explosieven gevonden in puin WTC-torens

[nadine]

Oorspronkelijk geplaatst door 2004gun

Doe uw onderzoek eens deftig, die post heb ik vorige week al eens gepost in een andere discussie (deze verschijn trouwens ook niet in Google search).

Sorry S

Don't be sorry
Want nu dat je beweert
1. dat die tekst van jezelf is en vertaald uit het Engels, dus door jezelf vertaald
2. dat je die ergens anders gepost hebt, maar natuurlijk geen informatie kunt/durft geven waar
3. en dat je wat hiervoor dit geschreven hebt als opmerking op een vraag waarom je de zin :

Oorspronkelijk geplaatst door 2004gun

Een groot deel werd gerecycleerd in Amerika door Metals Management, een bedrijf uit New York met aan het hoofd de Joodse directeur Alan Ratner.

gepost hebt

Oorspronkelijk geplaatst door Bristow

En nu moet jij eens uitleggen waarom de godsdienst van die Alan Ratner belangrijk is voor je argument.

je dan antwoordt:

Oorspronkelijk geplaatst door 2004gun

Was mij niet eens opgevallen, doet inderdaad momenteel niks ter zake

Dus het was je niet opgevallen wat zogezegd je eigen document bevat
betekent het ofwel:
a) dat je niet eens weet wat je zelf schrijft wanneer je een tekst vertaalt die zogezegd van jezelf komt,
b) ofwel de tekst toch gecopieerd hebt van strondfront.org
of wat eigenlijk de meest plausibele uitleg is dat
c) het je eigen tekst is die je op strondfront.org gepost hebt en niet goed opgelet hebt wanneer je die copieerde.

Nu voor iemand die zo door de mand valt, ben ik echt nieuwsgierig wat je nu gaat uitvinden?

[Gun]

Oorspronkelijk geplaatst door Knipp

één expert is op een leugen betrapt
===> alle experts missen credibiliteit

in dezelfde trant volstaat het 1 van jouw 1000 'feiten' te weerleggen om aan de 999 andere te moeten twijfelen

Deal ?

You've got a point ...

maar indien die zogenaamd ene expert de ganse Amerikaanse regering kan beet nemen (!?) (ook omdat ze wilden beet genomen worden aangaande dit onderwerp) zodat men deze informatie halstarrig tracht staande te houden voor de UNO, en niet zomaar een lokaal gazetje, bewijst ook dat diezelfde Amerikaanse overheid graag toehapt wanneer de informatie hen goed uitkomt, whether or not it is true.

Do we have a point too?

[Gun]

Oorspronkelijk geplaatst door Bristow

Het verhaal van de WMD van Saddam bewijst hoe weinig maakbaar de realiteit is.
Ten eerste, zelfs voor de oorlog waren er grote twijfels over de Amerikaanse beweringen. In de pers, zelfs de Amerikaanse pers, en in politieke middens, zelfs in de VS.
Ten tweede, vanuit de universiteiten kregen de beweringen van de administratie over de WMD geen steun.
Ten derde, na de oorlog, en heel snel eigenlijk, bleken de beweringen onhoudbaar.
Kijk hoe anders het zit met 9/11.
Dezelfde pers die zich al bijna twee jaar vrolijk maakt over de WMD beweringen gelooft wel degelijk dat Al Qaeda de aanslagen van 9/11 gepleegd heeft.
Ik wacht nog altijd.

is de oorlog eigenlijk al afgelopen?

U hebt een punt, die media stelde zich inderdaad kritischer op, maar we spreken hier ook over twee topics met een totaal ander gewicht.

Het pluimpje WMD in Irak wordt vergeleken met de grootste terroristische aanslag allertijden op een ongenaakbaar gewaande wereldmacht die hier nog nooit mee te maken had. Voor ons zit er misschien weinig verschil in, maar voor de Amerikaan ligt dat ff anders.
Komt erbij dat de Amerikaanse overheid in de publieke opinie intussen de link kon bewerkstelligen tussen beiden waardoor de media kon scoren bij de schaarse kritische Amerikaan door nu duidelijk wél hun kritische ingesteldheid te tonen. Alsof ze schoon schip wilden maken en de fouten van de afgelopen jaren konden corrigeren.

En anderzijds bewijst dit ook dat de ganse Amerikaanse regering graag 'wil beet genomen worden' en zich snel schaart achter twijfelachtige informatie die hen goed uitkomt, whether or not it is true.

[democratsteve]

Oorspronkelijk geplaatst door Bristow

Je bent "rond de pot aan het draaien", steve.
Op 13/9/2001 is er geen officieel verslag verschenen. Dat kan toch niet.
Het NIST is nu bezig met een heel uitvoerig wetenschappelijk onderzoek. Als je denkt dat al die wetenschappers en onderzoekers oneerlijk zijn, soit.
Maar vindt echte wetenschappers die de analyses van de NIST ontkrachten. En die dat doen met technische en wetenschappelijke argumenten.

Steeds maar verwijzen naar verklaringen en artikels van drie jaren geleden, dat "pakt niet".

Je bent rond de pot aan't draaien Steve.
Dat kan dat toch niet! bweu bweu bweu
ZOU JE NIET EENS EINDELIJK OPHOUDEN MET LULLEN!!!!!!!!!!!!
ZOU JE NIET EERST EENS ANTWOORDEN OP DE VRAGEN IN DE TWEE LANGE POSTS;
EN VOORAL. ZOU JE NIET EENS OPHOUDEN MET BESCHULDIGINGEN NAAR 'M HOOFD TE SLINGEREN DIE NERGEN OP SLAAN EN ZOU JE DAN ALS LAATSTE WILLEN OPHOUDEN MET ZELF LEUGENS TE VERTELLEN.

ALSTUBLIEFT!!!! VAN HUN EIGEN WEBSITE!!!!!!

Journal of Engineering Mechanics ASCE, in press
[SIZE=3]9/13/01[/SIZE], Expanded 9/22/01, Appendices 9/28/01)
Why Did the World Trade Center Collapse?—Simple Analysis
By Zdenek P. Bazant1, Fellow ASCE, and Yong Zhou2

Abstract: This paper3 presents a simplified approximate analysis of the overall collapse of the towers of World Trade Center in New York on September 11, 2001. The analysis shows that if prolonged heating caused the majority of columns of a single floor to lose their load carrying capacity, the whole tower was doomed. The structural resistance is found to be an order of magnitude less than necessary for survival, even though the most optimistic simplifying assumptions are introduced.

Introduction and Failure Scenario
The 110-story towers of the World Trade Center were designed to withstand as a whole the forces caused by a horizontal impact of a large commercial aircraft (Appendix I). So why did a total collapse occur? The cause was the dynamic consequence of the prolonged heating of the steel columns to very high temperature. The heating lowered the yield strength and caused viscoplastic (creep) buckling of the columns of the framed tube along the perimeter of the tower and of the columns in the building core. The likely scenario of failure is approximately as follows.

In stage 1 (Fig. 1), the conflagration caused by the aircraft fuel spilled into the structure causes the steel of the columns to be exposed to sustained temperatures apparently exceeding 800°C. This assumption is crucial to the entire analysis, and there is no basis for it. Actual tests of uninsulated steel structures exposed to gas and diesel fuel for sustained periods never exceeded 360°C. And widespread flames were no longer visible in either tower when it collapsed, only dark smoke. The heating is probably accelerated by a loss of the protective thermal insulation of steel during the initial blast. Blast? By implying that the impact fireballs were blasts, the authors confuse explosions, which produce very high pressures, with fireballs, which don't. A detonation wave can be generated by the sudden ignition of an unburned hydrocarbon-air mixture, but is not produced when ignition is continuous, as appeared to be the case with the dispersing fuel in the jet impacts. The fireballs took about two seconds to expand. Had they detonated, they would have appeared in milliseconds. At such temperatures, structural steel suffers a decrease of yield strength and exhibits significant viscoplastic deformation (i.e., creep—an increase of deformation under sustained load). This leads to creep buckling of columns (e.g., Bazant and Cedolin 1991, Sec. 9), which consequently lose their load carrying capacity (stage 2). Once more than about a half of the columns in the critical floor that is heated most suffer buckling (stage 3), the weight of the upper part of the structure above this floor can no longer be supported, and so the upper part starts falling down onto the lower part below the critical floor, gathering speed until it impacts the lower part. This flies in the face of engineering practice, which makes things at least four times as strong as they would have to be to sustain maximum anticipated loads. Actual load conditions were a fraction of those anticipated loads, since it was not a windy day, and the floors above the impacts were holding only a fraction of their rated capacities. So 90% would be a more realistic estimate of the needed column failure rate. At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity. The vertical impact of the mass of the upper part onto the lower part (stage 4) applies enormous vertical dynamic load on the underlying structure, far exceeding its load capacity, even if it is not heated. This causes failure of an underlying multi-floor segment of the tower (stage 4), in which the failure of the connections of the floor-carrying trusses to the columns is either accompanied or quickly followed by buckling of the core columns and overall buckling of the framed tube, was it too fast to see on the videos, or was it behind the dust? with the buckles probably spanning the height of many floors (stage 5, at right), and the upper part possibly getting wedged inside an emptied lower part of the framed tube (stage 5, at left). The buckling is initially plastic but quickly leads to fracture in the plastic hinges. When will they learn to use metal instead of plastic hinges!? The part of building lying beneath is then impacted again by an even larger mass falling with a greater velocity, and the series of impacts and failures then proceeds all the way down (stage 5).

Elastic Dynamic Plastic Fantastic Analysis
The details of the failure process after the decisive initial trigger that sets the upper part in motion are of course very complicated and their clarification would require large computer simulations. For example, the upper part of one tower is tilting as it begins to fall (see Appendix II); the distribution of impact forces among the underlying columns of the framed tube and the core, and between the columns and the floor-supporting trusses, is highly nonuniform; etc. However, a computer is not necessary to conclude that the collapse of the majority of columns of one floor must have caused the whole tower to collapse. This may be demonstrated by the following elementary calculations, in which simplifying assumptions most optimistic in regard to survival are made. That's a preposterous claim, since it's not even clear that elastic dynamic analysis, whatever it is, is even remotely applicable.

For a short time after the vertical impact of the upper part, but after the elastic wave generated by the vertical impact has propagated to the ground, the lower part of the structure can be approximately considered to act as an elastic spring (Fig. 2a). What is its stiffness C? It can vary greatly with the distribution of the impact forces among the framed tube columns, between these columns and those in the core, and between the columns and the trusses supporting concrete floor slabs.

For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally. Unlikely though such a distribution may be, it is nevertheless the most optimistic hypothesis to make because the resistance of the building to the impact is, for such a distribution, the highest. If the building is found to fail under a uniform distribution of the impact forces, it would fail under any other distribution. They cleverly insert the idea of uniform symmetric collapse -- one of the most obvious problems with the gravity-collapse -- as an optimistic hypothesis. According to this hypothesis, one may estimate that C 71 GN/m (due to unavailability of precise data, an approximate design of column cross sections had to be carried out for this purpose).

The downward displacement from the initial equilibrium position to the point of maximum deflection of the lower part (considered to behave elastically) is h + (P/C) where P = maximum force applied by the upper part on the lower part and h = height of critical floor columns (= height of the initial fall of the upper part) 3.7 m. The energy dissipation, particularly that due to the inelastic deformation of columns during the initial drop of the upper part, may be neglected, i.e., the upper part may be assumed to move through distance h almost in a free fall (indeed, the energy dissipated in the columns during the fall is at most equal to 2πX the yield moment of columns, X the number of columns, which is found to be only about 12% of the gravitational potential energy release if the columns were cold, and much less than that at 800°C). What is the the yield moment of the columns, and how many columns are there? The confidence of the authors in their conclusions is strinking, given the lack of any clear details of the tower's structures. Well, this 12% isn't the only thing we have to take their word for. So the loss of the gravitational potential energy of the upper part may be approximately equated to the strain energy of the lower part at maximum elastic deflection. This gives the equation mg[h + (P/C)] = P2/2C in which m = mass of the upper part (of North Tower) 58·106 kg, and g = gravity acceleration. The solution P = Pdyn yields the following elastically calculated overload ratio due to impact of the upper part:



where P0 = mg = design load capacity. In spite of the approximate nature of this analysis, it is obvious that the elastically calculated forces in columns caused by the vertical impact of the upper part must have exceeded the load capacity of the lower part by at least an order of magnitude.

Another estimate, which gives the initial overload ratio that exists only for a small fraction of a second at the moment of impact, is



where A = cross section area of building, Eef= cross section stiffness of all columns divided by A, ρ = specific mass of building per unit volume. This estimate is calculated from the elastic wave equation which yields the intensity of the step front of the downward pressure wave caused by the impact if the velocity of the upper part at the moment of impact on the critical floor is considered as the boundary condition (e.g., Bazant and Cedolin, Sec. 13.1). After the wave propagates to the ground, the former estimate is appropriate.

An important hypothesis implied in this analysis is that the impacting upper part, many floors in height, is so stiff that it does not bend nor shear on vertical planes, and that the distribution of column displacements across the tower is almost linear, like for a rigid body. If, however, the upper part spanned only a few floors (say, 3 to 6), then it could be so flexible that different column groups of the upper part could move down separately at different times, producing a series of small impacts that would not be fatal (in theory, if people could have escaped from the upper part of the tower, the bottom part of the tower could have been saved if the upper part were bombed, exploded or weakened by some "smart" structure mechanism to collapse onto the lower part gradually as a pile of rubble, instead of impacting it instantly as an almost rigid body). Just what we need! Smart-collapsing buildings. You many want to wear a hardhat if you go to work in one of these buildings because that falling rubble can hurt!

