Japan is well-known as an earthquake prone country. The safety level of
Japanese buildings is determined by their seismic performance. Buildings
also have value as social property, so that Japanese society expects a
certain seismic safety level. However, no socially explicit consensus
has yet been determined on a standard of seismic safety.
However since the Great Hanshin-Awaji Earthquake of 1995, building
users' voices have become louder in expressing their desire for a clear
indication of a seismic safety level that expresses a building's
expected seismic performance. The method of representing seismic safety
level can be understood by engineers, but this is difficult for users.
Users do not have a clear grasp of safety level. It is also difficult to
represent the seismic level of the whole building using only one safety
index. Thus there have been no attempts to use a single index. This
study was carried out to evaluate probabilistically a desirable target
seismic level from user questionnaires using a structural reliability
theory.
This paper attempts a quantitative evaluation based on social needs of
users for target seismic safety level. The results of this study show
how users' requirement levels can be indicated as a reliability index
beta. Answers on required reliability obtained from about six hundred
questionnaires of users from all over the country were analyzed, and
then a target level was calculated. Users request higher levels of
safety than are available at present. Engineers have never seen user
needs for social target level of building safety, but this new method
enables a socially desirable level to be evaluated quantitatively.