posted on May, 18 2013 @ 03:35 PM
Originally posted by exponent
So please state this explicitly so I can save the link for future reference. You are saying here that fire affected trusses in the WTC can fall into
tension and exert an inward pulling force on the columns, yes?
No, the trusses do not sag into tension when they are SAGGING. How can truss be both sagging from heat and fall into tension? That would be an
The PDF PLB supplied explains quite well what happens, but you have to read and understand it.
The problem here is that you are not quoting from a study that investigates the effects you are talking about. The study is of a steel
beam, not a truss. They are radically different structures and that is why the paper I linked you to is a study of representative
trusses from the WTC, a much more specific study and conducted in part by the same firm (Arup, who are pretty well reputed).
But wait, that PDF was perfectly fine when PLB tried to use it to prove the hypothesis. So now I have shown he was wrong, suddenly it's no good
because it says beam instead of truss? Hilarious.
That is truss deflection, I have already said trusses can deflect, that is not the argument. What can't happen is that deflection pulls in columns.
You are making an uneducated assumption.
This is a woeful misunderstanding of the beam study. It does not purport to investigate the conditions of columns or a representative
structure. It is a technical paper on improvements in simplified simulations. This seems to have escaped you.
Yes it does. So why did PLB try to use it then? Maybe you should be debating him and his claim?
Luckily there's a way we can easily resolve this. You've referenced this paper as a reliable source and imbued it with authority which
inherently transfers to its authors. In this case I happen to know of another paper produced by Ian Burgess and Roger Plank. It is designed to study
trusses not beams and is an investigation into their behaviour, not a simplified model.
LOL OK then find a paper that says trusses and not beams eh? I didn't bring up these papers, you guys did.
All science tests use simplified models, now you are just making lame excuses to ignore, and deflect my points.
You can find it here: www.sciencedirect.com...
I believe it can also be found online for free as a PDF.
Oh yes another article you don't understand.
Here is what it says....
A numerical investigation of the structural behaviour of long-span composite truss systems, typically used in multi-storey floor construction,
under fire conditions is presented. The non-linear finite element program, Vulcan, which has been specifically developed at the University of
Sheffield for the analysis of structures at elevated temperatures, has been used extensively throughout. The in-fire performance of both restrained
and unrestrained composite trusses is determined. The contribution of each group of members (i.e. top chord and slab, web members, bottom chord and
supporting column) is investigated whilst considering various parameters such as the level of fire protection, structural modifications and deflection
patterns. It is shown that, for a truss which is restrained against horizontal movement at its ends, the load-carrying mechanism undergoes a
transition from bending to catenary action. Furthermore, at elevated temperatures there is a possibility of progressive buckling in the compressive
web elements, which may not have been the identified failure mechanism in design. This is seen to be initiated by a significant rise of the thermal
stress in the web members located within the high-shear zones towards the ends of the truss. The knowledge obtained is suitable for use when
implementing performance-based design.
It doesn't even mention columns, let alone that a runway deflection of beams, or trusses, would pull in the columns they are attached to.
BTW you didn't go though all my quotes, you addressed one, which you are wrong about.
edit on 5/18/2013 by ANOK because: (no reason given)