Analysis of Inelastic Energy Dissipation Ideation
The inelastic deformation of the steel of the towers involves plasticity and fracture. Since we are not attempting to model the details of the real failure mechanism but seek only to prove that the towers must have collapsed and do so in the way seen (Engineering 2001, American 2001), we will here neglect fracture, even though the development of fractures is clearly discerned in the photographs of the collapse. I see a lot of fractured steel but no sign of fractures developing -- just a progression of explosions down the building fracturing the frame along the way. Assuming the steel to behave plastically, with unlimited ductility, we are making the most optimistic assumption with regard to the survival capacity of the towers (in reality, the plastic hinges, especially the hinges at column connections, must have fractured, and done so at relatively small rotation, causing the load capacity to drop drastically).

The basic question to answer is: Can the fall of the upper part be arrested by energy dissipation during plastic buckling which follows the initial elastic deformation? Many plastic failure mechanisms could be considered, for example: (a) the columns of the underlying floor buckle locally (Fig. 1, stage 2); (b) the floor-supporting trusses are sheared off at the connections to the framed tube and the core columns and fall down within the tube, depriving the core columns and the framed tube of lateral support, and thus promoting buckling of the core columns and the framed tube under vertical compression (Fig. 1, stage 4, Fig. 2c); and how long would those massive core columns remain standing after losing the lateral support of the perimeter wall? I think more than the one second they did. or (c) the upper part is partly wedged within the emptied framed tube of the lower part, pushing the walls of the framed tube apart (Fig. 1, stage 5). That would keep the cores of the falling and intact portions aligned, so the core columns would have been crushing themselves as they went down. Although each of these mechanism can be shown to lead to total collapse, (I wish I were as smart as these guys so I could see too.) a combination of the last two seems more realistic (the reason: multi-story pieces of the framed tube, with nearly straight boundaries apparently corresponding to plastic hinge lines causing buckles on the framed tube wall, were photographed falling down; see, e.g., Engineering 2001, American 2001).

Regardless of the precise failure mode, experience with buckling indicates that the while many elastic buckles simultaneously coexist in an axially compressed tube, the plastic deformation localizes (because of plastic bifurcation) into a single buckle at a time (Fig. 1, stage 4; Fig. 2c), and so the buckles must fold one after another. Thus, at least one plastic hinge, and no more than four plastic hinges, per column line are needed to operate simultaneously in order to allow the upper part to continue moving down (Fig. 2b, Bazant and Cedolin 1991) (this is also true if the columns of only one floor are buckling at a time). At the end, the sum of the rotation angles θi (i = 1, 2, . . ) of the hinges on one column line, Σθi, cannot exceed 2π (Fig. 2b). This upper-bound value, which is independent of the number of floors spanned by the buckle, is used in the present calculations since, in regard to survival, it represents the most optimistic hypothesis, maximizing the plastic energy dissipation.

Calculating the dissipation per column line of the framed tube as the plastic bending moment Mp of one column (Jirasek and Bazant 2002), times the combined rotation angle θi = 2π (Fig. 2b), and multiplying this by the number of columns, one concludes that the plastically dissipated energy Wp is, optimistically, of the order of 0.5 GN m (for lack of information, certain details such as the wall thickness of steel columns, were estimated by carrying out approximate design calculations for this building).

To attain the combined rotation angle Σθi = 2π of the plastic hinges on each column line, the upper part of the building must move down by the additional distance of one buckle, which is at least one floor below the floor where the collapse started. So the additional release of gravitational potential energy Wg ≥ mg · 2h 2 X 2:1 GN m = 4.2 GN m. To arrest the fall, the kinetic energy of the upper part, which is equal to the potential energy release for a fall through the height of at least two floors, would have to be absorbed by the plastic hinge rotations of one buckle, i.e., Wg=Wp would have to be less than 1. Rather,



if the energy dissipated by the columns of the critical heated floor is neglected. If the first buckle spans over n floors (3 to 10 seems likely), this ratio is about n times larger. So, even under by far the most optimistic assumptions, the plastic deformation can dissipate only a small part of the kinetic energy acquired by the upper part of building.

When the next buckle with its group of plastic hinges forms, the upper part has already traveled many floors down and has acquired a much higher kinetic energy; the percentage of the kinetic energy dissipated plastically is then of the order of 1%. This claim is probably ridiculous, but in any case I can't find an argument that the elastic dynamic analysis and its plastic hinges applies even remotely to those structures. The percentage continues to decrease further as the upper part moves down. If fracturing in the plastic hinges were considered, a still smaller (in fact much smaller) energy dissipation would be obtained. So the collapse of the tower must be an almost free fall. This conclusion is supported by the observation that the duration of the collapse of the tower, observed to be 9 s, was about the same as the duration of a free fall in a vacuum from the tower top (416 m above ground) to the top of the final heap of debris (about 25 m above ground), which is It further follows that the brunt of vertical impact must have gone directly into the columns of the framed tube and the core and that any delay Δt of the front of collapse of the framed tube behind the front of collapsing (‘pancaking’) floors must have been negligible, or else the duration of the total collapse of the tower, 9 s + Δt, would have been significantly longer than 9 s. However, even for a short delay Δt, the floors should have acted like a piston running down through an empty tube, which helps to explain the smoke and debris that was seen being expelled laterally from the collapsing tower. Huh? Is this supposed to explain how the towers' tops crushed a 1000-foot high pillar of resilient steel as if there was only air there?

Problems of Disaster Mitigation and Design
Designing tall buildings to withstand this sort of attack seems next to impossible. If by "this sort of attack" they mean explosive demolition, I would agree. It would require a much thicker insulation of steel, with blast-resistant protective cover. No, that's useless, because they could cut away the protective cover when they place the explosives. Replacing the rectangular framed tube by a hardened circular monolithic tube with tiny windows might help to deflect much of the debris and fuel from an impacting aircraft sideways, but regardless of cost, who would want to work in such a building? I think most people would settle for a collapse-proof building.

The problems appear to be equally severe for concrete columns because concrete heated to such temperatures undergoes explosive thermal spalling, thermal fracture and disintegration due to dehydration of hardened cement paste (e.g., Bazant and Kaplan 1996). These questions arise not only for buildings supported on many columns but also for the recent designs of tall buildings with a massive monolithic concrete core functioning as a tubular mast. These recent designs use high-strength concrete which, however, is even more susceptible to explosive thermal spalling and thermal fracture than normal concrete. The use of refractory concretes as the structural material invites many open questions (Bazant and Kaplan 1996). Special alloys or various refractory ceramic composites may of course function at such temperatures, but the cost would increase astronomically. It will nevertheless be appropriate to initiate research on materials and designs that would postpone the collapse of the building so as to extend the time available for evacuation, because even though multi-story steel structures have never "collapsed" before 9-11, now their collapse will be inevitable in the event of fire. provide a hardened and better insulated stairwell, or even prevent collapse in the case of a less severe attack such as an off-center impact or the impact of an aircraft containing little fuel. Lessons should be drawn for improving the safety of building design in the case of lesser disasters. For instance, in view of the progressive dynamic collapse of a stack of all the floors of the Ronan Point apartments in the U.K., caused by a gas explosion in one upper floor (Levy and Salvadori 1992), the following design principle, determining the appropriate ff of redundancy, should be adopted: If only a certain judiciously specified minority of the columns or column-floor connections at one floor are removed, the mass that might fall down from the superior structure must be so small that its impact on the underlying structure would not cause dynamic overload.

Closing Comments
Once accurate computer calculations are carried out, various details of the failure mechanism will doubtless be found to differ from the present simplifying hypotheses. Errors by a factor of 2 would not be terribly surprising, but that would hardly matter since the present analysis reveals order-of-magnitude differences between the dynamic loads and the structural resistance. There have been many interesting, but intuitive, competing explanations of the collapse. Theorists were very busy between September 11th and 13th! To decide their viability, however, it is important to do at least some crude calculations. For example, it has been suggested that the connections of the floor-supporting trusses to the framed tube columns were not strong enough. Maybe they were not, but even if they were it would have made no difference, as shown by the present simple analysis.

But stay tuned, because once that 800 Cº figure in this paper gets noticed, the trusses and their connectors will be heavily relied on in a more fine-tuned official explanation.
The main purpose of the present analysis is to prove that the whole tower must have collapsed if the fire destroyed the load capacity of the majority of columns of a single floor. This purpose justifies the optimistic simplifying assumptions regarding survival made at the outset, which include unlimited plastic ductility (i.e., absence of fracture), uniform distribution of impact forces among the columns, disregard of various complicating details (e.g., the possibility that the failures of floor-column connections and of core columns preceded the column and tube failure, or that the upper tube got wedged inside the lower tube), etc. If the tower is found to fail under these very optimistic assumptions, it will certainly be found to fail when all the detailed mechanisms are analyzed, especially since there are order-of-magnitude differences between the dynamic loads and the structural resistance.

An important puzzle at the moment is why the adjacent 46-story building, into which no significant amount of aircraft fuel could have been injected, collapsed as well. Despite the lack of data at present, the likely explanation seems to be that high temperatures (though possibly well below 800°C) persisted on at least one floor of that building for a much longer time than specified by the current fire code provisions.

Appendix I. Elastic Dynamic Response to Aircraft Impact
A simple estimate based on the preservation of the combined momentum of the impacting Boeing 767-200 ( 179,000 kg X 550 km/h) and the momentum of the equivalent mass Meq of the interacting upper part of the tower ( 141 ·106 X v0 ) indicates that the initial average velocity v0 imparted to the upper part of the tower was only about 0.7 km/h = 0.19 m/s. Mass Meq, which is imagined as a concentrated mass mounted at the height of the impacted floor on a massless free-standing cantilever with the same bending stiffness as the tower (Fig. 2d), has been calculated from the condition that its free vibration period be equal to the first vibration period of the tower, which has been roughly estimated as T1 = 14 s (Meq 44% of the mass of the whole tower). The dynamic response after impact may be assumed to be dominated by the first free vibration mode, of period T1. Therefore, the maximum horizontal deflection w0 = v0Ti/2π 0.4 m, which is well within the design range of wind-induced elastic deflections. So it is not surprising that the aircraft impact per se damaged the tower only locally.

The World Trade Center was designed for an impact of Boeing 707-320 rather than Boeing 767-320. But note that the maximum takeoff weight of that older, less effcient, aircraft is only 15% less than that of Boeing 767-200. Besides, the maximum fuel tank capacity of that aircraft is only 4% less. These differences are well within the safety margins of design. So the observed response of the towers proves the correctness of the original dynamic design. What was not considered in design was the temperature that can develop in the ensuing fire. Here the lulling experience from 1945 might have been deceptive; that year, a two-engine bomber (B-25), flying in low clouds to Newark at about 400 km/h, hit the Empire State Building (381 m tall, built in 1932) at the 79th floor (278 m above ground)—the steel columns (much heavier than in modern buildings) suffered no significant damage, and the fire remained confined essentially to two floors only (Levy and Salvadori 1992).

Appendix II. Why Didn’t the Upper Part Pivot About Its Base?
Since the top part of the South Tower tilted (Fig. 3a), many people wonder: Why didn’t the upper part of the tower fall to the side like a tree, pivoting about the center of the critical floor? Before wading into the following mumbo-jumbo it's worth noting that once the top of the tower started its vertical plunge, its rate of rotation slowed down. This can only be explained by the breakup of the top (the piston used above to "explain" the near free-fall rate of destruction) which would have destroyed its moment of inertia. (Fig. 3b) To demonstrate why, and thus to justify our previous neglect of tilting, is an elementary exercise in dynamics. Assume the center of the floor at the base of the upper part (Fig. 3b) to move for a while neither laterally nor vertically, i.e., act as a fixed pivot. Equating the kinetic energy of the upper part rotating as a rigid body about the pivot at its base (Fig. 3c) to the loss of the gravitational potential energy of that part (which is here simpler than using the Lagrange equations of motion), we have where x is the vertical coordinate (Fig. 3c). 5 This provides



where θ = rotation angle of the upper part, H1 = its height, and the superposed dots denote time derivatives (Fig. 3c). Considering the dynamic equilibrium of the upper part as a free body, acted upon by distributed inertia forces and a reaction with horizontal component F at base (Fig. 3d), one obtains . Evidently, the maximum horizontal reaction during pivoting occurs for θ = 45°, and so



where, for the upper part of South Tower, m 87 · 106 kg.

Could the combined plastic shear resistance Fp of the columns of one floor (Fig. 3f) sustain this horizontal reaction? For plastic shear, there would be yield hinges on top and bottom of each resisting column; Fig. 3e (again, aiming only at an optimistic upper bound on resistance, we neglect fracture). The moment equilibrium condition for the column as a free body shows that each column can at most sustain the shear force F1 = 2Mp/h1 where h1 2:5 m = effective height of column, and Mp 0:3 MN m = estimated yield bending moment of one column, if cold. Assuming that the resisting columns are only those at the sides of the framed tube normal to the axis of rotation, which number about 130, we get Fp 130F1 31 MN. So, the maximum horizontal reaction to pivoting would cause the overload ratio



if the resisting columns were cold. Since they are hot, the horizontal reaction to pivoting would exceed the shear capacity of the heated floor still much more (and far more if fracture were considered).

Since F is proportional to sin 2θ, its value becomes equal to the plastic limit when sin 2θ = 1/10.3. From this we further conclude that the reaction at the base of the upper part of South Tower must have begun shearing the columns plastically already at the inclination



The pivoting of the upper part must have started by an asymmetric failure of the columns on one side of building, but already at this very small angle the dynamic horizontal reaction at the base of the upper part must have reduced the vertical load capacity of the remaining columns of the critical floor (even if those were not heated). That must have started the downward motion of the top part of the South Tower, and afterwards its motion must have become predominantly vertical. Hence, a vertical impact of the upper part onto the lower part must have been the dominant mechanism.

Finally note that the horizontal reaction Fmax is proportional to the weight of the pivoting part. Therefore, if a pivoting motion about the center of some lower floor were considered, Fmax would be still larger.

