Disaster in relation to the Hanshin-Awaji earthquake: A comment on risk-informed design
Following the disastrous Hanshin-Awaji Great Earthquake, which occurred on 17 January 1995 and caused a loss of approximately 6000 lives and damage of more than US$100 billion, a concept of risk-informed design has gradually been discussed in Japan. This event, the so-called Kobe earthquake, brought unexpected structural damage to buildings and civil engineering structures. In Japan, the seismic design procedure of such structures had been developed to a high level, and various codes and guidelines had been established in approximately 40 fields including the Building Code. Even so, there was serious damage in a highly populated area of Kobe city, one of the most famous and beautiful port cities of Japan, stretching over several square kilometres. The author estimated that the probability of recurrence of such a serious event in the Kobe area will be less than one in 10 000 - 100 000 years, even if the cycle of occurrence of strong earthquake events is of the order of 1000 years. Accounting for the occurrence of such rare events, with extreme consequences, in structural design and in achieving control of structural behaviour during such an earthquake, is an extremely difficult engineering task. In general, the Design Code, designated by the Government or an engineering organization, defines the earthquake related design basis (DBE), and all structures must be designed based on the DBE. This is an absolute requirement in Japan. The concept of risk-informed design is based on the two issues that the endurance limit is left arbitrary and the 'level of design' (design as compared with the state-of-the-art) is defined through the outcome of negotiations between the future owner and the designer. Obviously, such a concept may lead to a variety of legal problems, and some of these are addressed here: e.g. (1), what kind of liability exists in case of failure of the structure designed and executed according to the 'level of design' selected and agreed upon by negotiation; (2), who is responsible in the case of an earthquake event which exceeds the 'design level' and causes loss of lives; and (3), even if there is no loss of life, by whom and how will the loss of material be covered? Also, what happens in a case when the total loss exceeds the capacity of a group of related insurance companies? The key issues, covering 30 years of experience of disaster prevention in Japan are discussed.
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