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Ozeco41's Response to a Challenge to Explain Initiation

Analysis, observations and theory related to initiation.

Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Tue Jun 28, 2016 4:26 am

Explaining the Twin Towers "Initiation Stage" Mechanism.

Earlier today I responded to this comment by SanderO posted in The Pub:
SanderO wrote:Would be nice if this forum could tackle initiation... in the twins...
...Initiation is more "unseen" and so there would be more guessing... and less ability to test and model... and not based on "data". Scares folks off????


This is my response - it is the start of a qualified (i.e. not quantified) explanation of the "initiation stage" mechanism - as presented it applies to both Twin Towers.

I will be drawing on material I posted on ISF in May 2015 when I responded to this challenge from a lay person member "Jango":
It would be a welcomed occurrence to be casually "walked-through" the technical aspects because as I've said before, my hang up is the initiation sequence, such as, What Had To Fail To Cause The Global Collapse.


So I intend to slightly edit my posted material to remove the forum specific bits and bring it here for SanderO and anyone else interested.

The first post set down my objective and rules of engagement - essential in the ISF environment. It is somewhat edited so I wont "quote" - I will hi-lite the edits for this OP post only:

My Objective - to explain the cascade failure process of WTC1 and WTC2 "initiation stage" up to the point where the Top Block was falling AND ROOSD/Three Mechanisms progression was under way.

I will not be addressing CD claims which means that I must allow for CD options in the mix of contributors to collapse. The understanding of cascade failure is not affected whether or not there was CD. (Think about that before (any of) you ask :))

And at least note my "Procedural Ground Rule #1" :)


My Procedural Ground Rules:

1) It will be my explanation. Not relying on NIST, Bazant or any other authority;
2) My objective for this stage of discussion process will be that any potential reader comprehend the form of "cascade failure" which initiated the collapses of both Twin Towers;
3) I will leave the possibility of CD in the mix to avoid pre-emptive strikes from either "side";
4) I will start from known facts which should be points of agreement;
5) I will progress in steps - advancing to the next step once we agree on the current step as soon as I get the energy;
6) My process will include explanation of some aspects of engineering which are critical to progress of the cascade failures and which are commonly misunderstood in these discussions;
7) I will be looking for agreement and understanding of the points I make - not vaguely stated or more global counter assertions which are not specifically directed at the points I am making; AND
7) It will be qualitative - not quantitative.

So those are my ground rules - << does any member care to comment?

Step One - Defining and Agreeing the Scenario.


The overall scenario for collapse initiation extends from "aircraft impact" through to "Top Block" falling bodily. The sequence and key points being:
A) Aircraft Impact caused damage and started fires;
B) Damage accumulated as a consequence of fires and any CD which may have been performed;
C) The damage increased to the stage where the "Top Block" started to descend bodily;
D) We may need the intermediary step of "Point at which remaining columns are no longer able to support top block". (Which led immediately to failure of all those columns which has survived to that point.)
E) Top Block descending bodily marks the end of our interest for this topic. (I will take it to the point where "ROOSD" driven progression is under way.)

Do any members wish to comment or disagree that those five identify/scope the scenario? Do any members have any additions that they want to add to define the scenario?

My initial plan - which I didn't stick rigidly with in the original; version - so expect adjustments on the fly - I willgo on to explain:
P) The failure is in vertical load carrying - vertical load carrying is the function of columns - failure of columns is therefore the main contributor to collapse initiation - and we have two main reasons for failure viz (i) cutting by impact or CD and (ii) failure in axial overload.
Q) Understanding the balance of factors in failure by axial overload- that is the one place where temperature will be relevant and it is a column by column specific balance of factors. (But we dont need to know the details for every column...we only need generic understanding.)
R) Concepts of "load redistribution" which are central to cascade failure - including why they must be understood in 3D and why load redistribution does not proportionately follow the proportion of already failed columns.

Those will do as starters. Without doubt we will identify more as discussion progresses.

Any comments so far on:
X) The procedural basics - I will be presenting my explanation NOT responding to other person’s ideas of their own explanation; AND
Y) The starting points for the scenario?

And I'll drop the highlighting of the edits for any subsequent posts

That deals with all (most??) of the procedural and disclaimer stuff. Work calls - I'll post the first bit of technical context next opportunity I get.