Appendix III. Plastic Load-Shortening Diagram of Columns
Normal design deals only with initial bifurcation and small deflections, in which the diagram of load versus axial shortening of an elasto-plastic column exhibits hardening rather than softening. However, the columns of the towers suffered very large plastic deflections, for which this diagram exhibits pronounced softening. Fig. 5 shows this diagram as estimated for these towers. The diagram begins with axial shortening due to plastic yielding at load P10 = A1fi where A1 = crosssection area of one column and fy = yield limit of steel. At the axial shortening of about 3%, there is a plastic bifurcation (if imperfections are ignored). After that, undeflected states are unstable and three plastic hinges (Fig. 5) must form (if we assume, optimistically, the ends to be fixed). From 6 the condition of moment equilibrium of the half-column as a free body (Fig. 5), the axial load then is P1 = 4Mp/L sinθ, while, from the buckling geometry, the axial shortening is u = L(1 - cosθ), where L = distance between the end hinges. Eliminating plastic hinge rotation θ, we find that the plastic load-shortening diagram (including the pre- and post-bifurcation states) is given by



which defines the curve plotted in Fig. 5. This curve is an optimistic upper bound since, in reality, the plastic hinges develop fracture (e.g., Bazant and Planas 1998), and probably do so already at rather small rotations. The area under this curve represents the dissipated energy.

If it is assumed that one or several floor slabs above the critical heated floor collapsed first, then the L to be substituted in (8) is much longer than the height of columns of one floor. Consequently, P1(u) becomes much smaller (and the Euler elastic critical load for buckling may even become less than the plastic load capacity, which is far from true when L is the column height of a single floor).

It has been suggested that the inelastic deformation of columns might have ‘cushioned’ the initial descent of the upper part, making it almost static. However, this is impossible because, for gravity loading, a softening of the load-deflection diagram (Fig. 5) always causes instability and precludes static deformation (Bazant and Cedolin 1991, Chpt. 10 and 13). The downward acceleration of the upper part is ü = N[P10 - P1(u)]/m where N = number of columns and, necessarily, P10 = mg/N. This represents a differential equation for u as a function of time t, and its integration shows that the time that the upper part takes to fall through the height of one story is, for cold columns, only about 6% longer than the duration of a free fall from that height, which is 0.87 s. For hot columns, the difference is of course much less than 6%. So there is hardly any ‘cushioning’.

[nadine]

Zeg eens weedman, voor je iets post waar je niet veel van verstaat, ben je al gaan zoeken wat er later in dat "journal" staat? Het zou mij zeker niet verwonderen, met dit type publucaties gewerkt te hebben, dat je later tegengestelde artikelen vindt! En alles hirein berust op één hypothese van temperatuur in gans andere condities waargenomen. Het artikel zwijgt over warmtegeleiding en accumulatie dat ze zweten

Wat mij wel opvalt bij jou is dat sinds ik op de andere thread dit gevraagd hebt

Oorspronkelijk geplaatst door nadine

Wel, geef eens het telefoonnummer van die Redyke van Protec. Zal hem zelf eens laten opbellen door iemand met kennis en niet met weed en dan ben ik ook bereid dergelijk uitlatingen, indien hij dit doet hier te bevestigen.

Je mag het ook per PB zenden, maar anders zal ik het zelf ook wel vinden als je nu ineens ermee een probleem krijgt. Capito?

je daar niet meer durft opkomen. Het zal dus wel duidelijk zijn voor iedereen dat je daar dus uit je nek hebt zitten lullen en nooit met die Redyke van Protec gesproken hebt. Misschien bestaat die vent niet eens en heb je dat ook in een of andere weedsessie gehallucineerd....

[Bristow]

Oorspronkelijk geplaatst door democratsteve

Je bent rond de pot aan't draaien Steve.
Dat kan dat toch niet! bweu bweu bweu
ZOU JE NIET EENS EINDELIJK OPHOUDEN MET LULLEN!!!!!!!!!!!!
ZOU JE NIET EERST EENS ANTWOORDEN OP DE VRAGEN IN DE TWEE LANGE POSTS;
EN VOORAL. ZOU JE NIET EENS OPHOUDEN MET BESCHULDIGINGEN NAAR 'M HOOFD TE SLINGEREN DIE NERGEN OP SLAAN EN ZOU JE DAN ALS LAATSTE WILLEN OPHOUDEN MET ZELF LEUGENS TE VERTELLEN.

ALSTUBLIEFT!!!! VAN HUN EIGEN WEBSITE!!!!!!

Journal of Engineering Mechanics ASCE, in press
[size=3]9/13/01[/size], Expanded 9/22/01, Appendices 9/28/01)
Why Did the World Trade Center Collapse?—Simple Analysis
By Zdenek P. Bazant1, Fellow ASCE, and Yong Zhou2

Steve, je merkt het misschien niet, maar je bevestigt alléén wat ik al enkele keren geschreven heb. (En je moet nier roepen, ik hoor je ook wel met kleine letters.)

Je blijft maar verwijzen naar berichten uit de eerste weken na 9/11.

Hoe officieel is een artikel dat op 13/9/2001 wordt gepubliceerd ?
Hoe gefundeerd is een analyse die 13/9/2001 wordt gepubliceerd ?
Daarom dat ze het artikel (geen officieël verslag) een "simple analysis" noemen.

Het is een poging, twee dagen na de aanslag, om te proberen te begrijpen wat er gebeurd is. Verdienstelijk, maar, zoals ze het zelf zeggen, "a simplified approximate analysis".

De officiële verslagen, de gefundeerde wetenschappelijke analyses zijn natuurlijk veel later gekomen, en zijn nog niet eens af.
Als je wist wat wetenschappelijk onderzoek inhoudt dan zou je dat zonder meer begrijpen.

Daar verwijs ik naar, niet naar artikels van 13/9/2001, die jij dan promoveert tot officiële onderzoeken.

[exodus]

Oorspronkelijk geplaatst door Bristow

Steve, je merkt het misschien niet, maar je bevestigt alléén wat ik al enkele keren geschreven heb. (En je moet nier roepen, ik hoor je ook wel met kleine letters.)

Je blijft maar verwijzen naar berichten uit de eerste weken na 9/11.

Waarom zouden die berichten minder relevant zijn?? ALs men iets bestudeert dan moet men naar het alles kijken. Juist die berichten kunnen zeer interessant zijn, vooral als men uitgaat van inside job, want dan heeft men nog geen tijd om een "cover-up" te doen.

[exodus]

Oorspronkelijk geplaatst door Bristow

Zoals Herr Flick (post 240) al heeft opgemerkt zou dat een wel heel omslachtige manier zijn geweest om die 10/15 mensen te vermoorden.

Maar ik denk dat het hier dieper gaat.

De believers bouwen enerzijds op de echte of vermeende ongerijmdheden in de officiële versie. Fair enough.

Ze wijzen heel terecht op allerlei verklaringen van officiële instanties die kant noch wal raken. Ze zien hierin dan bewijzen dat er "iets" achter zit.
En ze hebben nog gelijk ook. Wat er (m.i.) meestal achter zit is een dysfunctie van de regering, flaters bijvoorbeeld, of verkeerde prioriteiten.

Een andere pijler van de believers zijn de "toevalligheden". En hier slaan ze de bal meestal mis.

Weet je, bij 9/11 zijn er dan wel een heel aantal "toevalligheden". Ik denk dat de non-believers liever in "toevalligheidstheoriëen" geloven.... Kom zeg, als je het allemaal moet verklaren met flaters en toevalligheden dat is gewoonweg niet doenbaar en niet consistent.

Over die flaters... dat is juist wat de Amerikaanse regering je wil doen geloven. Het zijn zogezegd allemaal flaters. De realiteit is wel enigzins anders, achter die facade van flaters gaat wel iets anders schuil.

Durf jij de war games van NORAD op 9/11 een toevalligheid noemen???

[Bristow]

Oorspronkelijk geplaatst door exodus

Waarom zouden die berichten minder relevant zijn?? ALs men iets bestudeert dan moet men naar het alles kijken. Juist die berichten kunnen zeer interessant zijn, vooral als men uitgaat van inside job, want dan heeft men nog geen tijd om een "cover-up" te doen.

Waarom heeft men geen tijd gehad voor de "cover-up"?

Dit werd volgens jullie theorieën jaren van tevoren gepland.
Aan de "cover-up" hebben ze dan niet gedacht?

Maar nogmaals, u probeert de officiële versie over WTC 1/2 te ontkrachten door te verwijzen naar een artikel van 13/9/01. Dit artikel is niet de officiële versie, dit artikel is niet een wetenschappelijk onderzoek. Twee dagen na de aanslag, get real zeg !

Al uw argumenten die op dat artikel gebouwd zijn daarom inderdaad totaal irrelevant.

[Bristow]

Oorspronkelijk geplaatst door exodus

Durf jij de war games van NORAD op 9/11 een toevalligheid noemen???

War game, beste exodus, de s is er teveel aan.

Er was welgeteld één wargame van NORAD op die dag (en eigenlijk de hele week ervoor). De rest van de wargames zjn verzinsels zonder énig bewijs.

De "toevallen" waar je naar verwijst, daar hebben we al op geantwoord.

[exodus]

Het zijn zogezegd allemaal toevallen en flaters. Dat is hoe de non-believers 9/11 verklaren.. Ze denken natuurlijk dat de believers het serieus mis hebben en te veel fantasie hebben.

Hieronder een interview met een voormalige Duitse minister. In de jaren 80 onderzocht hij geheime diensten zoals Stasi en KGB, hij is een kenner op het gebied van inlichtingendiensten.

Lees eens wat die man zegt. Is hij ook een fantast die het toaal mis heeft??

[font=Arial]Interview with former German Defense Minister Von Buelow[/font]

[font=Arial][/font]

[font=Arial](DRAFT) [Source: Tagesspiegel, Jan. 13] PARTIAL TRANSLATION[/font]

[font=Arial]{The following interview with Von Buelow appeared in the German
daily }Tagesspiegel,{ on Jan. 13.}[/font]

[font=Arial]Q: You seem so angry, really upset.[/font]

[font=Arial]Von Buelow: I can explain what's bothering me: I see that
after the horrifying attacks of Sept. 11, all political public
opinion is being forced into a direction that I consider wrong.[/font]

[font=Arial]Q: What do you mean by that?[/font]

[font=Arial]Von Buelow: I wonder why many questions are not asked.
Normally, with such a terrible thing, various leads and tracks
appear that are then commented on, by the investigators,
the media, the government: Is there something here or not?
Are the explanations plausible? This time, this is not the case
at all. It already began just hours after the attacks
in New York and Washington and--[/font]

[font=Arial]Q: In those hours, there was horror, and grief.[/font]

[font=Arial]Von Buelow: Right, but actually it was astounding:
There are 26 intelligence services in the U.S.A.
with a budget of $30 billion--[/font]

[font=Arial]Q: More than the German defense budget.[/font]

[font=Arial]Von Buelow: --which were not able to prevent the attacks.
In fact, they didn't even have an inkling they would happen.
For 60 decisive minutes, the military and intelligence agencies
let the fighter planes stay on the ground, 48 hours later,
however, the FBI presented a list of suicide attackers.
Within ten days, it emerged that seven of them were still alive.[/font]

[font=Arial]Q: What, please?[/font]

[font=Arial]Von Buelow: Yes, yes. And why did the FBI chief take no position
regarding contradictions? Where the list came from,
why it was false? If I were the chief investigator
(state attorney) in such a case,
I would regularly go to the public, and give information
on which leads are valid and which not.[/font]

[font=Arial]Q: The U.S. government talked about an emergency situation
after the attacks: They said they were in a war.
Is it not understandable that one does not tell the enemy
everything one knows about him?[/font]

[font=Arial]Von Buelow: Naturally. But a government which goes to war,
must first establish who the attacker, the enemy, is.
It has a duty to provide evidence.
According to its own admission,
it has not been able to present any evidence
that would hold up in court.[/font]

[font=Arial]Q: Some information on the perpetrators has been proven
with documents. The suspected leader, Mohammad Atta,
left Portland for Boston on the morning of Sept. 11,
in order to board the plane that later hit the World Trade Center[/font]

[font=Arial]Von Buelow: If this Atta was the decisive man in the operation,
it's really strange that he took such a risk of taking a plane
that would reach Boston such a short time before
the connecting flight. Had his flight been a few minutes late,
he would not have been in the plane that was hijacked.
Why should a sophisticated terrorist do this?
One can, by the way, read on CNN (Internet)
that none of these names were on the official passenger lists.
None of them had gone through the check-in procedures.
And why did none of the threatened pilots
give the agreed-upon code 7700 over the [Steuerknueppel: STEERING NOB?] to the ground station?
In addition: The black boxes which are fire and shock proof,
as well as the voice recordings, contain no valuable data--[/font]

[font=Arial]Q: That sounds like--[/font]

[font=Arial]Von Buelow: --like assailants who, in their preparations,
leave tracks behind them like a herd of stampeding elephants?
They made payments with credit cards with their own names;
they reported to their flight instructors with their own names.
They left behind rented cars with flight manuals in Arabic
for jumbo jets. They took with them, on their suicide trip,
wills and farewell letters, which fall into the hands of the FBI,
because they were stored in the wrong place
and wrongly addressed. Clues were left like behind
like in a child's game of hide-and-seek,
which were to be followed![/font]

[font=Arial]There is also the theory of one British flight engineer:[/font]

[font=Arial]According to this, the steering of the planes
was perhaps taken out of the pilots' hands, from outside.[/font]

[font=Arial]The Americans had developed a method in the 1970s,
whereby they could rescue hijacked planes
by intervening into the computer piloting
[automatic pilot system]. This theory says,
this technique was abused in this case. That's a theory....[/font]

[font=Arial]Q: Which sounds really adventurous, and was never considered.[/font]

[font=Arial]Von Buelow: You see! I do not accept this theory,
but I find it worth considering. And what about
the obscure stock transactions?
In the week prior to the attacks,
the amount of transactions in stocks in American Airlines,
United Airlines, and insurance companies, increased 1,200%.
It was for a value of $15 billion.
Some people must have known something. Who?[/font]

