from tsunami, seiche, or dam failure?
Conform to local building codes providing "Life Safety," meaning that the building may collapse eventually but not during the earthquake.
Design for repairable structural damage, required evacuation of the building, and acceptable loss of business for stipulated number of days.
Design for repairable nonstructural damage, partial or full evacuation, and acceptable loss of business for stipulated number of days due to repair.
Design for repairable structural damage, no evacuation required, and acceptable loss of business for stipulated number of days due to repair.
No structural damage, repairable nonstructural damage, no evacuation, and acceptable loss of business for stipulated number of days due to repair.
No structural or nonstructural damage, and no loss of business caused by either (excluding damage to tenants' own equipment such as file cabinets, bookshelves, furniture, office equipment etc. if not properly anchored).
Seismic design objectives can greatly influence the selection of the most appropriate structural system and related building systems for the project. Some construction type options, and corresponding seismic properties, are:
Wood or timber frame (good energy absorption, light weight, framing connections are critical).
Reinforced masonry walls (good energy absorption if walls and floors are well integrated; proportion of spandrels and piers are critical to avoid cracking)
Reinforced concrete walls (good energy absorption if walls and floors well integrated; proportion of spandrels and piers are critical to avoid cracking)
Steel frame with masonry fill-in walls (good energy absorption if bay sizes are small and building plan is uniform)
Steel frame, braced (extensive bracing, detailing, and proportions are important)
Steel frame, moment-resisting (good energy absorption, connections are critical)
Steel frame, eccentrically braced (excellent energy absorption, connections are critical)
Pre-cast concrete frame (poor performer without special energy absorbing connections)
What was the seismic strategy of the twin towers?
DGM
Skeptic not Atheist
I don't know, do you? Purdue says the NIST far under estimated the damage the planes did to the towers. They claim the fuel mass alone was never acounted for in structural damage.
You're starting your baseline from nothing and claiming the building didn't perform well. I wonder how Major Tom verifies the actual damage inflicted by the aircraft?
Wouldn't that be the state you would need to analyze a buildings potential for collapse? Surely as built or some estimate of damage wouldn't do. Could you point me to his page were he documents this information?
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DGM
Skeptic not Atheist
I find it telling you spent this much time on a minor comparison. You're "truther" is hanging out.
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Tony Szamboti
Illuminator
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Which part of the wings? Are the engines part of the wing?
Who was flying the aircraft in your realcddeal fantasy version of 911?
Why did the oops model fail to cure your CD fantasy?
How does the missing jolt support or not support the oops model?
ozeco41
Philosopher
Certainly none above the impact zone. If the design was not able to flex and respond to the impact it could have collapsed immediately. Maybe not total but, it makes you appreciate the fact the WTC design flexed and did not collapse right away.
Please take care - all of you - that you don't build false implications out of partial truths.
@DGM "If the design was not able to flex and respond to the impact it could have collapsed immediately." flexure is a reality in any structure. Your conditional could makes the first assertion a truism. But the causal relationship "flexure" >> "not collapse" is not necessarily true. Possibly isn't true but is definitely unproven at this stage.
AND
"...the WTC design flexed" and "did not collapse right away" is the true sequence but the two issues are not directly causally related. We cannot say "the Twins did not collapse immediately because they were flexible". You may not be intending that implication but is is there - so Sander has queried the implication and it looks like Bravin has accepted it. I may be wrong on that point.
It may be that WTC design had more flexibility which helped it more than other designs but the causality is not proven at this stage. @Sander "why does it have to flex?" That is a valid question whether you realised the engineering justification or not. All structures will flex but any implication that flexure of WTC was "different' and somehow protected it "better" is unproven. So I am cautioning - disregard the implication of proven causality. The question is much more subtle.
Your other points - as usual are valid issues for exploring - but they are derails at this stage. You go close to stating the actual true situation. "If more damage had been done the collapse would have been immediate or not delayed as long".
@Bravin Neff Your conclusion "...allowed hundreds if not thousands of people to survive" is perfectly correct IMO - but it was "the design of the WTC Twins" which allowed allowed those escapes - the relevance and causal linking of "flexibility" to "delay" is not secure. Accepting or implying causality is making the error that I've cautioned DGM and Sander about. This "could reasonably argue the flexing and not-collapsing-right-away feature" It is not one "feature" two separate issues - yes some overlap - but the presumption that they are directly linked as "one feature" is not secure.
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Do you?
ftp://ftp.ecn.purdue.edu/ayhan/Korucu/Karim and Fatt_(ASCE)0733-9399(2005)131_10(1066).pdf
Which part of the wing?
Crazy Chainsaw
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Please take care - all of you - that you don't build false implications out of partial truths.
@DGM "If the design was not able to flex and respond to the impact it could have collapsed immediately." flexure is a reality in any structure. Your conditional could makes the first assertion a truism. But the causal relationship "flexure" >> "not collapse" is not necessarily true. Possibly isn't true but is definitely unproven at this stage.
AND
"...the WTC design flexed" and "did not collapse right away" is the true sequence but the two issues are not directly causally related. We cannot say "the Twins did not collapse immediately because they were flexible". You may not be intending that implication but is is there - so Sander has queried the implication and it looks like Bravin has accepted it. I may be wrong on that point.
Sorry Ozeco41, your wrong and that is shown in the seismic data, the towers were highly
Efficient at absorbing and redirecting the impacts energy.
This was because of the flexibility of the design, that was built in to help with wind loading
that is why Rodertson said the towers could dissipate the impact of a 707. They were designed to flex. Your talking about a purposely designed feature of the buildings, if the perimeter columns had been welded instead of bolted, the towers could not have absorbed
the energy as well.
So how did Robertson design the building to take a 707 strike at x miles per hr? Does anyone here know what he did to make it "strong enough" to not????? fall down immediately on impact?