Have a bit of a chuckle over this from the original:
PS - add this in somewhere - "As I progress I will identify common misunderstandings which my explanation should help correct. I'll make them anonymous - without fear or favour to which side the errors come from." :)

And I know I'm not the only pedant around here so:
PPS - several bits of terminology including "falling", "descending" and "Top Block" have historically caused some pedantic nuisance. Tough - I'll leave them in and deal with any issues if and when they arise. F'rinstance I'm fully aware the the Top Block was NOT rigid. :roll:
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby SanderO » Tue Jun 28, 2016 1:17 pm

Long post...

Ground rules..

I think presenting YOUR take is what this should be about.
Qualitative is all one could do... There is no actual data from the impact to the top drop aside from some IB, jets, smoke plumes, and fire and the antenna movement. What can be "deduced" from this or what explains them much align with the initiation "process".
YEAH let's ignore Baz and NIST et al.

Step One

ROOSD may begin earlier that the top drop. It depends on how you define the "elements" of ROOSD... for example would local internal floor collapse in the top be a ROOSD attribute?

There is a step between fire and structure damage... ie fires cause mechanical damage... such as dropping members... the dropping members cause additional mechanical damage. No?

P) that's the release moments... for sure... loss of axial capacity. But what are the ways that axial capacity can be lost? You omitted mis alignment and loss of bearing.

I think you need to consider:
impact of heat on lateral members
impact of expansion/contraction of connections
role of the belt girder is any
role of the hat truss if any
role of the stiffer heavier mech floors and superimposed live loads

Floor slabs were not efficient load redistributers... or if they were... explain

parts of the top block were "rigid"... the facades were pretty rigid planes, as were the floor plates.

What descended in the visible top drop? just the facade? The facade and some attached floor plates? Parts of floor plates? Core columns and core floors?

Good start.
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Wed Jun 29, 2016 1:51 am

SanderO wrote:Long post...
Bound to be - because I'm reposting what is already in public domain AND because I will not water down the technical reasoned explanations at the risk of damaging meaning.
SanderO wrote:Ground rules..

I think presenting YOUR take is what this should be about.
Qualitative is all one could do...
I'll take that as "Agree so far to procedural setting."
SanderO wrote:There is no actual data from... the facades were pretty rigid planes, as were the floor plates.

What descended in the visible top drop? just the facade? The facade and some attached floor plates? Parts of floor plates? Core columns and core floors?
You points noted Sander - I'm reasonably well aware of your favourite themes and issues. BUT my preference/intent is that this thread topic be a presentation of and discussion of my explanation. Not wide ranging discussion of alternatives which do not directly impinge on my reasoning.

SanderO wrote:Good start.
Thanks.
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Wed Jun 29, 2016 2:01 am

Stage #1 - Where we are heading.

The next two/three stages of explanation will be:

Stage 2 Cascading Failure of Columns.
Establishing sequential column by column failure as the dominating feature of the cascade failures and starting to set the grounds for it being essentially a column by column process - starting to expose some common errors resulting from assumptions of global homogeneity.

(If I drop the "big words" I mean things like (i) assumptions that all the steel had to be heated to failure temperature - a recurrent false 'meme' in 9/11 CT discusion - reality is not so - stated overly simply the only column which needs to be heated at any time is the one that will fail next OR (ii) assumptions that failure of a proportion of columns results in proportional redistribution of load to all remaining columns - it doesn't and the real result is always worse.)

Stage 3 Engineering Bits #1 - Load Redistribution.
Some engineering - getting the basics of load redistribution on the table. Easy in principle but quite complicated in full 3D + T(ime) distribution including heat movements - I'll try to avoid going there.

(Stage 4 - Probably "Where does heat fit into this process?")
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Wed Jun 29, 2016 2:12 am

Some posts are not carried over.

(The original Thread on ISF at this point has several procedural comments and points for clarification raised by the original "Layperson Target" - Jango.


They are not relevant to this discussion on this forum and I have omitted them - members can raise their own on topic issues.

The original is here: http://www.internationalskeptics.com/fo ... p?t=292837 )
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Wed Jun 29, 2016 2:31 am

Stage 2 - Ozeco's Explanation of Twin Towers Initiation.
This stage should be relatively easy. Stage 3 will be more challenging. (remember the original target audience was one specific "layperson")

Aim of this stage of my explanation: Establish shared understanding - ozeco and interested members - that it was a process of sequential cascading failure of columns which initiated the Twin Towers collapses at the WTC on 9/11.