[font=Arial]Q: Why don't you speculate on who it might have been.[/font]

[font=Arial]Von Buelow: With the help of the horrifying attacks,
the Western mass democracies were subjected to brainwashing.
The enemy image of anti-communism doesn't work any more;
it is to be replaced by peoples of Islamic belief.
They are accused of having given birth to suicidal terrorism.[/font]

[font=Arial]Q: Brainwashing? That's a tough term.[/font]

[font=Arial]Von Buelow: Yes? But the idea of the enemy image doesn't
come from me. It comes from Zbigniew Brzezinski and Samuel
Huntington, two policy-makers of American intelligence
and foreign policy. Already in the middle of he 1990s,
Huntingon believed, people in Europe and the U.S.
needed someone they could hate--
this would strengthen their identification
with their own society. And Brzezinski, the mad dog,
as adviser to President Jimmy Carter,
campaigned for the exclusive right of the U.S.
to seize all the raw materials of the world,
especially oil and gas.[/font]

[font=Arial]Q: You mean, the events of Sept. 11--[/font]

[font=Arial]Von Buelow: --fit perfectly in the concept
of the armaments industry, the intelligence agencies,
the whole military-industrial-academic complex. This is in fact
conspicuous. The huge raw materials reserves of the former Soviet
Union are now at their disposal, also the pipeline routes and--[/font]

[font=Arial]Q: Erich Follach described that at length in {Spiegel}:
``It's a matter of military bases, drugs, oil and gas reserves.''[/font]

[font=Arial]Von Buelow: I can state: the planning of the attacks
was technically and organizationally a master achievement.
To hijack four huge airplanes within a few minutes
and within one hour, to drive them into their targets,
with complicated flight maneuvers!
This is unthinkable, without years-long support
from secretapparatuses of the state and industry.[/font]

[font=Arial]Q: You are a conspiracy theorist![/font]

[font=Arial]Von Buelow: Yeah, yeah. That's the ridicule heaped
[on those raising these questions] by those who would prefer
to follow the official, politically correct line.
Even investigative journalists are fed propaganda
and disinformation. Anyone who doubts that,
doesn't have all his marbles! That is your accusation.[/font]

[font=Arial]Q: Your career actually speaks against the idea
that you are not in your right mind.
You were already in the 1970s, state secretary
in the Defense Ministry; in 1993 you were the SPD
[Social Democratic Party] speaker
in the Schalk-Golodkowski investigation committee--[/font]

[font=Arial]Von Buelow: And it all began there!
Until that time, I did not have any great knowledge
of the work of intelligence agencies.
And now we had to take note of a great discrepancy:
We shed light on the dealings of the Stasi
and other East bloc intelligence agencies
in the field of economic criminality,
but as soon as we wanted to know something
about the activities of the BND [German intelligence]
or the CIA, it was mercilessly blocked.
No information, no cooperation, nothing!
That's when I was first taken aback.[/font]

[font=Arial]Q: Schalck-Golodkowski mediated, among other things, various
business deals abroad. When you looked at his case more closely--[/font]

[font=Arial]Von Buelow: We found, for example, a clue in Rostock,
where Schalck organized his weapons depot.
Well, then we happened upon an affiliation of Schalck in Panama,
and then we happened upon Manuel Noriega,
who was for many years President, drug dealer,
and money launderer, all in one, right?
And this Noriega was also on the payroll of the CIA,
for $200,000 a year.
These were things that really made me curious.[/font]

[font=Arial]Q: You wrote a book on the dealings of the CIA and Co.
In the meantime, you have become an expert
regarding the strange things
related to intelligence services' work.[/font]

[font=Arial]Von Buelow: ``Strange things'' is the wrong term.
What has gone on, and goes on, in the name of intelligence services, are true crimes.[/font]

[font=Arial]Q: What would you say determines
the work of intelligence services?[/font]

[font=Arial]Von Buelow: So that we don't have any misunderstandings:
I find that it makes sense to have intelligence services....[/font]

[font=Arial]Q: You don't think much of the earlier proposals
by the Greens, who wanted to dismantle these agencies?[/font]

[font=Arial]Von Buelow: No. It is right to take a look
behind the scenes. Getting intelligence about the intentions
of an enemy, makes sense. It is important when one tries
to put oneself into the mind of the enemy.
Whoever wants to understand the CIA's methods,
has to deal with its main tasks, {covert operations}:
below the level of war, and outside international law,
foreign states are to be influenced, by organizing insurrections,
terrorist attacks, usually combined with drugs and weapons trade,
and money laundering. This is essentially very simple:
One arms violent people with weapons.
Since, however, it must not under any circumstances come out,
that there is an intelligence agency behind it,
all traces are erased, with tremendous deployment of resources.[/font]

[font=Arial]I have the impression
that this kind of intelligence agency spends 90% of its time
this way: creating false leads. So that, if anyone suspects
the collaboration of the agencies,
he is accused of the sickness of conspiracy madness.
The truth often comes out only years later.
CIA chief Allen Dulles once said:
In case of doubt, I would even lie to the Congress![/font]

[font=Arial]Q: The American journalist Seymour M. Hersh,
wrote in the {New Yorker,} that even some people in the CIA
and government assumed, that certain leads had been laid
in order to confuse the investigators.
Who, Herr von Buelow, would have done this?[/font]

[font=Arial]Von Buelow: I don't know that either. How should I?
I simply use my common sense, and--
See: The terrorists behaved in such a way to attract attention.
And as practicing Muslims, they were in a strip-tease bar,
and, drunken, stuck dollar bills into the panty of the dancer.[/font]

[font=Arial]Q: Things like that also happen.[/font]

[font=Arial]Von Buelow: It may be. As a lone fighter,
I cannot prove anything, that's beyond my capabilities.
I have real difficulties, however,
to imagine that all this all sprung
out ofthe mind of an evil man in his cave.[/font]

[font=Arial]Q: Mr. von Buelow, you yourself say
that you are alone in your criticism.
Formerly, you were part of the political establishment,
now you are an outsider.[/font]

[font=Arial]Von Buelow: That is a problem sometimes,
but one gets used to it. By the way,
I know a lot of people, including very influential ones,
who agree with me, but only in whispers, never publicly.[/font]

[font=Arial]Q: Do you still have contact with old SPD companions,
such as Egon Bahr and former Chancellor Helmut Schmidt?[/font]

[font=Arial]Von Buelow: There are no close contacts any more.
I wantedto go to the last SPD party congress, but I was sick.[/font]

[font=Arial]Q: Can it be, Mr. von Buelow, that you are a mouthpiece for
typical anti-Americanism?[/font]

[font=Arial]Von Buelow: Nonsense, this has absolutely nothing to do
with anti-Americanism. I am a great admirer of this great,
open, free society, and always have been. I studied in the U.S.[/font]

[font=Arial]Q: How did you get the idea that there could be a link
between the attacks and the American intelligence agencies?[/font]

[font=Arial]Von Buelow: Do you remember the first attack
on the WorldTrade Center in 1993?[/font]

[font=Arial]Q: Six people were killed and over a thousand wounded,
by a bomb explosion.[/font]

[font=Arial]Von Buelow: In the middle was the bombmaker,
a former Egyptian officer.
He had pulled together some Muslims for the attack.
They were snuck into the country by the CIA,
despite a State Department ban on their entry.
At the same time, the leader of the band was an FBI informant.[/font]

[font=Arial]And he made a deal with the authorities:
At the last minute, the dangerous explosive material
would be replaced by a harmless powder.[/font]

[font=Arial]The FBI did not stick to the deal.
The bomb exploded, so to speak, with the knowledge of the FBI.
The official story of the crime was quickly found:
The criminals were evil Muslims.[/font]

[font=Arial]Q: At the time Soviet soldiers marched into Afghanistan,
you were in the cabinet of Helmut Schmidt. What was it like?[/font]

[font=Arial]Von Buelow: The Americans pushed for trade sanctions,
they demanded the boycott of the Olympic games in Moscow....[/font]

[font=Arial]Q.... which the German government followed...[/font]

[font=Arial]Von Buelow: And today we know: It was the strategy
of the American security adviser, Zbigniew Brzezinski,
to destabilize the Soviet Union from neighboring Muslim countries
They lured the Russians into Afghanistan,
and then prepared for them a hell on earth, their Vietnam.
With decisive support of the U.S. intelligence agencies,
at least 30,000 Muslim fighters were trained
in Afghanistan and Pakistan, a bunch of good-for-nothings
and fanatics who were, and still are today, ready for anything.[/font]

[font=Arial]And one of them is Osama bin Laden. I wrote years ago: `
`It was out of this brood, that the Taliban grew up
in Afghanistan, who had been brought up in the Koran schools
financed by American and Saudi funds,
the Taliban who are now terrorizing the country and destroying it[/font]

[font=Arial]Q: Even though you say, for the U.S.
it was a matter of raw materials in the region,
the starting point for the U.S. aggression,
was the terrorist attack which cost thousands of human lives.[/font]

[font=Arial]Von Buelow: Completely true. One must always keep this
gruesome act in mind. Nonetheless, in the analysis of political
processes, I am allowed to look and see who has advantages
and disadvantages, and what is coincidental. When in doubt,
it is always worthwhile to take a look at a map,
where are raw materials resources, and the routes to them?
Then lay a map of civil wars and conflicts on top of that
--they coincide. The same is the case with the third map:
nodal points of the drug trade.[/font]

[font=Arial]Where this all comes together, the American intelligence services
are not far away. By the way, the Bush family is linked to oil,
gas, and weapons trade, through the bin Laden family.[/font]

[font=Arial]Q: What do you think of the Bin Laden films?[/font]

[font=Arial]Von Buelow: When one is dealing with intelligence services,
one can imagine manipulations of the highest quality.
Hollywood could provide these techniques.
I consider the videos inappropriate as evidence.[/font]

[font=Arial]Q: You believe the CIA is capable of anything,
[wouldn't stop at anything].[/font]

[font=Arial]Von Buelow: The CIA, in the state interests of the U.S.,
does not have to abide by any law in interventions abroad,
is not bound by international law;
only the President gives orders.[/font]

[font=Arial]And when funds are cut, peace is on the horizon,
then a bomb explodes somewhere. Thus it is proven,
that you can't do without the intelligence services;
and that the critics are {nuts,} as Father Bush called them,
Bush who was once CIA head and President.[/font]

[font=Arial]You have to see that the U.S. spends $30 billion
on intelligence services, and $13 billion on anti-drug work.
And what comes out of it?[/font]

[font=Arial]The chief of a special unit of the strategic anti-drug work declared, in despair, after 30 years of service,
that in every big, important drug case,
the CIA came in and took it out of my hands. (Rosalinda: Michael Levin)[/font]

[font=Arial]Q: Do you criticize the German government
for its reaction after Sept. 11?[/font]

[font=Arial]Von Buelow: No. To assume that the government
were independent in these questions, would be naive.[/font]

[font=Arial]Q: Herr von Buelow, what will you do now?[/font]

[font=Arial]Von Buelow: Nothing. My task is concluded by saying,
it could not have been that way [according to the official story]
Search for the truth![/font]

[illwill]

Oorspronkelijk geplaatst door democratsteve

Je bent rond de pot aan't draaien Steve.
Dat kan dat toch niet! bweu bweu bweu
ZOU JE NIET EENS EINDELIJK OPHOUDEN MET LULLEN!!!!!!!!!!!!
ZOU JE NIET EERST EENS ANTWOORDEN OP DE VRAGEN IN DE TWEE LANGE POSTS;
EN VOORAL. ZOU JE NIET EENS OPHOUDEN MET BESCHULDIGINGEN NAAR 'M HOOFD TE SLINGEREN DIE NERGEN OP SLAAN EN ZOU JE DAN ALS LAATSTE WILLEN OPHOUDEN MET ZELF LEUGENS TE VERTELLEN.

ALSTUBLIEFT!!!! VAN HUN EIGEN WEBSITE!!!!!!

Journal of Engineering Mechanics ASCE, in press
[size=3]9/13/01[/size], Expanded 9/22/01, Appendices 9/28/01)
Why Did the World Trade Center Collapse?—Simple Analysis
By Zdenek P. Bazant1, Fellow ASCE, and Yong Zhou2

Abstract: This paper3 presents a simplified approximate analysis of the overall collapse of the towers of World Trade Center in New York on September 11, 2001. The analysis shows that if prolonged heating caused the majority of columns of a single floor to lose their load carrying capacity, the whole tower was doomed. The structural resistance is found to be an order of magnitude less than necessary for survival, even though the most optimistic simplifying assumptions are introduced.

Introduction and Failure Scenario
The 110-story towers of the World Trade Center were designed to withstand as a whole the forces caused by a horizontal impact of a large commercial aircraft (Appendix I). So why did a total collapse occur? The cause was the dynamic consequence of the prolonged heating of the steel columns to very high temperature. The heating lowered the yield strength and caused viscoplastic (creep) buckling of the columns of the framed tube along the perimeter of the tower and of the columns in the building core. The likely scenario of failure is approximately as follows.

