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.