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15th October 2015, 07:42 AM | #1 |
Penultimate Amazing
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OOS Collapse Propagation Model Part II
Which structures are designed to "not go 'runaway'"? Please be specific. In all my years as a structural engineer, I've never designed a structure to not go "runaway", nor have a read a published document advising engineers to do so, nor is it standard practice anywhere I've worked or studied.
There are two goals in strength design. First is to prevent a failure under extremely unlikely chance of exceedence loads. The second, and this doesn't apply to all members or all materials, is to ensure a ductile failure mode, so that the inhabitants can tell that the structure is in distress and have time to either fix the problem or evacuate before a collapse. Or are you trying to refer to progressive collapse? |
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15th October 2015, 08:48 AM | #2 |
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Progressive collapse which will take out the entire structure. Obviously some structures are more likely to have a catastrophic failure. But if you take a cable suspension bridge like the GWB... It can probably be "OK" if one cable (not the main ones.. but the vertical ones... fails. A main cable failure would doom the span.
When you have elements such as a few transfers... which could fail the whole building.... or a system like the floor plates which braced the columns and not means engineered in to isolate or arrest the collapse it can take the whole building with it once it "gets going". |
15th October 2015, 09:00 AM | #3 |
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No one designs structures to arrest once they start. The primary design philosophy is simple: design members such that they can always resist the forces applied. Progressive collapse mitigation is done with prescriptive methods: positive connection between elements (no more Ronan Point type failures!) and newer IBC requirements for structural resiliency that specify a horizontal design force of some percentage of the vertical design force.
Floor plates, or diaphragms in engineering parlance, deliver horizontal forces, typically wind and seismic but also impact for the case of the WTC to the lateral force resisting system. Are you suggesting the need for a completely redundant diaphragm? |
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15th October 2015, 10:17 AM | #4 |
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Since a new thread was started I's like to give a summary of the OOS model thread so far:
I originally started the thread in May, 2010. The thread was immediately met with a 'knee-jerk' reaction appeal to Bazant's paper BV (2007). The same pattern was repeated over the next 5 years throughout these threads: OOS Collapse Model Applicability of Bazant's model to the real world Bazant's crush-down/crush-up model A post with sample quotes about Bazant from page 1 to 13 given by JREF/ISF regulars a this link: My early comments on BV responding to this were reproduced at this link: A summary of the views expressed within the first 13 pages by some of those considered group leaders are reproduced below: Newtons Bit comments R Mackey comments Dave Rogers and Myriad comments Newtons Bit has an MS in structural engineering. R Mackey identifies himself as a 'rocket scientist' who works (or worked) for NASA. Dave Rogers has a PhD in physics. Myriad is a moderator in this forum. TFK, who also had much to say on the subject of BV and BL, is an engineer and active poster. And, David Benson, co-author of BLGB, has a PhD in mathematics. Bazant has a PhD in Structural Engineering. Therefore, you are not looking at just a few exceptions. You are observing the behavior and mentation of representatives of an entire subculture. >>>>>>>>>>>>>>>> The thread went dormant and was later revived on page 44 at this link. I revived the thread in June, 2014, so that I could test to see how deeply these opinions about Bazant's BV, BL, and BLGB were still held. The views originally expressed near the beginning of the thread were still held strongly and defended by the participating posters with almost no exceptions. >>>>>>>>>>>>>>>> The thread was later revived on page 67 linked here in September, 2015, for the same reason. At that time I presented a list of quotations from Closure to 'Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions' by Zdenek P. Bazant and Mathieu Verdure by Zdenek P. Bazant and Jia-Liang Le (BL), published in 2007. I also presented a list of 44 highly specific questions about information within the quotes presented. The quotes directly from the paper and the 44 questions are at this link. I also presented direct quotes from David Benson, co-author of What Did and Did not Cause Collapse of WTC Twin Towers in New York, by Zdenek P. Bazant, Jia-Liang Le, Frank R. Greening and David B. Benson (BGLB). The direct quotes are from an exchange he had with me after his paper was published. I also presented a list of 30 highly specific questions about information within these quotes. The quotes directly from David Benson and the 30 questions are at this link. The direct quotes and questions were carefully chosen to allow anyone with a sincere interest in the subject of the Bazant papers on the WTC collapses published from 2007 to the present to see these papers for what they really are. It is quite interesting to contrast the direct quotes from both Bazant and Le and BLGB co-author David Benson with collected statements which represent the way that this same paper is perceived within the JREF/ISF environment. These simple quotes and questions, directly contrasted with the JREF/ISF systems of belief as expressed in the collected quotations, can help the more sincere observers among the readers, truther, debunker, or more non-attached honest observers curious about the written history of the WTC collapses, to disabuse yourselves of the talking points to which you have been subject for years. This set of talking points, or 'memeplex', is so transfixed within this forum that it is now a permanent state. I sympathize with regular readers of this forum and anybody subject to environments like this since the atmosphere is one in which people are drowning in talking points, or memes, of their own creation. For this reason I've devised a simple step-by-step system in which I will use the Bazant and Benson quotes and directly contrast them with the collected JREF/ISF quotes. These contrasting quotes, along with simple questions about the quotes, may help some readers free themselves from the JREF/ISF talking points. Others, of course, identify themselves so deeply with the JREF/ISF talking points that they will defend the memeplex no matter what. |
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15th October 2015, 10:21 AM | #5 |
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I don't have a MS in structural engineering Major_Tom, nor have I ever claimed to have one. Where do you get your facts, anyways?
