Reliability Assessment of Existing Concrete Bridges: Knowledge Uncertainties, Degradation Phenomena, and Seismic Risk

Bridges plays a fundamental role in global economic and social development and represents an essential function in daily life, allowing fast, efficient, and safe movement of people and goods. They primarily consist of aging structures that are aging, designed under old codes, and vulnerable to failures, as highlighted by recent collapses worldwide. The main challenge of research today is to develop efficient and effective assessment methods to evaluate the structural reliability of existing bridges. The knowledge uncertainties influence the reliability of existing bridges, because the statistical properties of the basic random variables are not known in advance, and they can be estimated from a limited number of imprecise tests. Among all bridges, the post tensioned (PT) concrete ones pose a particular challenge due to the high level of uncertainty of their state of conservation of the compression system. Existing bridges are also exposed to aggressive environmental conditions that induce degradation processes, such as corrosion induced by chloride diffusion, that reduce the structural performance. Corrosion degradation becomes more critical when linked with natural hazards such as earthquakes. By incorporating corrosion into seismic risk assessment the number of basic variables to be considered further increases, leading to greater system complexity and uncertainty over the time. This study aims to provide a comprehensive reliability assessment of existing bridges. First, the impact of knowledge uncertainties on reliability assessment is examined performing both the semi-probabilistic and the probabilistic approach, whit reference to bending and shear conditions. Results concerning a PT bridge deck are reported and the variability of the outcomes is discussed and compared with a reference case of “perfect knowledge”. The second purpose is to evaluate the sensitivity of resulting risk to a set of basic random variables that rule the chloride diffusion process and the subsequent rebars corrosion of a reinforced concrete bridge pier. The findings that degradation related uncertainties are significant, and some basic random variables are much more influential than others.