"proehling" <peter_roehling@eee.org> wrote:

"JMW" <jmwilliams@enforcergraphics.f2s.com> wrote
For good reason. Both they -and many other nut-groups such as the "We never
landed on the Moon" and the "Flat-Earthers"- all share the same pathology:
it's called "Owning The Truth".
See www.ocdonline.com/articlephillipson6.php

If you check Google, you'll probably find that I was the first one who
posted a link to that page.

the first scientific models
probably were those of bazant and zhou

they proposed the column collapse theory

which held that if one floor loses enough core column strength
possibly due the crash and fires
then that was enough to instigate a progressive collapse
in structures like the world trade towers

this is based on a basic inequality

if the energy released from the falling masses potential
during the fall of one story from rest
is greater than the energy used to pulverise and snap
the major structural supports enough to initiate lower story collapse
then the paper asserts
since next iterations mass and kinetic energy will be larger
it too will have enough energy to initiate lower story collapse

in the world trade towers
the center columns were the major structural support
and so if fire and collision were to lower
the central column's strength so one floor collapses
and that causes the impact to start another floor collapse
the process is necessarily complete

in their model
there is a basic separation into two components
an upper and lower

-----------
| | upper
| XXx |
XxxXXxxXXXxxx
XxXx XX Xx
| |
| |
| | lower
. .
. .

the lower response upon impact from upper
is modeled as a stiff spring
of stiffness approximately 71 GN/m
approximated from strength of lower columns

for the north tower 7
they calculate the upper mass as 5.8 x 10 kg
and make two calculations of overload ratios
at greatest 3.7m downward displacement on the stiff spring
an overload of 31
and initial impact overload of 64.5
whereas building infrastructure was built for 3-6 overload tolerance
( they state 2 and have been criticised for this biasing error )

however
in their fall time calculations
they discounted plastic energy losses
neglected all pulverisation energies
and neglected losses of mass from the upper section
from pulverisation and blowout

their initiation hypothesis requires at least 800 C temperatures
across the entire floor of collapse
which clifton and others have debated

and the fall will not distribute the load of the upper
in a single impact to spring response after the first floor collapses
as modeled in the paper
but crushes the bottom and distributes over an interval

cherepanov has shown that even excluding the plastic losses
even the standard pancake iterations must have geometric factors
of between '\/3 and greater to the fall time
and can be excluded by existing evidence of fall time

he suggests fracture waves
which would convert the initial impact into a progression of damage
that could effectively remove the dissipating forces

however
this model predicts a leading fracture pulverisation
and cherepanov incorrectly argues that this
would allow the building to collapse in the near free fall regime

the error is that the energetics still rob from kinetic
and much does not occur until we see it

any global impulse shattering is not seen

pulverisation process occur throughout the collapse

that energetic is taken from kinetic

no simulations using the accuracy of
for instance
sebastian and mcconnel's semiempirical finite element models
of steel, concrete, and composite structural elements
have been able to account such energetics and time-to-fall

it does not matter what mechanism of destruction is used
ultimately the fall time is purely an energetic calculation
a delta from initial to final state

that is why it is an interesting scientific mystery
to account for the collapse speed of the towers