(Procedural comment: Much of this may be obvious and easily agreed but I want to put down all the necessary steps of logic. I will mark each <<Point for Agreement - which may initially be a point for further explanation. ;))

For purposes of explanation the Twin Towers 9/11 collapses fall into two stages of collapse mechanism.

The first stage - which I call "initiation" - was a cascading sequential failure of columns in the "impact damage and fire zone" for each Tower.

Initial damage due to the 'plane impact cut some columns and other bits of structure and started fires. The fires caused further progressive damage.

(There may have been some CD activity in this location at this time - see my ground rules.)


Damage accumulated to the stage where the Top Block descended bodily. << Should be agreed common ground


The second stage - AKA "progression" falls outside the scope of this explanation.

So at the end of the initiation stage all the columns had failed and it was failure of columns which allowed the "Top Block" to "descend bodily".

Other members - floor joists etc - may also have failed BUT the vertical load carrying columns are the ones which, by failing, allowed the Top Block to fall. << Cannot agree this YET - I haven't posted the reasons. :)

And that is the end point of our discussion - we now need to retrace our steps to work out the why and how.


Outline of Reasoning.

I have asserted - so far without proof - that it was a cascading failure. So what is a cascading failure and why were these two failures cascades?

The essential feature of a cascade failure is that it is a sequence of failures where as each item fails it passes load onto the remaining surviving members. Toppling a row of dominoes probably the simplest and commonest example of a sequence but with no load transfer. You may be aware of electricity grid failures such as the one which affected NE USA and Ontario in 2003. That was also a cascade failure which resulted in sequenced failures due to load transfer. Both of those are simpler in concept than WTC - they are each examples of binary steps - yes/no at each point. WTC 9/11 was several levels more complicated - each step was multi-factor analogue - explanation coming in Stage 3 - but same underlying principles. Sequence and load transfer causing further failures.

The option to a sequenced failure is that all members fail simultaneously - that didn’t happen as shown by the minutes of delays between initial observed motion - settling - tilting then dropping. Damage such as the inward bowing of perimeter being evident some minutes before the end.

So it was a sequence of column failures.

The second part of the proof of it being a cascade is that each failure passes load to other members - the process of redistribution. That should be a "gimme" - there was a fixed amount of weight onto the columns - one column stops holding its weight - something has to hold it.

So there was "load redistribution". We will explore how that works in Stage 3.


Summary of points made:
(i) Failure of columns defines the process; <<Point for Agreement
(ii) During this stage all columns failed; <<Point for Agreement
(iii) allowing the top Block to "fall" (Get lower - descend - it wasn't "free fall" :roll:; <<Point for Agreement
(iv) Three causes of failure - axial overload, cutting by aircraft or CD. <<Point for Agreement

Any members interested in discussion can either indicate agreement or identify any of those four needing further explanation?

My objective is to resolve any bits that are unclear - before proceeding to the next stage which gets harder. :roll: :?

And the main question - in order to set an agreed foundation for further discussion - is this:
"Do you agree 'that it was a process of sequential cascading failure of columns which initiated the Twin Towers collapses at the WTC on 9/11' "?
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby SanderO » Wed Jun 29, 2016 9:31 am

ozeco41 wrote:[b][u]...
(iv) Three causes of failure - axial overload, cutting by aircraft or CD. <<Point for Agreement
...


I mentioned a 4th column failure mode... mis alignment of column ends. This could happen of one of the columns is pushed by an expanded beam... or mechanically impacted by some "thing"... causing the column to column splice to yield and the ends to slide passed on another... Now there is reduced bearing area and failure... similar I suppose to "cutting" a bit from the column cross section.

I say this because in the cascade failure the core is coming apart and in so doing one would expect some "collateral" damage to other parts of the intact structure.

If the cause of end displacement is largely from expanded beams heated from fires... this allows for even cold columns to fail from a fire/heat cause...without direct application of heat to the column. Also unrestrained column end connections are more subject to lateral displacement... This was the case in the twin towers. AND if there was local floor and beam collapse the column would also lose lateral bracing.

