The claim that the apartment building in Chennai (see post below) collapsed because of a lighting strike sounds- at first- far fetched, since such never was reported before. However, the Polytechnic Südwestfalen, Germany, made laboratory tests that showed that an enormous explosive power is mobilized, when the charge of a lighting jumps from one reinforcement iron to another (when not properly bound together). A possible lesson for engineers and builders in the industrialized countries as well.
© Polytechnic Südwestfalen, Prof. Dr.- Ing. Jan Meppelink
On 28th of June 2014 around 4:40 PM IST one of two under construction buildings collapsed at a suburb of Chennai, in the Indian state of Tamil Nadu. The collapse happened during heavy rain and a thunderstorm with lightning. The building site was still busy. Workers and casual uninvolved searched shelter from the rain and frequent lightning. This is the reason the accident claimed many victims, altogether 61 casualties. Many of the survivors delivered eye witness reports. According to those reports the building collapsed directly after a lightning stroke. This might be the first documented case where a lighting caused the complete collapse of a building.
The debris pattern is most unusual, since the building was split into two halves and each half shifted to the respective side. The simulation, made by Virtual Validation Corporation Kostack & Walter, reproduces this extraordinary dynamics very well. The software was developed at Laurea University of Applied Sciences.
Now, that we are able to successfully simulate the collapse of big building structures, the software Blender gives its splendid support to exploit the simulation results for interactive walk throughs. Blender´s powerful features facilitate educational tools for rescue workers and paramedics. A training program could teach them in localizing victims within the debris, estimating their physical condition and applying first aid measures.
We have reached an impressive milestone. Our BCB add-on has evolved into a serious simulation tool: One of the software validation cases in our Inachus research has been the collapsed Pyne Gould Corporation building in Christchurch. The building was destroyed in a devastating earthquake, on 22 February 2011. The Blender add-on was able to simulate the debris pattern fairly accurately as it can be seen from the video and the still images at the end of it.
Only the simulation of concrete structures is possible at the moment. Much remains to be done, such as the simulation of deformable building elements like steel structures. The bases is laid with the introduction of spring constraints. But the working of springs in Blender needs yet thorough investigation.
This video is a first test to see if our simulation results can be used in an interactive walk through environment. The collapsed blender model is exported into the unreal game engine. Here a character can walk around, climb the debris or search inside for cavity spaces. This technology would be perfectly suitable for the education of rescue personnel. It is for example possible to apply physical behavior to debris fragments so that trainees can move pieces and experience the subsequent collapse.
The simulation of the Yu- experiment, for the first time really put our work we have done so far to the test in terms of physical accuracy. We have built the beam with increasing discretization (subdivision) levels. We approximated the weight needed to break the setup by running multiple simulations for each subdivision level. We where very happy to see that the finally established weights of 5100, 5400, 4800, 5000 kg etc where all in a very close range compared to the real loading level of 4700kg in the original real world experiment. (maximal deviation +15%)
We emphasize that at the moment we do not track permanent plastic deformation or crack propagation. What at this stage is interesting to us is to evaluate if we can predict the absolute moment of breaking of a structural assembly. This first comparison with a real world experiment seems to indicate that this is the case.
To validate structural performance of reinforced concrete structures many tests on RC assemblages have been carried out under column removal scenarios. They provide valuable information on structural dynamic performance. One such experiments was executed at the Fraunhofer Institute for High-Speed Dynamics by following the specimen design by Jun Yu and Kang Hai Tan: A ca 6 meter long concrete beam supported by a center concrete pillar was loaded with a constant 47kN in form of two huge concrete block weights . The center pillar was then suddenly removed by explosives.
The research papers by the Fraunhofer Institute can be downloaded from here.