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15th October 2015, 10:29 AM | #6 |
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Thanks for the correction. I posted that info a number of times, and it is your first correction. What are your qualifications so i can edit my first post?
>>>>>>>>>>>>> Question: Why can't we quote people from the original OOS thread? I am not given the option to quote from the thread when I review the comments there. The only reason I could give the links in my first post is because I kept the records of the links. How can we continue the exchange from the last thread if we cannot quote comments from it? |
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15th October 2015, 10:34 AM | #7 |
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15th October 2015, 10:39 AM | #9 |
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15th October 2015, 12:14 PM | #11 |
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Sure, then everyone can see yet another example of how your posts are completely devoid of research and little more than thinly veiled and, still rather confusingly, incorrect personal attacks. You quote myself, Myriad, etc, to show how wrong we are, but just about everything about our statements still seems to be correct. Maybe one day you'll actually try to explain what you're getting at, but I'm not holding my breath.
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15th October 2015, 12:42 PM | #12 |
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A grid design doesn't have an OOS per se... The cores contain vertical shafts/ building services, stairs, elevators rises, bathrooms and so forth. The floor slabs are framed with supporting beams framed into girders supporting a concrete slab usually poured in a fluted metal deck.
Would plane damage as on 9/11 cause the same out come in a typical steel grid with no OOS in the same time frame as what happened to the LERA design with a column free OOS and no structural outer wall? There would of course need to be a wind shore structure... diagonals etc in the grid scheme. Would that have any impact on a collapse? |
15th October 2015, 02:14 PM | #13 |
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How is what is OOS and what isn't OOS determined? What if there was a 60' grid system? Can you explain where the cutoff is?
Quote:
Quote:
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15th October 2015, 02:51 PM | #14 |
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OOS would be what a hull and core design is... the space around the core... to the "hull" is column free. You know what it is:
"The tube system concept is based on the idea that a building can be designed to resist lateral loads by designing it as a hollow cantilever perpendicular to the ground. In the simplest incarnation of the tube, the perimeter of the exterior consists of closely spaced columns that are tied together with deep spandrel beams through moment connections. This assembly of columns and beams forms a rigid frame that amounts to a dense and strong structural wall along the exterior of the building.[3] This exterior framing is designed sufficiently strong to resist all lateral loads on the building, thereby allowing the interior of the building to be simply framed for gravity loads. Interior columns are comparatively few and located at the core. The distance between the exterior and the core frames is spanned with beams or trusses and intentionally left column-free. This maximizes the effectiveness of the perimeter tube by transferring some of the gravity loads within the structure to it and increases its ability to resist overturning due to lateral loads." ++++ Hat truss is really only carrying the 3 floor loads within it and the antenna above it. It is bearing ON the core. If core columns are destroyed it loses some of the bearing "area" and it's possible that the loads above the destroyed column then "hang" from the hat truss and presumable can be redistributed through the hat truss to other columns. The question is where the loads above the lost column can be carried by the column to column connections which are not designed as "hangers". Do you think 15 stories of loads above a destroyed core column will "hang" from the hat truss and be redistributed? I suppose you can do the math on the connections... |
15th October 2015, 03:29 PM | #15 |
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15th October 2015, 03:47 PM | #16 |
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I have no idea where you are going. Or maybe I do.
The engineering design for the tower met the code (as negotiated) and performed as expected under normal use. I was in them dozens of times. The issue is how they performed when they suffered some serious damage and fire fighting was virtually impossible. This is not an easy question to answer. However they came down awfully quickly and completely and I would assert this is likely related to their design... Do you disagree? |
15th October 2015, 03:52 PM | #17 |
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As long as we're asking question DGM...