The plane cut columns happen at outset... load distribution failures are cascade type... CD is over course undefined as a failure mode... even when it was supposed to have happened.... Would that be to cause "release"? or part of a sequential process destroying OAL capacity?
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Thu Jun 30, 2016 9:24 am

Sander - can we make sure we are singing off the same sheet of music - or - more apposite - "Following the same road map"? I think you are getting ahead of my explanation.

So let's check: Sander do you agree that:
(a) The "initiation" stage was a cascading failure of columns which dropped the Top Block"? AND
(b) (i) Failure of columns defines the process; (ii) During this initiation stage all columns failed; THEREBY (iii) allowing the top Block to "fall"?

If we are agreed that such is the scenario for further discussion THEN:

Your first comment::
SanderO wrote: I mentioned a 4th column failure mode... misalignment of column ends.

I'm aware of that one. I intend to identify several ways that columns were overloaded to lose capacity for the original axial load. Including (i) Load Redistribution; (ii) Increased critical length due to loss of bracing; (iii) effects of heating; (iv) eccentricity of loading; (v) bending out of alignment AND - add in your favourite and any others that come along. :wink:

In the structure of my argument yours is NOT a 4th "Mode" - it is one of the several options I intend to discuss in the next stage(s).

And your extra comments are "jumping ahead" - we haven't got the foundations stages agreed YET. :wink:

I'll edit and post the next stage as soon as I get a bit of quiet time. :)
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby SanderO » Thu Jun 30, 2016 10:56 am

ozeco41 wrote:Sander - can we make sure we are singing off the same sheet of music - or - more apposite - "Following the same road map"? I think you are getting ahead of my explanation.

So let's check: Sander do you agree that:
(a) The "initiation" stage was a cascading failure of columns which dropped the Top Block"? AND
(b) (i) Failure of columns defines the process; (ii) During this initiation stage all columns failed; THEREBY (iii) allowing the top Block to "fall"?

Of course... this is correct.

If we are agreed that such is the scenario for further discussion THEN:

Your first comment::
SanderO wrote: I mentioned a 4th column failure mode... misalignment of column ends.

I'm aware of that one. I intend to identify several ways that columns were overloaded to lose capacity for the original axial load. Including (i) Load Redistribution; (ii) Increased critical length due to loss of bracing; (iii) effects of heating; (iv) eccentricity of loading; (v) bending out of alignment AND - add in your favourite and any others that come along. :wink:

In the structure of my argument yours is NOT a 4th "Mode" - it is one of the several options I intend to discuss in the next stage(s).

And your extra comments are "jumping ahead" - we haven't got the foundations stages agreed YET. :wink:

I'll edit and post the next stage as soon as I get a bit of quiet time. :)


OK
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Thu Jun 30, 2016 1:16 pm

Thanks Sander.

Now in the original discussion my "audience of one" was showing clear signs that he was thinking the processes were "one big whatever" - the same sort of error that T Szamboti and his debunker allies make with the "Drop to Impact" false premise of "Missing Jolt".

So I was considering "training aids" and this post resulted - it still bridges a gap in the explanation so here it is - more or less unedited:
ozeco41 wrote:(Preface to) Stage 3 - Ozeco's Explanation of Twin Towers Initiation.

- we need some visuals or training aids:

How comfortable are you using metaphors or analogies??

Lets try one. I've already said that a cascade failure is not about "one big force" acting on "one big object" (Or words to that effect.) It is more a series of little bits of nibbling at the edges - the little bits adding up to affect the whole. And in the WTC Twin Towers ignition cascade those bits added up in such a rush that it looks like one big effort. Not so - it was an extremely fast series of (relatively) little bits of nibbling at the edges.

So let's try a metaphor - if it is not your scene we can drop it.

Think of an icebreaker ship. It cuts a path through ice floes by nibbling bits of the edge. By shoving its bow up onto the ice floe and breaking bits off the floe. One section at a time. It doesn’t try to do it in one step.

By contrast what would happen if the ice breaker rammed full speed into a solid iceberg? Would the berg split in two? Or would the icebreaker end up with a bloodied nose? (Yeah - OK I mean a dented damaged bow. Loading metaphor on metaphor may not be a good tactic... :o :oops: )

Now the WTC Towers initiation stage of collapse were cascade failures. And a cascade failure is little by little - step by step - NOT "all at once in one big bang".

