Time-Dependent Failure Possibility Analysis of Reinforced Concrete Structures

Abstract

Structural performance depends on the design, construction, environment, utilization, and reliability aspects. From these, other factors can be controlled by adopting proper design and construction techniques, but the environmental factors are difficult to control. Hence, the environmental factors in the analysis and design are mostly not considered sufficient in practice; however, they have significant effects on the performance of the structures in the design life. It is in this light that this study aimed at performing the time-dependent safety and serviceability performance analysis of reinforced concrete structures majorly considering environmental factors such as creep, shrinkage, and corrosion that possess uncertainty. To achieve the desired objective, a simply supported reinforced concrete beam was designed and detailed to Eurocode (EC2). Different design parameters such as corrosion parameters, creep and shrinkage, the time-dependent properties of the material have been identified and modeled through a thorough literature review. The empirical equations provided in design codes were modified to consider the time-variant parameters in time-dependent performance analysis. In the presence of uncertainty of parameters, it is impossible to obtain the absolute reliability of the structure. The sources of uncertainties in reinforced concrete are the randomness of variables, mathematical models, physical models, environmental factors, and gross error. Uncertainties broadly classified as aleatory and epistemic uncertainties. This research mainly addressed the epistemic uncertainty of reinforced concrete structure to handle the imprecise data using fuzzy concepts. The fuzziness of variables identified and their membership functions were generated by MATLAB R2018a using the heuristic method. In addition to the identification of fuzziness of variables, the study further extended to design optimization and performance level evaluation of reinforced concrete structure using fuzzy relation and fuzzy composition to explore the application of fuzzy concepts. In the design of reinforced concrete structure using fuzzy relation and composition methods, the design is taken as optimum when the performance degree of membership tends to unity. Failure possibility is a measure of safety when a structure encounters with fuzzy uncertainties. If uncertainties are time-dependent, the possibility of performance under zero results in time-dependent failure possibility, and it becomes more pronounced during improper consideration of environmental factors. Therefore, in this study, time-dependent parameters are taken into account for exploring the effects of environmental factors in reinforced concrete structures. Possible failure modes were identified and estimated using modified time-variant empirical equations to consider the propagation of input variables that are characterized by membership functions to output responses. Then, the time-dependent failure possibility is evaluated by the numerical optimization procedure. Real-time data has been collected from the city of Addis Ababa, Ethiopia for the case study to substantiate the methodology presented in this study. From the detailed modeling and analysis, considering the moderate corrosion rate with corresponding ambient temperature and relative humidity of the considered site, the structure safely performs for less than half of its design life.