Structural system reliability and optimization

Abstract

Structural reliability research concentrates on probabilistic descriptions of phenomena and application to code oriented safety design. Alternatively, optimization research works toward efficient algorithms for locating optima particularly in large-scale systems using prescribed deterministic constraints. This paper attempts to unify these efforts. Optimization procedures should explicitly consider safety either directly in its cost function or as one of its primary constraints. In the design of structural elements it is easier to establish the connection between optimization and reliability. Examples of element optimization in concrete structures and highway bridge girders elements subject to fatigue loading are discussed. In structural system problems, the complex interrelationship of elements and failure modes has made structural reliability analysis extremely difficult. The paper emphasizes the importance of characterizing systems with regard to a reliability oriented model including parallel, series, ductile, brittle, independent and correlated strength behavior. Following the developments in reliability formulation for elements the paper derives a second-moment reliability analysis for framewords leading to a step-by-step evaluation of the system reliability with a series of reanalysis of the structure. Since the reliability evaluation only requires a few reanalyses in most cases, the method is feasible for application in system optimization.