Performance-based reliability evaluation of structure-foundation systems

The most recent professional expectation is that the reliability of complicated mechanical or structural systems should be evaluated using their performances. In general, a complicated system consists of many elements, some of which act in series and others act in parallel. The failure of one element may not indicate the failure of the system. Furthermore, the brittle and ductile behaviors of elements after they reach their capacities also affect the overall reliability of the system. In most cases, strength performance requirements are satisfied at the element level and the serviceability or deflection requirements are satisfied at the structural level. For the performance-based reliability evaluation procedure, the element-level probabilities of unsatisfactory performance (UP) for strength and system-level probabilities of UP for serviceability need to be combined. A procedure is presented here to calculate the lower and upper bounds of the probability of failure of the system. A complicated structure-foundation system consisting of concrete superstructure and pile-supported foundation is considered to illustrate the procedure. The discussions indicate that the estimation of the probability of failure at the element level, particularly for the strength performance function often practised in the profession, may not be sufficient to develop performance-based design criteria.