Sure those cascade failures were very fast - seconds only overall for the main failure part of the process - which was probably hundreds of distinct steps. BUT fast or not the mechanism was very definitely a sequence of steps. Each one dependent on the one before it to give it a "kick off". as the icebreaker breaks each bit off the edge of the floe it clears its path to get at the next bit, Then the next...then the next.

Change the metaphor - picture a row of dominoes set up to topple in sequence - push the first one and the second falls then the third then the.....

The WTC cascade failures - thousands of times larger scale than a row of dominoes, orders of greater complexity still ran at about the speed of a row of dominoes. If anything faster.

OK Pause there - do those metaphoric analogies help or hinder? If they help -- great we can use them. If not I will obviously need to use different "training aids". :o

The point I am trying to get across is that a cascade failure is not one big step, one big force, one big bang. It is a sequence of relatively little steps/forces/bangs.

Can you think of it as a lot of relatively little steps in rapid sequence?

My audience at that time was happy with the metaphors AND understood the key point of "little by little".
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby SanderO » Thu Jun 30, 2016 4:15 pm

Of course the line of dominoes is not perfect by a long shot... it progresses through time but each even is the same... You can create domino analogies which:

branch off into several lines
escalate in size... ie the first domino can't topple the one 10 interactions away... but it topples the one that leads to another that leads to another and each is escalating in "scale" so to speak.

The ultimate failure was across the plan... leading to top tilt/drop. But what about failures propagating vertically... up or down? Why not?

++++

At one point someone noted that the collapses were about failed "connections". My take was that the "connection" was made up of smaller elements which could also experience progressive cascade failures until the connection/joint fails... the beam drops oe the column buckles. We can't know what was happening at that level... but perhaps we can know that it WAS happening at that level.

We're into straw that broke the camel's back territory... no?
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby pablonovi » Thu Jun 30, 2016 8:17 pm

Oz,
I've read this entire forum including, naturally, all your posts here, and, imo, this thread represents your best work (or, "most useful towards helping people understand the 3 building collapses related things").

A couple of things / tendencies that stand out hugely favorable to me:
1) You don't START OUT by ruling out CD; but instead allow for that possibility;
If the CD/CT position turns out to be wrong, your approach here is a great way (the best way?), so far, towards eventually either convincing us Truthers that we've had it wrong, or convincing the Debunkers that they've had it wrong.

2) Your systematic, step-by-step approach, to both the overall (pre-)initiation phase & little-by-little cascade-process within that phase.

Please proceed ...
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Thu Jun 30, 2016 10:01 pm

SanderO wrote:Of course the line of dominoes is not perfect by a long shot... it progresses through time but each even is the same... You can create domino analogies which:

branch off into several lines
escalate in size... ie the first domino can't topple the one 10 interactions away... but it topples the one that leads to another that leads to another and each is escalating in "scale" so to speak.

The ultimate failure was across the plan... leading to top tilt/drop.
Agreed - see the opening comments of the next stage.
SanderO wrote:But what about failures propagating vertically... up or down? Why not?
yes but mostly outside of the scope of initiation OR doesn't change my explanation of initiation.
SanderO wrote:At one point someone noted that the collapses were about failed "connections". My take was that the "connection" was made up of smaller elements.... but perhaps we can know that it WAS happening at that level.
Yes but it is micro level detail below what I need for the explanation at this stage.
SanderO wrote:We're into straw that broke the camel's back territory... no?
The full load of straw broke the camels back - we know one last straw triggered the failure - we don't need to know which straw it was other than it was the "last one". And it is an exact analogy Sander. We know that ONE column triggered the cascade. We will never know which column. We can be sure it was affected by heat OR cut by CD.
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Thu Jun 30, 2016 10:04 pm

pablonovi wrote:Oz,
I've read this entire forum including, naturally, all your posts here, and, imo, this thread represents your best work (or, "most useful towards helping people understand the 3 building collapses related things").
Thank you
pablonovi wrote:A couple of things / tendencies that stand out hugely favorable to me:
1) You don't START OUT by ruling out CD; but instead allow for that possibility;
My deliberate choice to keep the logic rigorous.
pablonovi wrote:Please proceed ...
Next stage coming soon.... :wink:
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Re: Ozeco41's Response to a Challenge to Explain Initiation

Postby ozeco41 » Thu Jun 30, 2016 10:18 pm

Ozeco's Explanation of Twin Towers Initiation.

