چكيده به لاتين
Corrosion is one of the crucial damages that may occur to reinforced concrete structures. It also may affect the expected performance of the structure during the possible earthquakes. Onshore reinforced structures, bridges exposed to deicing salts in winter and also the pillars of marine structures under tidal waves, all of which are examples of corrosion damages. Corrosion mostly occurs due to two main reasons: chloride and carbonation which cause pitting corrosion and uniform corrosion, respectively. Corrosion starts with reaching of those two ions to the bar surface, passing by the physical and chemical passive covers. Corrosion also affects the mechanical properties of the steel and the concrete and reduces the seismic performance of the structure. In the present study, the chloride-based corrosion is considered. Moreover, a 20-storey moment frame concrete structure is investigated for seismic performance studies. At first, corrosion initiation time is determined by deterministic and probabilistic Monte-Carlo methods considering the uncertainties in the effective parameters for three water to cement ratios of 0.4, 0.45 and 0.5. Next, the effects of the corrosion such as cross section thinning and mechanical properties degradation of armatures and also reduction of compressive strength of concrete for the abovementioned water/cement ratios were exerted on under corrosion-damaged columns. The aforementioned studies, were discussed by using non-linear static and Incremental dynamic analyses combined with the seismic performance fragility curves. in regard to the conducted studies, the corrosion rate in the beginning of the corrosion is high and reduces in the next years. According to the results, the ductility of the structure is affected by the corrosion and will decrease due to it. In the end of the structure’s life span, the ductility reduces more than 72 and 39 percent for 0.5 and 0.4 water/cement ratios, respectively. By increasing the water/cement ratio, i.e. increasing the permeability, the reduction rate in the ductility rises significantly. This results and comparisons show that the water/cement ratio should be in a great concern for designs and constructions in on-shore structures. Furthermore, with changing the water/cement ratio from 0.4 to 0.5, in the end of the life span, the possibility of the exposure of the structure against great damages and even collapse in design earthquake magnitude and the biggest possible earthquakes rise considerably. At 0.5 water/cement ratio and the last 10 years of the structures life duration, a big bounce in the possibility of collapse is observed. In this period, the structure experience the biggest possible earthquakes risk because of the corrosion effects. Parameters such as concrete material, concrete quality and concrete cover on the bars, have a significant rule in decreasing the corrosion damages on the structure. The present study proves the importance of water to cement ratio in structures which may be affected by corrosion.