In stage 1 (Fig. 1), the conflagration caused by the aircraft fuel spilled into the structure causes the steel of the columns to be exposed to sustained temperatures apparently exceeding 800°C. This assumption is crucial to the entire analysis, and there is no basis for it. Actual tests of uninsulated steel structures exposed to gas and diesel fuel for sustained periods never exceeded 360°C. And widespread flames were no longer visible in either tower when it collapsed, only dark smoke. The heating is probably accelerated by a loss of the protective thermal insulation of steel during the initial blast. Blast? By implying that the impact fireballs were blasts, the authors confuse explosions, which produce very high pressures, with fireballs, which don't. A detonation wave can be generated by the sudden ignition of an unburned hydrocarbon-air mixture, but is not produced when ignition is continuous, as appeared to be the case with the dispersing fuel in the jet impacts. The fireballs took about two seconds to expand. Had they detonated, they would have appeared in milliseconds. At such temperatures, structural steel suffers a decrease of yield strength and exhibits significant viscoplastic deformation (i.e., creep—an increase of deformation under sustained load). This leads to creep buckling of columns (e.g., Bazant and Cedolin 1991, Sec. 9), which consequently lose their load carrying capacity (stage 2). Once more than about a half of the columns in the critical floor that is heated most suffer buckling (stage 3), the weight of the upper part of the structure above this floor can no longer be supported, and so the upper part starts falling down onto the lower part below the critical floor, gathering speed until it impacts the lower part. This flies in the face of engineering practice, which makes things at least four times as strong as they would have to be to sustain maximum anticipated loads. Actual load conditions were a fraction of those anticipated loads, since it was not a windy day, and the floors above the impacts were holding only a fraction of their rated capacities. So 90% would be a more realistic estimate of the needed column failure rate. At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity. The vertical impact of the mass of the upper part onto the lower part (stage 4) applies enormous vertical dynamic load on the underlying structure, far exceeding its load capacity, even if it is not heated. This causes failure of an underlying multi-floor segment of the tower (stage 4), in which the failure of the connections of the floor-carrying trusses to the columns is either accompanied or quickly followed by buckling of the core columns and overall buckling of the framed tube, was it too fast to see on the videos, or was it behind the dust? with the buckles probably spanning the height of many floors (stage 5, at right), and the upper part possibly getting wedged inside an emptied lower part of the framed tube (stage 5, at left). The buckling is initially plastic but quickly leads to fracture in the plastic hinges. When will they learn to use metal instead of plastic hinges!? The part of building lying beneath is then impacted again by an even larger mass falling with a greater velocity, and the series of impacts and failures then proceeds all the way down (stage 5).

Elastic Dynamic Plastic Fantastic Analysis
The details of the failure process after the decisive initial trigger that sets the upper part in motion are of course very complicated and their clarification would require large computer simulations. For example, the upper part of one tower is tilting as it begins to fall (see Appendix II); the distribution of impact forces among the underlying columns of the framed tube and the core, and between the columns and the floor-supporting trusses, is highly nonuniform; etc. However, a computer is not necessary to conclude that the collapse of the majority of columns of one floor must have caused the whole tower to collapse. This may be demonstrated by the following elementary calculations, in which simplifying assumptions most optimistic in regard to survival are made. That's a preposterous claim, since it's not even clear that elastic dynamic analysis, whatever it is, is even remotely applicable.

For a short time after the vertical impact of the upper part, but after the elastic wave generated by the vertical impact has propagated to the ground, the lower part of the structure can be approximately considered to act as an elastic spring (Fig. 2a). What is its stiffness C? It can vary greatly with the distribution of the impact forces among the framed tube columns, between these columns and those in the core, and between the columns and the trusses supporting concrete floor slabs.

For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally. Unlikely though such a distribution may be, it is nevertheless the most optimistic hypothesis to make because the resistance of the building to the impact is, for such a distribution, the highest. If the building is found to fail under a uniform distribution of the impact forces, it would fail under any other distribution. They cleverly insert the idea of uniform symmetric collapse -- one of the most obvious problems with the gravity-collapse -- as an optimistic hypothesis. According to this hypothesis, one may estimate that C 71 GN/m (due to unavailability of precise data, an approximate design of column cross sections had to be carried out for this purpose).

The downward displacement from the initial equilibrium position to the point of maximum deflection of the lower part (considered to behave elastically) is h + (P/C) where P = maximum force applied by the upper part on the lower part and h = height of critical floor columns (= height of the initial fall of the upper part) 3.7 m. The energy dissipation, particularly that due to the inelastic deformation of columns during the initial drop of the upper part, may be neglected, i.e., the upper part may be assumed to move through distance h almost in a free fall (indeed, the energy dissipated in the columns during the fall is at most equal to 2πX the yield moment of columns, X the number of columns, which is found to be only about 12% of the gravitational potential energy release if the columns were cold, and much less than that at 800°C). What is the the yield moment of the columns, and how many columns are there? The confidence of the authors in their conclusions is strinking, given the lack of any clear details of the tower's structures. Well, this 12% isn't the only thing we have to take their word for. So the loss of the gravitational potential energy of the upper part may be approximately equated to the strain energy of the lower part at maximum elastic deflection. This gives the equation mg[h + (P/C)] = P2/2C in which m = mass of the upper part (of North Tower) 58·106 kg, and g = gravity acceleration. The solution P = Pdyn yields the following elastically calculated overload ratio due to impact of the upper part:



where P0 = mg = design load capacity. In spite of the approximate nature of this analysis, it is obvious that the elastically calculated forces in columns caused by the vertical impact of the upper part must have exceeded the load capacity of the lower part by at least an order of magnitude.

Another estimate, which gives the initial overload ratio that exists only for a small fraction of a second at the moment of impact, is



where A = cross section area of building, Eef= cross section stiffness of all columns divided by A, ρ = specific mass of building per unit volume. This estimate is calculated from the elastic wave equation which yields the intensity of the step front of the downward pressure wave caused by the impact if the velocity of the upper part at the moment of impact on the critical floor is considered as the boundary condition (e.g., Bazant and Cedolin, Sec. 13.1). After the wave propagates to the ground, the former estimate is appropriate.

An important hypothesis implied in this analysis is that the impacting upper part, many floors in height, is so stiff that it does not bend nor shear on vertical planes, and that the distribution of column displacements across the tower is almost linear, like for a rigid body. If, however, the upper part spanned only a few floors (say, 3 to 6), then it could be so flexible that different column groups of the upper part could move down separately at different times, producing a series of small impacts that would not be fatal (in theory, if people could have escaped from the upper part of the tower, the bottom part of the tower could have been saved if the upper part were bombed, exploded or weakened by some "smart" structure mechanism to collapse onto the lower part gradually as a pile of rubble, instead of impacting it instantly as an almost rigid body). Just what we need! Smart-collapsing buildings. You many want to wear a hardhat if you go to work in one of these buildings because that falling rubble can hurt!

Analysis of Inelastic Energy Dissipation Ideation
The inelastic deformation of the steel of the towers involves plasticity and fracture. Since we are not attempting to model the details of the real failure mechanism but seek only to prove that the towers must have collapsed and do so in the way seen (Engineering 2001, American 2001), we will here neglect fracture, even though the development of fractures is clearly discerned in the photographs of the collapse. I see a lot of fractured steel but no sign of fractures developing -- just a progression of explosions down the building fracturing the frame along the way. Assuming the steel to behave plastically, with unlimited ductility, we are making the most optimistic assumption with regard to the survival capacity of the towers (in reality, the plastic hinges, especially the hinges at column connections, must have fractured, and done so at relatively small rotation, causing the load capacity to drop drastically).

The basic question to answer is: Can the fall of the upper part be arrested by energy dissipation during plastic buckling which follows the initial elastic deformation? Many plastic failure mechanisms could be considered, for example: (a) the columns of the underlying floor buckle locally (Fig. 1, stage 2); (b) the floor-supporting trusses are sheared off at the connections to the framed tube and the core columns and fall down within the tube, depriving the core columns and the framed tube of lateral support, and thus promoting buckling of the core columns and the framed tube under vertical compression (Fig. 1, stage 4, Fig. 2c); and how long would those massive core columns remain standing after losing the lateral support of the perimeter wall? I think more than the one second they did. or (c) the upper part is partly wedged within the emptied framed tube of the lower part, pushing the walls of the framed tube apart (Fig. 1, stage 5). That would keep the cores of the falling and intact portions aligned, so the core columns would have been crushing themselves as they went down. Although each of these mechanism can be shown to lead to total collapse, (I wish I were as smart as these guys so I could see too.) a combination of the last two seems more realistic (the reason: multi-story pieces of the framed tube, with nearly straight boundaries apparently corresponding to plastic hinge lines causing buckles on the framed tube wall, were photographed falling down; see, e.g., Engineering 2001, American 2001).

Regardless of the precise failure mode, experience with buckling indicates that the while many elastic buckles simultaneously coexist in an axially compressed tube, the plastic deformation localizes (because of plastic bifurcation) into a single buckle at a time (Fig. 1, stage 4; Fig. 2c), and so the buckles must fold one after another. Thus, at least one plastic hinge, and no more than four plastic hinges, per column line are needed to operate simultaneously in order to allow the upper part to continue moving down (Fig. 2b, Bazant and Cedolin 1991) (this is also true if the columns of only one floor are buckling at a time). At the end, the sum of the rotation angles θi (i = 1, 2, . . ) of the hinges on one column line, Σθi, cannot exceed 2π (Fig. 2b). This upper-bound value, which is independent of the number of floors spanned by the buckle, is used in the present calculations since, in regard to survival, it represents the most optimistic hypothesis, maximizing the plastic energy dissipation.

Calculating the dissipation per column line of the framed tube as the plastic bending moment Mp of one column (Jirasek and Bazant 2002), times the combined rotation angle θi = 2π (Fig. 2b), and multiplying this by the number of columns, one concludes that the plastically dissipated energy Wp is, optimistically, of the order of 0.5 GN m (for lack of information, certain details such as the wall thickness of steel columns, were estimated by carrying out approximate design calculations for this building).

To attain the combined rotation angle Σθi = 2π of the plastic hinges on each column line, the upper part of the building must move down by the additional distance of one buckle, which is at least one floor below the floor where the collapse started. So the additional release of gravitational potential energy Wg ≥ mg · 2h 2 X 2:1 GN m = 4.2 GN m. To arrest the fall, the kinetic energy of the upper part, which is equal to the potential energy release for a fall through the height of at least two floors, would have to be absorbed by the plastic hinge rotations of one buckle, i.e., Wg=Wp would have to be less than 1. Rather,



if the energy dissipated by the columns of the critical heated floor is neglected. If the first buckle spans over n floors (3 to 10 seems likely), this ratio is about n times larger. So, even under by far the most optimistic assumptions, the plastic deformation can dissipate only a small part of the kinetic energy acquired by the upper part of building.

When the next buckle with its group of plastic hinges forms, the upper part has already traveled many floors down and has acquired a much higher kinetic energy; the percentage of the kinetic energy dissipated plastically is then of the order of 1%. This claim is probably ridiculous, but in any case I can't find an argument that the elastic dynamic analysis and its plastic hinges applies even remotely to those structures. The percentage continues to decrease further as the upper part moves down. If fracturing in the plastic hinges were considered, a still smaller (in fact much smaller) energy dissipation would be obtained. So the collapse of the tower must be an almost free fall. This conclusion is supported by the observation that the duration of the collapse of the tower, observed to be 9 s, was about the same as the duration of a free fall in a vacuum from the tower top (416 m above ground) to the top of the final heap of debris (about 25 m above ground), which is It further follows that the brunt of vertical impact must have gone directly into the columns of the framed tube and the core and that any delay Δt of the front of collapse of the framed tube behind the front of collapsing (‘pancaking’) floors must have been negligible, or else the duration of the total collapse of the tower, 9 s + Δt, would have been significantly longer than 9 s. However, even for a short delay Δt, the floors should have acted like a piston running down through an empty tube, which helps to explain the smoke and debris that was seen being expelled laterally from the collapsing tower. Huh? Is this supposed to explain how the towers' tops crushed a 1000-foot high pillar of resilient steel as if there was only air there?

Problems of Disaster Mitigation and Design
Designing tall buildings to withstand this sort of attack seems next to impossible. If by "this sort of attack" they mean explosive demolition, I would agree. It would require a much thicker insulation of steel, with blast-resistant protective cover. No, that's useless, because they could cut away the protective cover when they place the explosives. Replacing the rectangular framed tube by a hardened circular monolithic tube with tiny windows might help to deflect much of the debris and fuel from an impacting aircraft sideways, but regardless of cost, who would want to work in such a building? I think most people would settle for a collapse-proof building.

The problems appear to be equally severe for concrete columns because concrete heated to such temperatures undergoes explosive thermal spalling, thermal fracture and disintegration due to dehydration of hardened cement paste (e.g., Bazant and Kaplan 1996). These questions arise not only for buildings supported on many columns but also for the recent designs of tall buildings with a massive monolithic concrete core functioning as a tubular mast. These recent designs use high-strength concrete which, however, is even more susceptible to explosive thermal spalling and thermal fracture than normal concrete. The use of refractory concretes as the structural material invites many open questions (Bazant and Kaplan 1996). Special alloys or various refractory ceramic composites may of course function at such temperatures, but the cost would increase astronomically. It will nevertheless be appropriate to initiate research on materials and designs that would postpone the collapse of the building so as to extend the time available for evacuation, because even though multi-story steel structures have never "collapsed" before 9-11, now their collapse will be inevitable in the event of fire. provide a hardened and better insulated stairwell, or even prevent collapse in the case of a less severe attack such as an off-center impact or the impact of an aircraft containing little fuel. Lessons should be drawn for improving the safety of building design in the case of lesser disasters. For instance, in view of the progressive dynamic collapse of a stack of all the floors of the Ronan Point apartments in the U.K., caused by a gas explosion in one upper floor (Levy and Salvadori 1992), the following design principle, determining the appropriate ff of redundancy, should be adopted: If only a certain judiciously specified minority of the columns or column-floor connections at one floor are removed, the mass that might fall down from the superior structure must be so small that its impact on the underlying structure would not cause dynamic overload.

Closing Comments
Once accurate computer calculations are carried out, various details of the failure mechanism will doubtless be found to differ from the present simplifying hypotheses. Errors by a factor of 2 would not be terribly surprising, but that would hardly matter since the present analysis reveals order-of-magnitude differences between the dynamic loads and the structural resistance. There have been many interesting, but intuitive, competing explanations of the collapse. Theorists were very busy between September 11th and 13th! To decide their viability, however, it is important to do at least some crude calculations. For example, it has been suggested that the connections of the floor-supporting trusses to the framed tube columns were not strong enough. Maybe they were not, but even if they were it would have made no difference, as shown by the present simple analysis.

