Reliability of Structures and Structural Systems

The safety and reliability of structures and structural systems are examined within the context of several physically plausible assumptions. Some fundamental results are derived to clarify the consequences of various assumptions pertaining to a system and its components on the reliability of a structure. Among these results are: (1) The risk function of a structure is shown to be a monotonically decreasing function of the number of loads sustained; thus, assuming a constant risk equal to the probability of failure to the first load leads to a safe estimate of the true reliability; (2) recognizing that the member forces in a structural system are always perfectly correlated, the reliability of a structural system is bounded above by the reliability computed on the assumption of perfectly correlated member strengths, and bounded below by the reliability computed on the assumption of statistically independent member strengths; and (3) the reliability computed on the usual assumption that the failure of members are statistically independent events invariably leads to an extremely conservative estimate of the true system reliability. As far as the survival of the original system is concerned, the treatment of statically indeterminate systems is the same as that of determinate systems.