Symptom-based reliability and generalized repairing cost in monitored bridges

This paper proposes the use of structural safety formulations conceived to take into account the presence of periodic monitoring systems. Monitoring is a valid tool to improve the safety of those structural systems that cannot withstand invasive tests or interventions that would alter their nature or their intended use. Reliability can be defined as a function of a measurable quantity that reflects the damage, referred to as symptom, and it can also be defined as a function of several symptoms considered simultaneously. A knowledge of the current value of a symptom makes it possible to determine the residual damage capacity and the residual lifetime of a structure. Redefining structural safety in terms of residual lifetime provides the theoretical framework for the introduction of vibration-based monitoring activities in probabilistic formulations. In the last part of the paper, by relating damage to reliability with respect to collapse, the generalized maintenance cost for a concrete bridge deck was analyzed in order to verify the economic advantages offered by dynamic monitoring.