ABSTRACT
Numerous bridges all over the world are suffering from deterioration problems, which entail massive loss of life and property. To protect concrete structures from environmental hazards, efforts should be made on all designing, construction and maintenance stages, in other words, through the entire lifecycle. Obviously, rational description of the lifecycle performance is the start point to achieve this goal. Lifetime reliability analysis of simple bridge structures has been published by Akgül and Frangopol (2004), Darmawan and Steward (2007), Czarnecki and Nowak (2008) etc. However, works on deterioration analysis of complex structure system is relatively rare in recent literature. Reliability computation of components in large structure systems is hard to perform due to the implicit limit state function, large number of random variables and complicated deterioration process. Nonetheless, since durability problems are frequently exposed on long-span bridges, research on the deterioration analysis of complex structural system needs more attention.
Generally, newly built structures will experience the similar degrading process. Firstly, when protection system fails due to environmental erosion and material degradation, main structural parts begin to deteriorate. This state can be defined as the Protection Failure Limit State (PFLS). Secondly, when local damages accumulate to certain level, structural safety and usability will be jeopardized. The corresponding limit state is Local Damage Limit State (LDLS). Finally, durability problem can lead to loss of load bearing capacity. If load effect exceeds the capacity, failure will happen. The limit state when sectional resistance equals load effect is defined as Ultimate Limit State (ULS).
Chloride-induced corrosion is researched in detail. Corrosion of steel in concrete is usually triggered by the failure of passivation film. When the content of chloride ions reaches certain level, passivation film will be decomposed. The diffusion of chloride ions is modeled by Fick’s law, which is solved using FE method. Corrosion initiation is triggered when chloride ions concentration exceeds threshold value and corrosion propagation is modeled based on corrosion current density.
A long-span cable-stayed bridge is chosen as an illustrative example. Deterioration analysis and reliability calculation are performed for the concrete main beam. Results show that local problems such as protection failure and local damage are remarkable while resistance degradation is relatively insignificant.
