Abstract
The aim of this study is to develop a method of optimization of importance factor. We assume that building system is determined by three aspects, that is, physical, economical and social aspect. From a physical aspect, building system is denoted by physical variables; load effect S, strength R and magnifying factor of strengthθwhich is called importance factor. From an economical aspect, construction cost is a variable indicating a building system. From a social aspect, the social utilities of building system are represented fundamentally by an expected value of total utility during design life span of building under the failure probabilities determined by importance factor. Under the above formulation, we determine the value ofθcorresponding to the maximum total social utility. This problem is denoted by equation (9)〜(18). This system of equations follows equation (19). This equation means a principle at maximization of utility from a safety point of view.