But stay tuned, because once that 800 Cº figure in this paper gets noticed, the trusses and their connectors will be heavily relied on in a more fine-tuned official explanation.
The main purpose of the present analysis is to prove that the whole tower must have collapsed if the fire destroyed the load capacity of the majority of columns of a single floor. This purpose justifies the optimistic simplifying assumptions regarding survival made at the outset, which include unlimited plastic ductility (i.e., absence of fracture), uniform distribution of impact forces among the columns, disregard of various complicating details (e.g., the possibility that the failures of floor-column connections and of core columns preceded the column and tube failure, or that the upper tube got wedged inside the lower tube), etc. If the tower is found to fail under these very optimistic assumptions, it will certainly be found to fail when all the detailed mechanisms are analyzed, especially since there are order-of-magnitude differences between the dynamic loads and the structural resistance.

An important puzzle at the moment is why the adjacent 46-story building, into which no significant amount of aircraft fuel could have been injected, collapsed as well. Despite the lack of data at present, the likely explanation seems to be that high temperatures (though possibly well below 800°C) persisted on at least one floor of that building for a much longer time than specified by the current fire code provisions.

Appendix I. Elastic Dynamic Response to Aircraft Impact
A simple estimate based on the preservation of the combined momentum of the impacting Boeing 767-200 ( 179,000 kg X 550 km/h) and the momentum of the equivalent mass Meq of the interacting upper part of the tower ( 141 ·106 X v0 ) indicates that the initial average velocity v0 imparted to the upper part of the tower was only about 0.7 km/h = 0.19 m/s. Mass Meq, which is imagined as a concentrated mass mounted at the height of the impacted floor on a massless free-standing cantilever with the same bending stiffness as the tower (Fig. 2d), has been calculated from the condition that its free vibration period be equal to the first vibration period of the tower, which has been roughly estimated as T1 = 14 s (Meq 44% of the mass of the whole tower). The dynamic response after impact may be assumed to be dominated by the first free vibration mode, of period T1. Therefore, the maximum horizontal deflection w0 = v0Ti/2π 0.4 m, which is well within the design range of wind-induced elastic deflections. So it is not surprising that the aircraft impact per se damaged the tower only locally.

The World Trade Center was designed for an impact of Boeing 707-320 rather than Boeing 767-320. But note that the maximum takeoff weight of that older, less effcient, aircraft is only 15% less than that of Boeing 767-200. Besides, the maximum fuel tank capacity of that aircraft is only 4% less. These differences are well within the safety margins of design. So the observed response of the towers proves the correctness of the original dynamic design. What was not considered in design was the temperature that can develop in the ensuing fire. Here the lulling experience from 1945 might have been deceptive; that year, a two-engine bomber (B-25), flying in low clouds to Newark at about 400 km/h, hit the Empire State Building (381 m tall, built in 1932) at the 79th floor (278 m above ground)—the steel columns (much heavier than in modern buildings) suffered no significant damage, and the fire remained confined essentially to two floors only (Levy and Salvadori 1992).

Appendix II. Why Didn’t the Upper Part Pivot About Its Base?
Since the top part of the South Tower tilted (Fig. 3a), many people wonder: Why didn’t the upper part of the tower fall to the side like a tree, pivoting about the center of the critical floor? Before wading into the following mumbo-jumbo it's worth noting that once the top of the tower started its vertical plunge, its rate of rotation slowed down. This can only be explained by the breakup of the top (the piston used above to "explain" the near free-fall rate of destruction) which would have destroyed its moment of inertia. (Fig. 3b) To demonstrate why, and thus to justify our previous neglect of tilting, is an elementary exercise in dynamics. Assume the center of the floor at the base of the upper part (Fig. 3b) to move for a while neither laterally nor vertically, i.e., act as a fixed pivot. Equating the kinetic energy of the upper part rotating as a rigid body about the pivot at its base (Fig. 3c) to the loss of the gravitational potential energy of that part (which is here simpler than using the Lagrange equations of motion), we have where x is the vertical coordinate (Fig. 3c). 5 This provides



where θ = rotation angle of the upper part, H1 = its height, and the superposed dots denote time derivatives (Fig. 3c). Considering the dynamic equilibrium of the upper part as a free body, acted upon by distributed inertia forces and a reaction with horizontal component F at base (Fig. 3d), one obtains . Evidently, the maximum horizontal reaction during pivoting occurs for θ = 45°, and so



where, for the upper part of South Tower, m 87 · 106 kg.

Could the combined plastic shear resistance Fp of the columns of one floor (Fig. 3f) sustain this horizontal reaction? For plastic shear, there would be yield hinges on top and bottom of each resisting column; Fig. 3e (again, aiming only at an optimistic upper bound on resistance, we neglect fracture). The moment equilibrium condition for the column as a free body shows that each column can at most sustain the shear force F1 = 2Mp/h1 where h1 2:5 m = effective height of column, and Mp 0:3 MN m = estimated yield bending moment of one column, if cold. Assuming that the resisting columns are only those at the sides of the framed tube normal to the axis of rotation, which number about 130, we get Fp 130F1 31 MN. So, the maximum horizontal reaction to pivoting would cause the overload ratio



if the resisting columns were cold. Since they are hot, the horizontal reaction to pivoting would exceed the shear capacity of the heated floor still much more (and far more if fracture were considered).

Since F is proportional to sin 2θ, its value becomes equal to the plastic limit when sin 2θ = 1/10.3. From this we further conclude that the reaction at the base of the upper part of South Tower must have begun shearing the columns plastically already at the inclination



The pivoting of the upper part must have started by an asymmetric failure of the columns on one side of building, but already at this very small angle the dynamic horizontal reaction at the base of the upper part must have reduced the vertical load capacity of the remaining columns of the critical floor (even if those were not heated). That must have started the downward motion of the top part of the South Tower, and afterwards its motion must have become predominantly vertical. Hence, a vertical impact of the upper part onto the lower part must have been the dominant mechanism.

Finally note that the horizontal reaction Fmax is proportional to the weight of the pivoting part. Therefore, if a pivoting motion about the center of some lower floor were considered, Fmax would be still larger.

Appendix III. Plastic Load-Shortening Diagram of Columns
Normal design deals only with initial bifurcation and small deflections, in which the diagram of load versus axial shortening of an elasto-plastic column exhibits hardening rather than softening. However, the columns of the towers suffered very large plastic deflections, for which this diagram exhibits pronounced softening. Fig. 5 shows this diagram as estimated for these towers. The diagram begins with axial shortening due to plastic yielding at load P10 = A1fi where A1 = crosssection area of one column and fy = yield limit of steel. At the axial shortening of about 3%, there is a plastic bifurcation (if imperfections are ignored). After that, undeflected states are unstable and three plastic hinges (Fig. 5) must form (if we assume, optimistically, the ends to be fixed). From 6 the condition of moment equilibrium of the half-column as a free body (Fig. 5), the axial load then is P1 = 4Mp/L sinθ, while, from the buckling geometry, the axial shortening is u = L(1 - cosθ), where L = distance between the end hinges. Eliminating plastic hinge rotation θ, we find that the plastic load-shortening diagram (including the pre- and post-bifurcation states) is given by



which defines the curve plotted in Fig. 5. This curve is an optimistic upper bound since, in reality, the plastic hinges develop fracture (e.g., Bazant and Planas 1998), and probably do so already at rather small rotations. The area under this curve represents the dissipated energy.

If it is assumed that one or several floor slabs above the critical heated floor collapsed first, then the L to be substituted in (8) is much longer than the height of columns of one floor. Consequently, P1(u) becomes much smaller (and the Euler elastic critical load for buckling may even become less than the plastic load capacity, which is far from true when L is the column height of a single floor).

It has been suggested that the inelastic deformation of columns might have ‘cushioned’ the initial descent of the upper part, making it almost static. However, this is impossible because, for gravity loading, a softening of the load-deflection diagram (Fig. 5) always causes instability and precludes static deformation (Bazant and Cedolin 1991, Chpt. 10 and 13). The downward acceleration of the upper part is ü = N[P10 - P1(u)]/m where N = number of columns and, necessarily, P10 = mg/N. This represents a differential equation for u as a function of time t, and its integration shows that the time that the upper part takes to fall through the height of one story is, for cold columns, only about 6% longer than the duration of a free fall from that height, which is 0.87 s. For hot columns, the difference is of course much less than 6%. So there is hardly any ‘cushioning’.

Wil je in het vervolg eens aub gewoon de link geven, je moet hier tegenwoordig een half uur scrollen om nog eens een nieuwe posting te kunnen lezen.

[Bristow]

Oorspronkelijk geplaatst door exodus

Het zijn zogezegd allemaal toevallen en flaters. Dat is hoe de non-believers 9/11 verklaren.. Ze denken natuurlijk dat de believers het serieus mis hebben en te veel fantasie hebben.

Hieronder een interview met een voormalige Duitse minister. In de jaren 80 onderzocht hij geheime diensten zoals Stasi en KGB, hij is een kenner op het gebied van inlichtingendiensten.

Lees eens wat die man zegt. Is hij ook een fantast die het toaal mis heeft??

Ja.

Zie bijvoorbeeld hier: [font=Verdana]http://www.spiegel.de/international/...265160,00.html [/font]


Kom toch eens af met echte bewijzen, niet hallucinaties van complottheoretici.
Probeer eens te tonen waar de officiële verslagen over WTC 1/2 en het Pentagon verkeerd zitten.

(Illwill heeft gelijk. Geef liever links dan ellenlange citaten. Een kort citaat is handig, lange niet.)

[nadine]

Oorspronkelijk geplaatst door democratsteve

Je bent rond de pot aan't draaien Steve.
Dat kan dat toch niet! bweu bweu bweu
ZOU JE NIET EENS EINDELIJK OPHOUDEN MET LULLEN!!!!!!!!!!!!
ZOU JE NIET EERST EENS ANTWOORDEN OP DE VRAGEN IN DE TWEE LANGE POSTS;
EN VOORAL. ZOU JE NIET EENS OPHOUDEN MET BESCHULDIGINGEN NAAR 'M HOOFD TE SLINGEREN DIE NERGEN OP SLAAN EN ZOU JE DAN ALS LAATSTE WILLEN OPHOUDEN MET ZELF LEUGENS TE VERTELLEN.

ALSTUBLIEFT!!!! VAN HUN EIGEN WEBSITE!!!!!!

Journal of Engineering Mechanics ASCE, in press
[SIZE=3]9/13/01[/SIZE], Expanded 9/22/01, Appendices 9/28/01)
Why Did the World Trade Center Collapse?—Simple Analysis
By Zdenek P. Bazant1, Fellow ASCE, and Yong Zhou2

Abstract: This paper3 presents a simplified approximate analysis of the overall collapse of the towers of World Trade Center in New York on September 11, 2001. The analysis shows that if prolonged heating caused the majority of columns of a single floor to lose their load carrying capacity, the whole tower was doomed. The structural resistance is found to be an order of magnitude less than necessary for survival, even though the most optimistic simplifying assumptions are introduced.

Introduction and Failure Scenario
The 110-story towers of the World Trade Center were designed to withstand as a whole the forces caused by a horizontal impact of a large commercial aircraft (Appendix I). So why did a total collapse occur? The cause was the dynamic consequence of the prolonged heating of the steel columns to very high temperature. The heating lowered the yield strength and caused viscoplastic (creep) buckling of the columns of the framed tube along the perimeter of the tower and of the columns in the building core. The likely scenario of failure is approximately as follows.

In stage 1 (Fig. 1), the conflagration caused by the aircraft fuel spilled into the structure causes the steel of the columns to be exposed to sustained temperatures apparently exceeding 800°C. This assumption is crucial to the entire analysis, and there is no basis for it. Actual tests of uninsulated steel structures exposed to gas and diesel fuel for sustained periods never exceeded 360°C. And widespread flames were no longer visible in either tower when it collapsed, only dark smoke. The heating is probably accelerated by a loss of the protective thermal insulation of steel during the initial blast. Blast? By implying that the impact fireballs were blasts, the authors confuse explosions, which produce very high pressures, with fireballs, which don't. A detonation wave can be generated by the sudden ignition of an unburned hydrocarbon-air mixture, but is not produced when ignition is continuous, as appeared to be the case with the dispersing fuel in the jet impacts. The fireballs took about two seconds to expand. Had they detonated, they would have appeared in milliseconds. At such temperatures, structural steel suffers a decrease of yield strength and exhibits significant viscoplastic deformation (i.e., creep—an increase of deformation under sustained load). This leads to creep buckling of columns (e.g., Bazant and Cedolin 1991, Sec. 9), which consequently lose their load carrying capacity (stage 2). Once more than about a half of the columns in the critical floor that is heated most suffer buckling (stage 3), the weight of the upper part of the structure above this floor can no longer be supported, and so the upper part starts falling down onto the lower part below the critical floor, gathering speed until it impacts the lower part. This flies in the face of engineering practice, which makes things at least four times as strong as they would have to be to sustain maximum anticipated loads. Actual load conditions were a fraction of those anticipated loads, since it was not a windy day, and the floors above the impacts were holding only a fraction of their rated capacities. So 90% would be a more realistic estimate of the needed column failure rate. At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity. The vertical impact of the mass of the upper part onto the lower part (stage 4) applies enormous vertical dynamic load on the underlying structure, far exceeding its load capacity, even if it is not heated. This causes failure of an underlying multi-floor segment of the tower (stage 4), in which the failure of the connections of the floor-carrying trusses to the columns is either accompanied or quickly followed by buckling of the core columns and overall buckling of the framed tube, was it too fast to see on the videos, or was it behind the dust? with the buckles probably spanning the height of many floors (stage 5, at right), and the upper part possibly getting wedged inside an emptied lower part of the framed tube (stage 5, at left). The buckling is initially plastic but quickly leads to fracture in the plastic hinges. When will they learn to use metal instead of plastic hinges!? The part of building lying beneath is then impacted again by an even larger mass falling with a greater velocity, and the series of impacts and failures then proceeds all the way down (stage 5).