If 6 adjacent columns in the core were severed by the plane....503, 504, 505, 506, 604 and 605 at floor 96/97/98.... what happened to the columns above them up to the hat truss? What percentage of the axial load had to be "redistributed? Where would redistributed loads likely go? |
15th October 2015, 03:53 PM | #18 |
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Key point. Failures which occur WITHIN the design parameter envelope are design flaws. Failures OUTSIDE the design envelope or code requirements are by definition NOT design flaws. Which doesn't change the bit of truth - partial truth - that Sander keeps raising. "did the design contribute to the ultimate failure?" Of course it did. The design was the dominant (set of) factor(s) which determined the mechanism of ultimate collapse. Always will be - what but the design determines where the weakest point is for any applied load? Put simply "So what?" - I've posted the more extensive explanation of that challenge several times. It is not just a matter of engineering - rather a mix of functional requirements, engineering practicality and commercial viability within the regulatory policy framework (and several other factors but those are the main ones AFAICS.) |
15th October 2015, 04:01 PM | #19 |
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15th October 2015, 04:08 PM | #20 |
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Hard to say... But YES... Buildings don't get to go through destruction testing or crash testing as autos. Of course because they are not moving objects!
But these extremely tall towers in NYC could be hit by planes flying instrument only in fog and the evening... This issue was raised and LERA did some sort of calculation. However I don't believe any calcs were done to see what happens with fire and so on... Doesn't that seem odd? |
15th October 2015, 04:08 PM | #21 |
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My post #18 "crossed in posting" with this:
Then why not state clearly what the "issue" is so we can stop going round in circles? What about "how they performed" are you trying to question? What question? AFAICS you haven't asked a question that can be answered. It is impossible to answer if you won't ask the question. Try stating - preferably in a single sentence - what question you want answered. 1, 2 Both agreed. More to the point I don't see anyone disagreeing. 3 Of course the mechanism of collapse was "related to the design". I would go further (and have several times) the mechanism of collapse was dominated by - determined by - the design. The question remains "So what?" No. For the umpteenth time. BUT who is disagreeing? |
15th October 2015, 04:12 PM | #22 |
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Can I infer that you believe they should have been designed to withstand the events of 9/11 (somehow)? Did the designers have the capability in the late 60's?
ETA: No plane would be flying as low as the towers on instrument at that speed (or any speed). Full fuel load you go somewhere else, not fly low and fast. |
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15th October 2015, 04:20 PM | #23 |
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So do I - AGAIN. "Negotiation" is a stock standard part of code application. The implication that it was underhand or dishonest needs addressing. IF the negotiated conditions were in part responsible for failure THEN that aspect is an objectively testable issue of fact.
BUT the person making the complaint has to assert that the negotiated standards were improperly agreed OR improper in technical standard. AND - in this setting - demonstrate that they somehow contributed to collapse. Which will be hard because the collapse occurred OUTSIDE the valid envelope of design parameters. As my opening bid I will assert that NONE of the negotiated conditions can be proven to be relevant technical errors under those conditions. My apology Sander - this bit was a drafting/proof reading error. |
15th October 2015, 04:31 PM | #24 |
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I don't know about negotiating code issues like design loads for office use. Code compliance is always squirrelly when it comes to renovations of old buildings which can often be filed under the old code when they were built for some items. But others must comply with the new codes.
I suspect the code reductions for the live load for office use was negotiated to save weight and save money. Saving weight in a building also means that there is less steel, thinner / weaker concrete perhaps. Does that mean too like too little steel? Who knows. But if the design loads were reduced there had to be a less "robust" structure. |
15th October 2015, 04:38 PM | #25 |
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15th October 2015, 04:55 PM | #26 |
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15th October 2015, 05:05 PM | #27 |
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15th October 2015, 05:09 PM | #28 |
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15th October 2015, 05:11 PM | #29 |
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That is already agreed.
I suspect that it was a reasoned decision in full cognisance of all the factors. And I wish you would stop implying malicious intent unless you are prepared to show how it could be relevant. (If it is not shown to be relevant it matters not whether or not it was "naughty cheating".) And...? You are the one repeating the claim. And there is enough evidence available for a reasoned argument to show how any of the known code variations may have been relevant. The buildings did NOT fail due to design flaws within the envelope of design parameters. So your inference of possible malfeasance has no where to go. Whether you are right or not it is irrelevant UNTIL you state clearly: a) how it related to the ultimate failure mode; AND b) Why anyone should be concerned about ultimate failure modes. You are persisting with your conflation of "within design" and "outside of design". Please don't. For future posts try the discipline of clearly stating "For this post I am reasoning WITHIN the design parameters" OR "For this post I am discussing out of design envelope overload conditions of ultimate failure". |
15th October 2015, 05:15 PM | #30 |
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15th October 2015, 05:24 PM | #31 |
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If 6 adjacent columns in the core were severed by the plane....503, 504, 505, 506, 604 and 605 at floor 96/97/98.... what happened to the columns above them up to the hat truss?
