Seismic Assessment of Bridges Including the Interaction Between Seismic Hazard and Deterioration Phenomena

Corrosion represents the most relevant deterioration phenomenon affecting reinforced concrete (RC) bridges all over the world. Given the complex, multivariate nature of the problem, the analysis of deteriorating RC bridges requires a multidisciplinary approach. Corrosion-induced deterioration is in fact associated with a number of effects, such as reinforcement section reduction, modification of steel and concrete mechanical properties, cover concrete cracking and spalling, increased rebar buckling effects, loss of bond strength and possible shift of failure mode. Seismic assessment of bridge structures is currently carried out according to the principles of Performance Based Earthquake Engineering (PBEE). The structural performance is expressed in terms of specific Decision Variables (DV). The PBEE framework represents a rational and rigorous tool for the seismic assessment of structures, allowing the analyst to explicitly take into account uncertainties in seismic hazard, structural response, fragility analysis and loss estimation. It is clear that the presence of deterioration phenomena leads to modification of structural properties and of the outputs of the framework. The integration of PBEE principles in lifetime seismic assessment is possible thanks to the modular nature of the former, allowing for including RC members deterioration in the process. In this thesis, the phenomenon of corrosion is first introduced through a systematic literature review, summarizing the research efforts carried out in the past years and identifying research gaps. An application of state-of-the-art approaches on the seismic risk assessment of a deteriorating case study bridge presenting evidence of carbonation-induced corrosion is then proposed. The case study is analyzed both in pristine and corroded conditions in three ideal sites representative of low, moderate and high seismic hazard. Validation of the corrosion scenario is obtained through comparison with experimental data and seismic reliability is quantified through the PBEE framework. The complex nature of modeling corrosion effects on the cyclic response of RC columns is subsequently addressed through the development of an efficient and refined fiber-based modeling strategy, including critical factors such as reinforcement area reduction, decreased strength and ductility of steel and concrete, inelastic buckling, low-cycle fatigue and diminished bonding performance. Model validation is obtained through comparison with experimental data. Additional investigations include comparison with a less refined approach in both quasi-static and dynamic conditions. The issue of cover cracking on corrosion development is then discussed, specializing the problem to explicitly include the interaction between environmental and seismic hazard in the analysis. The implications of concrete cracking are investigated both on durability and lifetime seismic performance assessment through probabilistic approaches. Given that the concept of Seismic Resilience represents the synthesis of modern PBEE, a specific framework tailored for deteriorating RC bridges is developed. Emphasis is placed on the effects of assumptions related to recovery phase uncertainty and time-varying initial functionality. The applicability of the approach is demonstrated through application to new and existing bridge configurations. Finally, an application of the principles of Direct Displacement Based Assessment (DDBA) to lifetime seismic analysis is proposed, aiming at reducing the computational burden of the analysis. State-of-the-art approaches for simplified seismic analysis are collected and integrated into the PBEE framework. Different structural configurations and exposure conditions are analyzed, and the results are compared to those obtained through Non-Linear Time History Analysis (NLTHA). An application to uncertainty analysis is then presented and the results are discussed in terms of risk metrics.