SIGNIFICANCE OF OPTIMUM DESIGN BASED ON RELIABILITY

The fundamental philosophy of structural design can be divided into two according to the criterion which defines the failure of a structure. One is the allowable stress design based on the initial failure of an individual member. The other is the design based on the ultimate strength of a structure. The design or the assessment of the safety of the structure can be further divided into deterministic and probabilistic approaches. However, regardless of these differences, the general goal of the design is an optimisation of the structure maintaining sufficient reliability. The authors studied optimum designs of truss structures based on the deterministic and the probabilistic estimation of the strength for both the initial failure and the ultimate failure criteria. A new probabilistic optimisation method based on the ultimate strength is proposed. It employs the idea of optimum distribution of safety indices for each failure mode. The significance of the optimum design based on the reliability is discussed through comparison with deterministic approaches.