What percentage of the axial load had to be "redistributed? Where would redistributed loads likely go? |
15th October 2015, 05:28 PM | #32 |
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15th October 2015, 05:56 PM | #33 |
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15th October 2015, 06:00 PM | #34 |
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15th October 2015, 06:13 PM | #35 |
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I am not interested in addressing your questions... I am interested in furthering my understanding about how the buildings collapsed. You are incapable of that or unwilling.
I am not here to answer your questions. I have expressed many times my concerns, I have linked to other engineers who had similar concerns. If you don't think they are valid. .. so be it. I am not here to convince you, educate you or win debates. |
15th October 2015, 06:29 PM | #36 |
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15th October 2015, 07:01 PM | #37 |
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15th October 2015, 08:03 PM | #38 |
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Sander that has not been the focus of your recent comments. If you are interested in further explanation of the collapse mechanisms for the Twin Towers I can probably help. I am not interested in explaining WTC7
BUT "understanding the mechanisms" it is not an issue about what you seem to see as shortcomings of design. I and others have explained several times why the collapse mechanism - specifically that portion labelled "ROOSD": 1) IS a consequence of the design when pushed to the ultimate way outside reasonable design parameters; AND 2) Is not a "design flaw". So if you want to change your focus from "flaws" to "understanding the mechanism" simply say so. I can and will outline the overall mechanism and am willing to follow through with responses to more detailed aspects. PROVIDED you are prepared to take part in reasoned discussion without changing topic focus. AND that process will require asking and responding to questions WITHOUT changing the focus of discussion. The first comment is unfair and the second one unrealistic. If you do not understand something and want to understand it then asking and responding to questions is the way it is done - esp in this forum setting. Both DGM and I - probably many others are crystal clear as to the area of your concerns and the valid parts of those concerns have been answered several (?) times. You have also been challenged several times about the invalid parts of your concerns and reasons provided as to why your concerns are not valid. BUT your "concerns" are a different topic to "understand the mechanism" and the only overlap between the two is the common feature of the ROOSD sub-mechanism. Mmmm... let that pass. The "only' is not true - you have been pursuing vastly different issues than understanding of the mechanics. Decide which you want. Tell us - or me at least. I will explain or point you towards existing explanations of the mechanisms. I see no point in further discussion of your concerns about "design flaws" when reasoned explanations have already been posted. |
15th October 2015, 09:34 PM | #39 |
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Is this point clearly recognized within the written history of the collapses? Has anyone besides SanderO yet agreed with you that there are clear mistakes within the latter Bazant papers and within the quotes by David Benson provided earlier? Within the available Journal of Engineering Mechanics publications on this subject? (Bazant, Seffen, Eagar and Musso). Is there the slightest mention of this fact within the NIST reports? To what degree have you reviewed the written history to see if this point is clearly recognized? An excellent present day analogy is given to us in the case of the Fukushima nuclear meltdown(s). In that case: "Failures which occur WITHIN the design parameter envelope are design flaws. Failures OUTSIDE the design envelope or code requirements are by definition NOT design flaws." In the case of Fukushima, the failures occurred "outside the design parameters". The meltdowns are, therefore, "not design flaws". Likewise, there is little effort by the Japanese government to openly examine whether other reactors are similarly vulnerable. Open public debate on this issue within Japan has been effectively shut down. Large corporations with investments in nuclear power, who actively set "code requirements and design parameters" have no interest in public examination of other reactors or in an open, transparent review of future "design parameters". But "so what"? |
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15th October 2015, 09:37 PM | #40 |
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This is a miseadling and non-specific definition. You're using "open office space" to mean the floor between the hull and core of a tube within a tube structural system. But you're avoiding attaching a length of floor to it which makes it hard to figure out what other similar buildings to the WTC would have this "OOS" design flaw you're referring to.
Let's suppose that you're a building permitting official and a set of plans crosses your desk of a new mixed-use skyscraper with a hull and core system crosses your desk. Are you alarmed? Does this have the same design flaw as the WTC? What if the max span of floor beams is only 20' and it supports hotel rooms. Does it still have this "OOS" design flaw? Would you think it to be prudent to come up with a different term than "OOS" to describe this structure at that point?
Quote:
We also know that as the core columns deflected downwards (a natural effect of both the load reversal and creep), they pulled the exterior columns inwards until they buckled. I've done the calculations verifying that. |
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