قابلیت اطمینان سازه های بتن آرمه در معرض خوردگی و فرسودگی و تغییرات اقلیمی Reliability of Reinforced Concrete Structures Subjected to Corrosion-Fatigue and Climate Change

1. Introduction Reinforced concrete (RC) civil infrastructure systems are critical assets for the socioeconomic development of any country. Designing and maintaining these systems for a particular service lifetime have been recognized as critical issues worldwide. RC structures are characterized by high durability; however, during their operational life, they are subjected to internal and external actions that affect performance, serviceability and safety (Imam et al. 2015; Kim et al. 2016; Marquez-Pen˜aranda et al. 2016; Morga and Marano 2015; Sa´nchez-Silva and Klutke 2016). Nowadays, many deteriorated structures are evaluated for possible repair and continued service because their replacement would be economically unfeasible. For example, about 173,000 bridges in the United States are structurally deficient or functionally obsolete due in part to corrosion (Bhide 1999; Pritzl et al. 2014; Radlin´ska et al. 2014). Regarding costs, Koch et al. (2016) reported that the global cost of corrosion is US$2.5 trillion (about 3.4% of the global Gross Domestic Product). Thus, developing robust models for prediction and strategies for periodic inspection and maintenance plays a significant role in enabling target reliabilities to be met over a period of continued service (Bastidas-Arteaga et al. 2009; Bastidas-Arteaga and Schoefs 2015; Clifton 1993; Mori and Ellingwood 1995). This paper focuses on a combined corrosion-fatigue deterioration mechanism. Corrosion is induced by chloride penetration that results in turn from a complex interaction between physical and chemical processes that are driven by environmental surrounding conditions (Bastidas-Arteaga and Stewart 2016; Nguyen et al. 2017; Saetta et al. 1993). Combined corrosion-fatigue deterioration results from the action of cycling stresses in corrosive environments. Localized corrosion leading to pitting may provide sites for fatigue crack initiation. For example, several experimental studies have shown that pitting corrosion has been responsible for the nucleation of fatigue cracks in a wide range of steels and aluminum alloys (Ahn et al. 1992; Chen and Duquette 1992; Kondo 1989). Corrosive agents (e.g., seawater) increase the fatigue crack growth rate (Gangloff 2005), whereas the morphology of metals/alloys at micro-level governs the pit nucleation sites (Rajasankar and Iyer 2006). There exists a limited amount of experimental tests on corrosion-fatigue in RC structures. Ahn and Reddy (2001) performed an experimental study to evaluate the durability of RC beams subjected to fatigue loading and chloride ingress. The tests included 16 beams and accounted for the influence of static and cyclic loading for different water/ cement ratios. Alternate filling and draining of a tank simulated the marine tidal zone, and a galvanostatic corrosion technique was used to accelerate corrosion of the reinforcement. The ultimate strength of the beams was tested after 78,000 cycles by applying four-point flexural loading.