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Case Studies of deliberate steel building implosions

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  • 19-03-2019 5:55pm
    #1
    Registered Users Posts: 81,996 ✭✭✭✭


    I thought maybe this thread would be handy to reference. Not really a debate about what happened to the World Trade Center, but just an objective observation of demolitions that have occurred of buildings that are potentially similar in nature, if one wishes to believe WTC's 1,2,and 7 (but not 5?) were taken down with surgical precision - and were somehow fundamentally required to achieve the same false-flag goal as just, crashing planes into buildings and letting the pieces fall where they may. I mean, if anyone wishes to explain that rationale to me I'll hear it out, but it's been 18.5 years and I haven't heard it yet.

    For this, I will ignore buildings that have collapsed partially or otherwise during fire events (eg. https://www.youtube.com/watch?v=8XMTALBYRNA, Building name/location unknown). I just want to focus on buildings which were deliberately imploded - actually rigged to come down with explosive charges. I will ignore implosions which have involved structures that were primarily concrete (eg. https://www.youtube.com/watch?v=_anYswmGMeM Ocean Tower in TX).

    I referenced the list from Wikipedia, List of tallest voluntarily demolished buildings, looking at buildings which were imploded - the key difference between most controlled explosive demolitions and an implosion is that an implosion involves demolishing the building down within its own footprint, not topped over to one side - the preferred, safer method of predicting a collapse mode when you have the room.

    "Sometimes, though, a building is surrounded by structures that must be preserved. In this case, the blasters proceed with a true implosion, demolishing the building so that it collapses straight down into its own footprint (the total area at the base of the building). This feat requires such skill that only a handful of demolition companies in the world will attempt it."


    How Stuff Works - Implosions

    Starting with the Landmark Tower in TX, demolished 2006.





    Landmark was a 'conventional steel frame with an aluminum curtain wall.'

    As can be seen evidently, the explosive force required is significant. There are a couple stages of charge which are clearly evident, the pops/flashes can be visibly seen running up and down each floor. There are also very large explosives particularly at the base. The noise generated is considerable, as are the visible explosive pyrotechnic blasts, etc.

    The second is the Sparkasse Hagen tower in Germany, imploded in 2004. It is a somewhat different construction: it has some steel framing but it is also largely reinforced by steel-reinforced-concrete shear wall panels. It's a relatively light construction, especially when partially demolished before the implosion. They rigged the 8th floor with explosives used the top of the building to help crush the bottom half.



    They had to cut away significant portions of the concrete shear wall to achieve this collapse mode before the implosion was done (see Fig. 3 in this conference paper)

    475852.PNG

    The paper (Computer Simulation for Building Implosion Using LS-DYNA) involved here is especially enlightening about the nature of performing these types of computer simulations - and they cut corners:

    "The experience gained from these [preliminary simulation] examples showed firstly that the element erosion-algorithm in the case of non vertical collapse scenarios, in which failure occurs mostly due to strong bending of elements and not due to high pressures, can provide reliable results, at least for the initial collapse kinematics. On the other hand, the erosion scheme should not be applied in the case of a vertical collapse, since as a result of removing elements it does not deliver reliable results. The node-split-algorithm, however, is more time consuming and imposes several changes in the discretization, but is a better alternative which delivers realistic results even in the case of vertical collapse with high pressures and material failure due to strong compression."

    [...]

    "The finite element model consists of 392481 8-node hexahedral solid elements. At first, the CAD geometry was created from the building drawings.
    Then, using the preprocessor Hypermesh [14], the finite element mesh was constructed and imported into LS-DYNA. At this final stage, all the numerical algorithms were applied, such as material model, element formulation etc. In the computations to be presented a rather simple, piecewise linear, plasticity model is used (LS-DYNA MAT24) for efficiency reasons. However, some limitations have to be mentioned resulting from the fairly simple failure criterion. In addition to that, it must be noted that also in the case when Node-Split is applied, a rather high resolution of the model is necessary in order to capture sufficiently the entire cracking process. Furthermore, by using continua for the modelling of reinforced concrete the effect of the steel bars is “smeared” in the continuum. E.g. the presence of steel bars, after the mechanical failure of the concrete, would in reality prevent structural parts from flying away from the structure. However, in the simulations when the continua fail, a complete dissolution is obtained. This results in general in an overly brittle behaviour and some elements are flying away from the structure, In the simulations we try to damp this motion which is not a perfect solution. The ground plate is simulated as a rigid body and the building collapses under the effect of gravity."


    The compute time for the final model was over 716 hours (29 days). Not including the time spent generating the CAD, mesh, and all the necessary modifications to stop the simulation from crashing out (and the time wasted on simulations that ultimately crashed out):

    "New contact interfaces are created and included in the search contact algorithm which is very time consuming and as a consequence slows down the entire computation. In order to remove the major part of the artificial energy which was added to the model during the application of the initial gravitation with explicit time integration, the system had to be damped for 0.1 second, otherwise large vibrations were leading to error terminations.

    It proved to be particularly important to avoid the “inversion” of solid elements leading to negative volumes and finally to error terminations, as a result of large element deformations. In order to handle this problem additional contact checks were added which consider contacts between interior surfaces of the hexahedral elements to avoid an inversion. Nevertheless, in the results the limitation in the applicability of the Node Split algorithm is observed from the very strong dissolution of element connections due to material failure, which creates for some parts unrealistic phenomena (structural parts flying e.t.c). The latter would not be possible with reinforcing steel which mostly prevents a complete dissolution of parts."


    (ie. they had no way to truly computationally model the destruction mode for reinforced concrete, so it was approximated heavily). Basically, these simulations are incredibly resource and time intensive, and difficult to work with even when you are reverse-engineering an implosion with all your conditions known with regard to explosives used and behavior during the collapse ex post facto. Note also this is a 2011 paper, and the simulation produced was not anything used to control the implosion of the building when it went down in 2004.


    ... and that brought me down through about #30 on the Wikipedia list, most of the entries are not implosions and/or involve concrete structure buildings. I will perhaps continue through the list if the thread is well received, this post took a moment longer than I thought it would.


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