Progress review.

I have explained that the key to understanding of cascade failures at WTC is to recognise that it is a sequence of individual column failures. Somewhat akin to toppling a row of dominoes. Once the first domino topples the impetus to the next comes from the limited stability of that second domino PLUS the impact of being struck by the first. And so on down the line.

We easily see the "row of dominoes" as a sequence of individual topples. We need to take the same focus in our understanding of WTC cascade failures. See it as a sequence. Maybe several concurrent sequences - those big domino toppling demonstrations usually have multiple branches. The principles remain the same.

So for the next column in sequence to fail in axial overload requires that the load applied be more than the strength of the column can support. In the WTC situation that involved a varying mix of two factors:
(a) Increase the load; AND
(b) Weaken the column (Not by CD cutting - those ones - if any - are not failures in axial overload)

And in these next three stages I want to explain:

Stage 3 - how loads redistribute following a failure of a column and increasing the load on remaining columns. And specifically why the added load is ALWAYS more than most persons would expect.
So this post is mostly about "(a) Increase the load";

Stage 4 - Why columns fail - a specifically how (i) increasing unbraced length; (ii) heat (temperature actually); and (iii) creep weaken a column.
So the next post in the sequence will be mostly about "(b) Weaken the column"; AND

Stage 5 - Perimeter Inward Bowing" - one of several examples of multi-factor physics which both "sides" have misunderstood.


Stage 3 - Load Redistribution - Why it is not "proportional" and (almost) Always Worse.

The history of WTC 9/11 collapses is littered by presumptions that removal of half the columns would double the load on those remaining. Removal of 25% would add 33.3% extra load uniformly to the remaining columns.

That is not so. The redistribution of loads depends on the original layout of the columns and the locations of those removed and those remaining. I want to avoid the full engineering explanation but can provide it if needed.

So I will use two simplified examples/thought exercises to illustrate.
(I've already posted them in the Peanut Gallery - but now I give the answers)

Example/Exercise #1

This is a simplified WTC Tower - simplified to three rows of columns. Left Centre and Right.

Image

BEFORE the column was cut the total load in each of row L and Row R is 100 whilst Row C has 200.

Now some nefarious b..... cuts Row R.

Obviously the load in "R" drops to zero.

Not so obvious maybe?? The load in "L" also drops to zero - leaving "C" carrying the unaltered total load of 400. Nothing proportional about that - cutting 33.3% of columns leaving 66.7% intact and the load on one column DOUBLES.

Now understanding that is second nature to engineers like me but it may be new to other members. Do you see why it is so or do you need further explanation? <<Point for Agreement or further explanation

Example/Exercise #2
Image
Seven rows of columns A>> G Equally spaced (no snide comments about my graphic skills - I'm not C7 using MSPaint.) All same load - make it 100 if you must have a number.

That same nefarious b..... Cuts Row "D"

Assume that the "Top Block" is a steel frame with the limited elastic flexibility that such a frame would have.

What happens to load in rows B, C, E and F?

This is what happens:
Image
(Excuse the simplified graphics.)
The dropping at "D" causes the upper structure to "hog" over C and E AND it tries to lift over B and F.

I cannot say "how much" without doing the full specification of the structures and an FEA analysis. We don't need that detail here - just the principles it reveals.

But sufficient for us to show that the loads on B and F REDUCE and the loads on C and E increase by half of D PLUS the amount of the reductions on B and F. So the two columns adjacent to the one which was cut received additional load which is MORE than was carried by the cut columns.

And that is as complicated as we need to think about.

BOTTOM LINES for this Stage 3 of explanation are:

A) Failure of any column will cause the load it was carrying to be redistributed to other columns:
(i) It will add load to some, add less load to others and may actually REDUCE load on some;
(ii) The redistribution will not be proportional to number of columns failed; AND
(iii) Will cause a disproportionate increase in load for some columns somewhere in the layout - not necessarily the adjacent columns.

B) The disproportionate transfer will drive some of the remaining columns closer to failure than others. And it will almost certainly be worse than would occur with proportional reallocations.

Are you (i.e. any member) comfortable with understanding those "bottom lines" A)(i), (ii), (ii) and B)? <<Points for Agreement or further explanation
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