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

为了弄清纽约世贸中心双子塔在9.11事件中遭到喷气式客机袭击后的倒塌过程，进行了数值模拟。随后是整体振动响应和局部破坏发展，导致结构发展的机制得到澄清，事实是南塔在完全倒塌前大约一个小时保持静止。已经进行了模型试验，以观察导致塔楼最终倒塌的渐进倒塌过程。结果表明，由密集排列的柱子组成的筒体结构可以承受自重荷载，至少可以防止瞬间倒塌，只要周柱由楼板和横梁体系横向支撑，满足日本标准2%的要求。在这方面提出了一个关于设计可能是主题…的建筑结构的命题更多的原因是冲击或爆炸载荷导致柱子失效。重点介绍了柱式重力承重体系，并将其分为两类。其中一组必须足够坚固，以保证不发生故障，而另一组可能发生部分故障，但仍对承载系统的重新分配和增加整个结构系统的冗余度做出贡献。对一座典型的20层钢筋混凝土建筑在一种情况下对小型飞机的撞击和在另一种情况下对中型喷气式飞机的响应进行了模拟。前者的结构反应相当于设计地震反应的1/10~1/30，而后者的冲击力最大超过受冲击楼层的水平承载能力，相当于设计地震反应的1/2~1/4。然而，在后一种情况下，不会发生层间倒塌，因为冲击持续时间比建筑物的基本振动周期短得多。较少

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