ABSTRACT
Optimizat ion goals in engineering design are approached th rough empirical me thods , and the same is t rue of seismic design. In large scale s t ructural design the results of different trials are compared and the best selected. The o p t i m u m quant i ty should be least cost or max imum benefit. In practice, however, there is n o specific op t imum quant i ty or function, and ' op t imum' is most ly a subjective and fuzzy idea based on past experience. Engineers seem satisfied with the safety level of their present design, which is usually t aken as a s t andard in their evaluat ion of safety of new designs. Perhaps because of this implicit nature, safety level is generally not stated in quanti ta tive terms and the users of design codes do no t deal with it explicitly.