Elastic Dynamic Plastic Fantastic Analysis
The details of the failure process after the decisive initial trigger that sets the upper part in motion are of course very complicated and their clarification would require large computer simulations. For example, the upper part of one tower is tilting as it begins to fall (see Appendix II); the distribution of impact forces among the underlying columns of the framed tube and the core, and between the columns and the floor-supporting trusses, is highly nonuniform; etc. However, a computer is not necessary to conclude that the collapse of the majority of columns of one floor must have caused the whole tower to collapse. This may be demonstrated by the following elementary calculations, in which simplifying assumptions most optimistic in regard to survival are made. That's a preposterous claim, since it's not even clear that elastic dynamic analysis, whatever it is, is even remotely applicable.

For a short time after the vertical impact of the upper part, but after the elastic wave generated by the vertical impact has propagated to the ground, the lower part of the structure can be approximately considered to act as an elastic spring (Fig. 2a). What is its stiffness C? It can vary greatly with the distribution of the impact forces among the framed tube columns, between these columns and those in the core, and between the columns and the trusses supporting concrete floor slabs.

For our purpose, we may assume that all the impact forces go into the columns and are distributed among them equally. Unlikely though such a distribution may be, it is nevertheless the most optimistic hypothesis to make because the resistance of the building to the impact is, for such a distribution, the highest. If the building is found to fail under a uniform distribution of the impact forces, it would fail under any other distribution. They cleverly insert the idea of uniform symmetric collapse -- one of the most obvious problems with the gravity-collapse -- as an optimistic hypothesis. According to this hypothesis, one may estimate that C 71 GN/m (due to unavailability of precise data, an approximate design of column cross sections had to be carried out for this purpose).

The downward displacement from the initial equilibrium position to the point of maximum deflection of the lower part (considered to behave elastically) is h + (P/C) where P = maximum force applied by the upper part on the lower part and h = height of critical floor columns (= height of the initial fall of the upper part) 3.7 m. The energy dissipation, particularly that due to the inelastic deformation of columns during the initial drop of the upper part, may be neglected, i.e., the upper part may be assumed to move through distance h almost in a free fall (indeed, the energy dissipated in the columns during the fall is at most equal to 2πX the yield moment of columns, X the number of columns, which is found to be only about 12% of the gravitational potential energy release if the columns were cold, and much less than that at 800°C). What is the the yield moment of the columns, and how many columns are there? The confidence of the authors in their conclusions is strinking, given the lack of any clear details of the tower's structures. Well, this 12% isn't the only thing we have to take their word for. So the loss of the gravitational potential energy of the upper part may be approximately equated to the strain energy of the lower part at maximum elastic deflection. This gives the equation mg[h + (P/C)] = P2/2C in which m = mass of the upper part (of North Tower) 58·106 kg, and g = gravity acceleration. The solution P = Pdyn yields the following elastically calculated overload ratio due to impact of the upper part:



where P0 = mg = design load capacity. In spite of the approximate nature of this analysis, it is obvious that the elastically calculated forces in columns caused by the vertical impact of the upper part must have exceeded the load capacity of the lower part by at least an order of magnitude.

Another estimate, which gives the initial overload ratio that exists only for a small fraction of a second at the moment of impact, is



where A = cross section area of building, Eef= cross section stiffness of all columns divided by A, ρ = specific mass of building per unit volume. This estimate is calculated from the elastic wave equation which yields the intensity of the step front of the downward pressure wave caused by the impact if the velocity of the upper part at the moment of impact on the critical floor is considered as the boundary condition (e.g., Bazant and Cedolin, Sec. 13.1). After the wave propagates to the ground, the former estimate is appropriate.

An important hypothesis implied in this analysis is that the impacting upper part, many floors in height, is so stiff that it does not bend nor shear on vertical planes, and that the distribution of column displacements across the tower is almost linear, like for a rigid body. If, however, the upper part spanned only a few floors (say, 3 to 6), then it could be so flexible that different column groups of the upper part could move down separately at different times, producing a series of small impacts that would not be fatal (in theory, if people could have escaped from the upper part of the tower, the bottom part of the tower could have been saved if the upper part were bombed, exploded or weakened by some "smart" structure mechanism to collapse onto the lower part gradually as a pile of rubble, instead of impacting it instantly as an almost rigid body). Just what we need! Smart-collapsing buildings. You many want to wear a hardhat if you go to work in one of these buildings because that falling rubble can hurt!

Analysis of Inelastic Energy Dissipation Ideation
The inelastic deformation of the steel of the towers involves plasticity and fracture. Since we are not attempting to model the details of the real failure mechanism but seek only to prove that the towers must have collapsed and do so in the way seen (Engineering 2001, American 2001), we will here neglect fracture, even though the development of fractures is clearly discerned in the photographs of the collapse. I see a lot of fractured steel but no sign of fractures developing -- just a progression of explosions down the building fracturing the frame along the way. Assuming the steel to behave plastically, with unlimited ductility, we are making the most optimistic assumption with regard to the survival capacity of the towers (in reality, the plastic hinges, especially the hinges at column connections, must have fractured, and done so at relatively small rotation, causing the load capacity to drop drastically).

The basic question to answer is: Can the fall of the upper part be arrested by energy dissipation during plastic buckling which follows the initial elastic deformation? Many plastic failure mechanisms could be considered, for example: (a) the columns of the underlying floor buckle locally (Fig. 1, stage 2); (b) the floor-supporting trusses are sheared off at the connections to the framed tube and the core columns and fall down within the tube, depriving the core columns and the framed tube of lateral support, and thus promoting buckling of the core columns and the framed tube under vertical compression (Fig. 1, stage 4, Fig. 2c); and how long would those massive core columns remain standing after losing the lateral support of the perimeter wall? I think more than the one second they did. or (c) the upper part is partly wedged within the emptied framed tube of the lower part, pushing the walls of the framed tube apart (Fig. 1, stage 5). That would keep the cores of the falling and intact portions aligned, so the core columns would have been crushing themselves as they went down. Although each of these mechanism can be shown to lead to total collapse, (I wish I were as smart as these guys so I could see too.) a combination of the last two seems more realistic (the reason: multi-story pieces of the framed tube, with nearly straight boundaries apparently corresponding to plastic hinge lines causing buckles on the framed tube wall, were photographed falling down; see, e.g., Engineering 2001, American 2001).

Regardless of the precise failure mode, experience with buckling indicates that the while many elastic buckles simultaneously coexist in an axially compressed tube, the plastic deformation localizes (because of plastic bifurcation) into a single buckle at a time (Fig. 1, stage 4; Fig. 2c), and so the buckles must fold one after another. Thus, at least one plastic hinge, and no more than four plastic hinges, per column line are needed to operate simultaneously in order to allow the upper part to continue moving down (Fig. 2b, Bazant and Cedolin 1991) (this is also true if the columns of only one floor are buckling at a time). At the end, the sum of the rotation angles θi (i = 1, 2, . . ) of the hinges on one column line, Σθi, cannot exceed 2π (Fig. 2b). This upper-bound value, which is independent of the number of floors spanned by the buckle, is used in the present calculations since, in regard to survival, it represents the most optimistic hypothesis, maximizing the plastic energy dissipation.

Calculating the dissipation per column line of the framed tube as the plastic bending moment Mp of one column (Jirasek and Bazant 2002), times the combined rotation angle θi = 2π (Fig. 2b), and multiplying this by the number of columns, one concludes that the plastically dissipated energy Wp is, optimistically, of the order of 0.5 GN m (for lack of information, certain details such as the wall thickness of steel columns, were estimated by carrying out approximate design calculations for this building).

To attain the combined rotation angle Σθi = 2π of the plastic hinges on each column line, the upper part of the building must move down by the additional distance of one buckle, which is at least one floor below the floor where the collapse started. So the additional release of gravitational potential energy Wg ≥ mg · 2h 2 X 2:1 GN m = 4.2 GN m. To arrest the fall, the kinetic energy of the upper part, which is equal to the potential energy release for a fall through the height of at least two floors, would have to be absorbed by the plastic hinge rotations of one buckle, i.e., Wg=Wp would have to be less than 1. Rather,



if the energy dissipated by the columns of the critical heated floor is neglected. If the first buckle spans over n floors (3 to 10 seems likely), this ratio is about n times larger. So, even under by far the most optimistic assumptions, the plastic deformation can dissipate only a small part of the kinetic energy acquired by the upper part of building.

When the next buckle with its group of plastic hinges forms, the upper part has already traveled many floors down and has acquired a much higher kinetic energy; the percentage of the kinetic energy dissipated plastically is then of the order of 1%. This claim is probably ridiculous, but in any case I can't find an argument that the elastic dynamic analysis and its plastic hinges applies even remotely to those structures. The percentage continues to decrease further as the upper part moves down. If fracturing in the plastic hinges were considered, a still smaller (in fact much smaller) energy dissipation would be obtained. So the collapse of the tower must be an almost free fall. This conclusion is supported by the observation that the duration of the collapse of the tower, observed to be 9 s, was about the same as the duration of a free fall in a vacuum from the tower top (416 m above ground) to the top of the final heap of debris (about 25 m above ground), which is It further follows that the brunt of vertical impact must have gone directly into the columns of the framed tube and the core and that any delay Δt of the front of collapse of the framed tube behind the front of collapsing (‘pancaking’) floors must have been negligible, or else the duration of the total collapse of the tower, 9 s + Δt, would have been significantly longer than 9 s. However, even for a short delay Δt, the floors should have acted like a piston running down through an empty tube, which helps to explain the smoke and debris that was seen being expelled laterally from the collapsing tower. Huh? Is this supposed to explain how the towers' tops crushed a 1000-foot high pillar of resilient steel as if there was only air there?

Problems of Disaster Mitigation and Design
Designing tall buildings to withstand this sort of attack seems next to impossible. If by "this sort of attack" they mean explosive demolition, I would agree. It would require a much thicker insulation of steel, with blast-resistant protective cover. No, that's useless, because they could cut away the protective cover when they place the explosives. Replacing the rectangular framed tube by a hardened circular monolithic tube with tiny windows might help to deflect much of the debris and fuel from an impacting aircraft sideways, but regardless of cost, who would want to work in such a building? I think most people would settle for a collapse-proof building.

The problems appear to be equally severe for concrete columns because concrete heated to such temperatures undergoes explosive thermal spalling, thermal fracture and disintegration due to dehydration of hardened cement paste (e.g., Bazant and Kaplan 1996). These questions arise not only for buildings supported on many columns but also for the recent designs of tall buildings with a massive monolithic concrete core functioning as a tubular mast. These recent designs use high-strength concrete which, however, is even more susceptible to explosive thermal spalling and thermal fracture than normal concrete. The use of refractory concretes as the structural material invites many open questions (Bazant and Kaplan 1996). Special alloys or various refractory ceramic composites may of course function at such temperatures, but the cost would increase astronomically. It will nevertheless be appropriate to initiate research on materials and designs that would postpone the collapse of the building so as to extend the time available for evacuation, because even though multi-story steel structures have never "collapsed" before 9-11, now their collapse will be inevitable in the event of fire. provide a hardened and better insulated stairwell, or even prevent collapse in the case of a less severe attack such as an off-center impact or the impact of an aircraft containing little fuel. Lessons should be drawn for improving the safety of building design in the case of lesser disasters. For instance, in view of the progressive dynamic collapse of a stack of all the floors of the Ronan Point apartments in the U.K., caused by a gas explosion in one upper floor (Levy and Salvadori 1992), the following design principle, determining the appropriate ff of redundancy, should be adopted: If only a certain judiciously specified minority of the columns or column-floor connections at one floor are removed, the mass that might fall down from the superior structure must be so small that its impact on the underlying structure would not cause dynamic overload.

Closing Comments
Once accurate computer calculations are carried out, various details of the failure mechanism will doubtless be found to differ from the present simplifying hypotheses. Errors by a factor of 2 would not be terribly surprising, but that would hardly matter since the present analysis reveals order-of-magnitude differences between the dynamic loads and the structural resistance. There have been many interesting, but intuitive, competing explanations of the collapse. Theorists were very busy between September 11th and 13th! To decide their viability, however, it is important to do at least some crude calculations. For example, it has been suggested that the connections of the floor-supporting trusses to the framed tube columns were not strong enough. Maybe they were not, but even if they were it would have made no difference, as shown by the present simple analysis.

But stay tuned, because once that 800 Cº figure in this paper gets noticed, the trusses and their connectors will be heavily relied on in a more fine-tuned official explanation.
The main purpose of the present analysis is to prove that the whole tower must have collapsed if the fire destroyed the load capacity of the majority of columns of a single floor. This purpose justifies the optimistic simplifying assumptions regarding survival made at the outset, which include unlimited plastic ductility (i.e., absence of fracture), uniform distribution of impact forces among the columns, disregard of various complicating details (e.g., the possibility that the failures of floor-column connections and of core columns preceded the column and tube failure, or that the upper tube got wedged inside the lower tube), etc. If the tower is found to fail under these very optimistic assumptions, it will certainly be found to fail when all the detailed mechanisms are analyzed, especially since there are order-of-magnitude differences between the dynamic loads and the structural resistance.

An important puzzle at the moment is why the adjacent 46-story building, into which no significant amount of aircraft fuel could have been injected, collapsed as well. Despite the lack of data at present, the likely explanation seems to be that high temperatures (though possibly well below 800°C) persisted on at least one floor of that building for a much longer time than specified by the current fire code provisions.

