Evaluation and Counter Measures on Resistant Capability of Important Structures against Impact and Blast Loads

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Numerical simulation has been carried out to make clear the collapsing process of twin towers at the New York World Trade Center, which was attacked by jet-liners in the 9.11 event. Overall vibratory response together with local damage development is followed, leading to the clarification of the structurally developed mechanism in the fact that the south tower remained standing still about an hour before complete collapse. A model experiment has been carried out to observe the process of progressive collapse that has led the towers to the final collapse. It has turned out that the tube structure composing of densely arranged columns along the perimeter could sustain gravity loads, at least preventing instantaneous collapse, provided the perimeter columns are supported transversely by the system of flooring and beams strongly enough to meet 2% requirement as specified in Japanese standard. A proposition is made in this connection for designing a building structure which might be subject … More ed to an impact or blast load suffering column failure. Attention is paid to the gravity load supporting system by columns, which are to be categorized into two groups. One group must be strong enough to remain without failure, whereas the other group may undergo partial failure, but still contributing to the redistribution of load bearing system, and to increasing the redundancy of the whole structural system.Simulation has been executed to reveal the response of a typical 20 story reinforced concrete building to the impact of a small airplane in one case and to medium size jet-liner in another. The structural response in the former corresponds to 1/10〜1/30 of the case of a design earthquake; whereas in the later, impact force reaches a maximum in excess of the horizontal load carrying capacity of the impacted story, corresponding to 1/2〜1/4 of the response to a design earthquake. In the latter, however, inter-story collapse does not occur, since the impacting duration is much shorter than the fundamental period of vibration of the building. Less