What would the difference be had he simply ignored a plane strike? Was this the same sort of design for wind shear?
Does flex mean that the joints have some "give" like an expansion joint in a bridge span?
We have heard many times that the towers were remarkably strong and were designed to take a plane strike... multiple ones one person stated and remain standing.
My sense is that the facade was like a huge membrane... that WAS a design innovation. It was a large plate / bearing wall because the staggering of the column joints and the very deep spandrel panels/beams which were extremely effective in redirecting vertical loads around missing/damaged facade columns. It was dense not open and at the time some believed this also made the high floors feel more secure with smaller windows.
OK experts explain how one adds the ability to sustain a plane strike other than beefing up the amount of steel?
What would the difference be had he simply ignored a plane strike? Was this the same sort of design for wind shear?
Does flex mean that the joints have some "give" like an expansion joint in a bridge span?
We have heard many times that the towers were remarkably strong and were designed to take a plane strike... multiple ones one person stated and remain standing.
My sense is that the facade was like a huge membrane... that WAS a design innovation. It was a large plate / bearing wall because the staggering of the column joints and the very deep spandrel panels/beams which were extremely effective in redirecting vertical loads around missing/damaged facade columns. It was dense not open and at the time some believed this also made the high floors feel more secure with smaller windows.
OK experts explain how one adds the ability to sustain a plane strike other than beefing up the amount of steel?
How does the SEISMIC data show this? The seismic data may have recorded the impact which was transmitted to the ground via the frame and made it "shake"... ergo seismic data. How does seismic data show anything other than perhaps the energy of the plane strike and the ability of the frame to convey the impact to the foundations?
If the same plane hit the AmEx tower there would or would not be the same seismic signature on impact? If it's different... what would account for it?
Crazy Chainsaw
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The perimeter walls were ment to move, to dissipate wind energy as motion, this was known
at time of construction. The motion of the perimeter on the planes impact dissipated energy,
Reducing the seismic signal transmitted to the core columns.
Understanding the energy flow patterns though the structure gives a glimpse to the unseen
Dynamics of the impacts initiation and collapses.
If you take the energetics far enough you can understand the collapses right down to the
Intergrandular connections of the Iron to Iron bonding of individual steel grains in the crystal
Latices.
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For sure the engines and landing gear in the nacelles penetrated the facade... The fuel in the wing tanks was massive... at something like 1 ton per cubic meter more or less... this "fuel" busted through the facade very easily... but was also disbursed on impact and clearly was all of the place and ignited inside and outside the tower. It's a fluid dynamnics calculation to understand how the fuel in the wing tanks would behave. And this is above the pay grade of this forum I suspect.
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I think we could say that if the tower were very stiff and not well anchored and the impact was large it could conceivably be knocked over... like the light poles at the pentagon were... In reality this is not possible / probable because YES the steel does flex and the joints do allow for movement. Because of thermal expansion... designers have to design in the ability of the structure to slightly expand when it is hot. My hunch is that almost any high rise would perform about the same upon a plane impact. But it would depend also on how much IMPACT took place.
If the "money parts" of the plane hit the structure all the lateral motion would push the structure (and destroy the columns hit).... which would or would not spring back and begin to oscillate like a tuning fork. But it's possible that only some "money parts" would impact the structure and perhaps others would "fly" right through the building as engine parts did on 9/11. Or maybe they could impact/destroy AND fly through the building. A jet engine COULD fit between the standard floor to floor height and between typical column spacing. It's not likely that all the heavy stuff misses the structure. But one can super impose the plane profile... project a straight path and see what gets hit... and probably destroyed.
If you take the twin tower facade columns... on a side... 59 and redistribute them throughout the OOS floor and building perimeter... not changing their total cross section (axial capacity)... you will have a standard field of 24 columns.
Here's a quickie sketch with a more standard column arrangement and AA11 flying into the building as it did on 9/11. Based on the sort of damage done to the 1wtc probably 6 (maybe only 4?) of the 24 columns would be lost. 4 are in direct line of impact of the heavy landing gear parts. But it looks like the core would take the same sort of damage...6 lost columns.
How would this scheme do? Would it fall down on impact? Or would it shake and survive? Would it do better or worse than 1wtc?
Guess.
Attachments
Clue... it is IMPOSSIBLE with our technology and the mechanical properties of building materials for a tall or large structure to NOT MOVE or "FLEX" as you call it. ALL MATERIALS OF THIS SLENDERNESS RATIO /CONFIG WILL FLEX - this was not "DESIGNED IN" but CONSIDERED and in some cases MITIGATED because swaying buildings are not good working environments.
ALL applied forces travel through the columns and interconnecting bracing beams... and through the floor plates... whether it is gravity or wind or a something that hits the building. Where else could the forces be "traveling"?
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What would have happened to the energy of impact in a welded connection facade?
Crazy Chainsaw
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It is the reason the perimeter columns were not welded but bolted, the core and core columns limited sway.
The perimeter columns were designed with a limited amount of movement and the core provided stiffening.
Oh and yes I understand the reason for considering harmonics in the design and harmonic dampeners.
Crazy Chainsaw
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You would have induced weld damage in core columns to an unknown existing, near the impact zone that could have been fatal to the design.
Dave Rogers
Bandaged ice that stampedes inexpensively through
It's a matter of record that he did no such thing, as I understand it. After the design was more or less complete, a political campaign to block construction of the towers raised the question of an airplane strike, and Robertson responded by calculating the response of the structure to an impact of the magnitude expected from a 707 travelling at slightly higher than stalling speed (simulating a plane lost in fog on a landing approach, because otherwise it wouldn't be that low). No specific account was taken in the design stage of such an impact.
Dave
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