“Anti-Catastrophe” Concept in Japanese Seismic Design Codes

Abstract eng:
In light of the serious tsunami disaster during the 2011 Tohoku earthquake and the subsequent severe accident at the Fukushima-Daiichi Nuclear Power Plant, the preparedness of infrastructures such as railway structures, highway structures and port structures to unexpected events became a big issue among civil engineers in Japan. In the conventional seismic design of these structures, basically two kinds of design ground motions, namely, the level 1 and 2 design ground motions are considered and the structures are designed so that they fulfill respective performance requirements through verification. In particular, significantly intense ground motions from shallow crustal and subduction earthquakes have been considered as the level 2 design ground motions. However, it is still necessary to consider the performance of structures to unexpected events and its consequences, mainly because of our insufficient knowledge of natural phenomena and of the performance of structures itself. Therefore, the authors proposed a new design concept called the “anti-catastrophe design concept”. In this concept, a structure is said to be “anti-catastrophe” when the structure or the structure-environment system does not exhibit catastrophic situation even in an unexpected event. In order to contribute to the establishment of the “anti-catastrophe” design concept of structures, the design standards for railway structures, highway structures, and port structures in Japan are reviewed. In all of these codes, the necessity to consider the performance of structures to unexpected events and its consequences are recognized. For the railway structures, devices have been developed for the anti-catastrophe design including the “dead weight compensation mechanism”. For the highway structures, “unseating prevention devices” have widely been used in the design of bridges. For the port structures, efforts are being made to improve the performance of breakwaters after they are affected by extreme tsunamis. One of the most important ingredients of the “anti-catastrophe design” is to understand the performance of a structure or a structure-environment system under extreme external forces to understand its consequences. In this respect, the “anti-catastrophe design” is oriented in the same direction as the “riskinformed design” proposed in the revised version of ISO2394. However, as mentioned above, the Japanese engineers seem to put more emphasis on the development of measures or devices to cope with this issue. It should be noted that our knowledge is quite limited in terms of the performance of a structure or of a structure-environment system subject to extreme events. Obviously more effort is needed to understand the performance of structures to extreme events. To this end, every kind of available tools should be used. For example, model tests and numerical simulations could be useful. On the other hand, it is not reasonable to think that the performance of such devices or measures should always be evaluated quantitatively. Sometimes, other human abilities such as intuition and insight could be useful in developing measures and devices. As an example, although we do not know the detailed stress history of unseating prevention devices during an earthquake, they have widely been used in the design of highway bridges in Japan and some of those devices performed well in the past earthquakes. After all, we should mobilize all kinds of human ability, ranging from intuition or insight to more sophisticated engineering skills, to cope with the issue of the preparedness of structures to unexpected events.

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