Appendix I. Elastic Dynamic Response to Aircraft Impact
A simple estimate based on the preservation of the combined momentum of the impacting Boeing 767-200 ( 179,000 kg X 550 km/h) and the momentum of the equivalent mass Meq of the interacting upper part of the tower ( 141 ·106 X v0 ) indicates that the initial average velocity v0 imparted to the upper part of the tower was only about 0.7 km/h = 0.19 m/s. Mass Meq, which is imagined as a concentrated mass mounted at the height of the impacted floor on a massless free-standing cantilever with the same bending stiffness as the tower (Fig. 2d), has been calculated from the condition that its free vibration period be equal to the first vibration period of the tower, which has been roughly estimated as T1 = 14 s (Meq 44% of the mass of the whole tower). The dynamic response after impact may be assumed to be dominated by the first free vibration mode, of period T1. Therefore, the maximum horizontal deflection w0 = v0Ti/2π 0.4 m, which is well within the design range of wind-induced elastic deflections. So it is not surprising that the aircraft impact per se damaged the tower only locally.

The World Trade Center was designed for an impact of Boeing 707-320 rather than Boeing 767-320. But note that the maximum takeoff weight of that older, less effcient, aircraft is only 15% less than that of Boeing 767-200. Besides, the maximum fuel tank capacity of that aircraft is only 4% less. These differences are well within the safety margins of design. So the observed response of the towers proves the correctness of the original dynamic design. What was not considered in design was the temperature that can develop in the ensuing fire. Here the lulling experience from 1945 might have been deceptive; that year, a two-engine bomber (B-25), flying in low clouds to Newark at about 400 km/h, hit the Empire State Building (381 m tall, built in 1932) at the 79th floor (278 m above ground)—the steel columns (much heavier than in modern buildings) suffered no significant damage, and the fire remained confined essentially to two floors only (Levy and Salvadori 1992).

Appendix II. Why Didn’t the Upper Part Pivot About Its Base?
Since the top part of the South Tower tilted (Fig. 3a), many people wonder: Why didn’t the upper part of the tower fall to the side like a tree, pivoting about the center of the critical floor? Before wading into the following mumbo-jumbo it's worth noting that once the top of the tower started its vertical plunge, its rate of rotation slowed down. This can only be explained by the breakup of the top (the piston used above to "explain" the near free-fall rate of destruction) which would have destroyed its moment of inertia. (Fig. 3b) To demonstrate why, and thus to justify our previous neglect of tilting, is an elementary exercise in dynamics. Assume the center of the floor at the base of the upper part (Fig. 3b) to move for a while neither laterally nor vertically, i.e., act as a fixed pivot. Equating the kinetic energy of the upper part rotating as a rigid body about the pivot at its base (Fig. 3c) to the loss of the gravitational potential energy of that part (which is here simpler than using the Lagrange equations of motion), we have where x is the vertical coordinate (Fig. 3c). 5 This provides



where θ = rotation angle of the upper part, H1 = its height, and the superposed dots denote time derivatives (Fig. 3c). Considering the dynamic equilibrium of the upper part as a free body, acted upon by distributed inertia forces and a reaction with horizontal component F at base (Fig. 3d), one obtains . Evidently, the maximum horizontal reaction during pivoting occurs for θ = 45°, and so



where, for the upper part of South Tower, m 87 · 106 kg.

Could the combined plastic shear resistance Fp of the columns of one floor (Fig. 3f) sustain this horizontal reaction? For plastic shear, there would be yield hinges on top and bottom of each resisting column; Fig. 3e (again, aiming only at an optimistic upper bound on resistance, we neglect fracture). The moment equilibrium condition for the column as a free body shows that each column can at most sustain the shear force F1 = 2Mp/h1 where h1 2:5 m = effective height of column, and Mp 0:3 MN m = estimated yield bending moment of one column, if cold. Assuming that the resisting columns are only those at the sides of the framed tube normal to the axis of rotation, which number about 130, we get Fp 130F1 31 MN. So, the maximum horizontal reaction to pivoting would cause the overload ratio



if the resisting columns were cold. Since they are hot, the horizontal reaction to pivoting would exceed the shear capacity of the heated floor still much more (and far more if fracture were considered).

Since F is proportional to sin 2θ, its value becomes equal to the plastic limit when sin 2θ = 1/10.3. From this we further conclude that the reaction at the base of the upper part of South Tower must have begun shearing the columns plastically already at the inclination



The pivoting of the upper part must have started by an asymmetric failure of the columns on one side of building, but already at this very small angle the dynamic horizontal reaction at the base of the upper part must have reduced the vertical load capacity of the remaining columns of the critical floor (even if those were not heated). That must have started the downward motion of the top part of the South Tower, and afterwards its motion must have become predominantly vertical. Hence, a vertical impact of the upper part onto the lower part must have been the dominant mechanism.

Finally note that the horizontal reaction Fmax is proportional to the weight of the pivoting part. Therefore, if a pivoting motion about the center of some lower floor were considered, Fmax would be still larger.

Appendix III. Plastic Load-Shortening Diagram of Columns
Normal design deals only with initial bifurcation and small deflections, in which the diagram of load versus axial shortening of an elasto-plastic column exhibits hardening rather than softening. However, the columns of the towers suffered very large plastic deflections, for which this diagram exhibits pronounced softening. Fig. 5 shows this diagram as estimated for these towers. The diagram begins with axial shortening due to plastic yielding at load P10 = A1fi where A1 = crosssection area of one column and fy = yield limit of steel. At the axial shortening of about 3%, there is a plastic bifurcation (if imperfections are ignored). After that, undeflected states are unstable and three plastic hinges (Fig. 5) must form (if we assume, optimistically, the ends to be fixed). From 6 the condition of moment equilibrium of the half-column as a free body (Fig. 5), the axial load then is P1 = 4Mp/L sinθ, while, from the buckling geometry, the axial shortening is u = L(1 - cosθ), where L = distance between the end hinges. Eliminating plastic hinge rotation θ, we find that the plastic load-shortening diagram (including the pre- and post-bifurcation states) is given by



which defines the curve plotted in Fig. 5. This curve is an optimistic upper bound since, in reality, the plastic hinges develop fracture (e.g., Bazant and Planas 1998), and probably do so already at rather small rotations. The area under this curve represents the dissipated energy.

If it is assumed that one or several floor slabs above the critical heated floor collapsed first, then the L to be substituted in (8) is much longer than the height of columns of one floor. Consequently, P1(u) becomes much smaller (and the Euler elastic critical load for buckling may even become less than the plastic load capacity, which is far from true when L is the column height of a single floor).

It has been suggested that the inelastic deformation of columns might have ‘cushioned’ the initial descent of the upper part, making it almost static. However, this is impossible because, for gravity loading, a softening of the load-deflection diagram (Fig. 5) always causes instability and precludes static deformation (Bazant and Cedolin 1991, Chpt. 10 and 13). The downward acceleration of the upper part is ü = N[P10 - P1(u)]/m where N = number of columns and, necessarily, P10 = mg/N. This represents a differential equation for u as a function of time t, and its integration shows that the time that the upper part takes to fall through the height of one story is, for cold columns, only about 6% longer than the duration of a free fall from that height, which is 0.87 s. For hot columns, the difference is of course much less than 6%. So there is hardly any ‘cushioning’.

Ik geef ook Illwill en Bristow volledig gelijk over die ellenlange citaten. Niemand leest nog wat je eigenlijk zelf denkt te vertellen, en het hilarisch aspect van je bijdragen geraakt er volledig verloren bij.

[exodus]

Oorspronkelijk geplaatst door Bristow

Ja.

Zie bijvoorbeeld hier: [font=Verdana]http://www.spiegel.de/international/...265160,00.html [/font]


Kom toch eens af met echte bewijzen, niet hallucinaties van complottheoretici.

Nogmaals , dit is uw overtuiging. Dat artikel is niet meer dan de overtuiding van de auteur. Er wordt met slijk gesmeten maar er wordt geen motivatie aangehaald. Het is pure propaganda.

Oorspronkelijk geplaatst door Bristow

Probeer eens te tonen waar de officiële verslagen over WTC 1/2 en het Pentagon verkeerd zitten.

DemocratSteve heeft dat al deels gedaan in zijn lange posts. (Waar jullie totaal niet op ingaan, ik vraag me zelfs af als je ze leest.)

[Bristow]

Oorspronkelijk geplaatst door exodus

DemocratSteve heeft dat al deels gedaan in zijn lange posts. (Waar jullie totaal niet op ingaan, ik vraag me zelfs af als je ze leest.)

Neen en Ja (in de juiste volgorde).

Ik herhaal:

Kom toch eens af met echte bewijzen, niet hallucinaties van complottheoretici.

Probeer eens te tonen waar de [size=3]officiële verslagen[/size] over WTC 1/2 en het Pentagon verkeerd zitten.

[Gun]

Oorspronkelijk geplaatst door exodus

DemocratSteve heeft dat al deels gedaan in zijn lange posts. (Waar jullie totaal niet op ingaan, ik vraag me zelfs af als je ze leest.)

@Exodus,

Bristow heeft reeds eerder verklaard dat hij de lange posts niet leest

@ Bristow,

Ook ik denk dat Exodus het hier bij het rechte eind heeft. U zou ze eens moeten lezen, ... maar dan wel met de oogkleppen op de nachtkast.

Nogmaals, het is hier geen wedstrijd die moet gewonnen worden, het gaat hier niet over wie al dan niet het gelijk volledig aan zijn kant heeft. Ik geloofde in eerste instantie ook geen bal van wat er op bepaalde sites terecht kwam, tot ik mij dieper en dieper ben gaan informeren. U slaagt nagels met koppen wanneer U bepaalde berichten zwaar onder vuur neemt, maar het halstarrig vast houden aan de officiële kanalen bewijst voor een stuk uw kategorische ingesteldheid.

Eigen ervaring: neem ff afstand van uw eigen ideeën, zet de deur op een kier voor het in twijfel trekken van de officiële data en van langs om meer komt er u informatie tegemoet dat aangeeft dat er gefoefeld is. Dit geeft niet onmiddellijk een antwoord op de ware toedracht, maar verduidelijkt heel wat rand-toestanden in de jonge geschiedenis van dit planeetje.

@ All,

Ik heb de indruk dat één of ander jonge dame mij nog steeds achtervolgt met valse beschuldigingen aan mijn adres. Ik kan alleen maar melden dat ik de bewuste naam in mijn negeerbakje heb gedropt en dus geen van haar posts meer te lezen krijg. In den beginne was het moeilijk om aan de neiging tot lezen te weerstaan, maar men kan het vergelkijken met stoppen roken, ff moeilijk, maar het went snel. Ik kan alleen in alle eer en geweten zeggen dat ik niets gecopieerd heb van op andere forums, noch op andere forums iets van die aard heb gepost.

[Knipp]

Oorspronkelijk geplaatst door 2004gun

maar het halstarrig vast houden aan de officiële kanalen bewijst voor een stuk uw kategorische ingesteldheid.

een heel klein beetje kategorische ingesteldheid zou anders wel wonderen doen voor jullie duizendpuzzelstukjesurbanjunglegeesten

ik heb hier overigens niemand de officiële kanalen zien verheerlijken,
alleen is het alsmaar duidelijker dat de officiële kanalen verklaringen bieden die coherenter zijn en beter onderbouwd zijn

en wordt alsmaar duidelijker dat jullie het vertikken
met n coherent verhaal te komen en volharden in het posten van ellenlange lijsten losse feiten, toevalligheden, niet te controleren beweringen

in feite bewijzen jullie daarmee (in de ogen van de meeste mensen) de geloofwaardigheid van de officiële kanalen,
en missen jullie dus met brio je eigen doel

ik kan jullie maar 1 advies geven, als je mensen tot n meer kritische houding vs officiële kanalen wil bewegen, kom dan met sobere zeer goed onderbouwde stellingen, niet
met duizend losse flodders waarvan driekwart eerder op de lachspieren werkt

[Gun]

Oorspronkelijk geplaatst door Knipp

een heel klein beetje kategorische ingesteldheid zou anders wel wonderen doen voor jullie duizendpuzzelstukjesurbanjunglegeesten

ik heb hier overigens niemand de officiële kanalen zien verheerlijken,
alleen is het alsmaar duidelijker dat de officiële kanalen verklaringen bieden die coherenter zijn en beter onderbouwd zijn

en wordt alsmaar duidelijker dat jullie het vertikken met 'n coherent verhaal te komen en volharden in het posten van ellenlange lijsten losse feiten, toevalligheden, niet te controleren beweringen

U hoeft van dit forum de laatste 50 posts eens snel te doorlopen om een 10-tal verheerlijkingen op te solferen:

- Zowel voor WTC 1/2 en het Pentagon zijn alle technische vragen wel degelijk beantwoord. (WTC 7 moet nog komen.)
- Ik denk dat je steeds verwijst naar initiële verslagen, niet naar de uitvoerige analyses die door het NIST worden uitgevoerd, en die trouwens nog niet definitief zijn. Dat van WTC 7 is nog helemaal niet gepubliceerd.
- Het NIST is nu bezig met een heel uitvoerig wetenschappelijk onderzoek. Als je denkt dat al die wetenschappers en onderzoekers oneerlijk zijn, soit.
- Ik hecht inderdaad meer geloof in erkende experts op allerlei gebieden uit gereputeerde universiteiten dan in crack-pots.
- Hoe officieel is een artikel dat op 13/9/2001 wordt gepubliceerd ?
- Hoe gefundeerd is een analyse die 13/9/2001 wordt gepubliceerd ?
- De officiële verslagen, de gefundeerde wetenschappelijke analyses zijn natuurlijk veel later gekomen, en zijn nog niet eens af.
- Als je wist wat wetenschappelijk onderzoek inhoudt dan zou je dat zonder meer begrijpen.

Voor een coherent verhaal heb je ellenlange posts nodig

[Knipp]

Oorspronkelijk geplaatst door 2004gun

U hoeft van dit forum de laatste 50 posts eens snel te doorlopen om een 10-tal verheerlijkingen op te solferen:

Wat jij verheerlijking van de officiële kanalen noemt, klinkt in mijn oren alleen maar als n pleidooi voor n wetenschappelijke en kritische benadering.

Kritisch weetjewel, zonder oogkleppen...