Shingo Nakanishi

Reliability design of structural system with cost effectiveness during life cycle

This study deals with an economic analysis of structural systems using a reliability-based design method. In this paper, a new expected total cost concept, which includes initial cost, cost of reliability test, annual maintenance cost, penalty cost for designers faults and losses by structural failure is proposed. In the proposed formulation, the minimum expected total cost during the life duration with the capital rate of interest and rate of price fluctuations could be evaluated by calculating the present currency and annual prediction procedure.

Evaluation Method of Statistical Uncertainties for Safety Index Based on Confidence Ellipsoid.

This paper deals with the problem of statistical uncertainties of safety index. Though a second moment safety index is widely used as a safety index for a probabilistic design code, it is impossible for this index to avoid to include intrinsically statistical variations since the random parameters are estimated only from the obtained field data or imperfect information. In this paper, the new measures for statistical uncertainties of safety index which is proposed as a confidence region is around the design point with the confidence level. These confidence regions of safety index are derived from an ellipsoid on super plane whose region corresponds to the value of confidence level. This paper shows that region for safety index can be mapped as the internal region of an ellipsoid on super plane. Therefore the region called as confidence ellipsoid.

Formulation of Economic Assessment for Optimum Design Based on Structural Reliability.

This study deals with an economic analysis of structural systems on using a reliability-based design method. Although the expected total cost which is composed of the initial cost and the cost of failure for the structural system has been investigated, it is crucial to consider the annual prediction cost with life cycle cost (LCC) during the life duration. It is also important to evaluate the cost not only on structural failure but also on designers faults. Furthermore, it is necessary that the cost of the reliability test is taken into account in determining the expected total cost because uncertainties of parameters are strongly dependent upon the quality control or material test. In this paper, a new expected total cost concept which includes the cost mentioned above is proposed. In the proposed formulation, an optimization problem for economic evaluation during the life duration with the capital rate of interest and rate of price fluctuations can be solved by applying the present currency and annual prediction concepts. For a comparative evaluation, from the numerical analyses of a truss bridge structure, it is pointed out that not only optimization by present value but also that by annual value is useful for decision making in practical design.