Residual capacity of fatigue-prone reinforced concrete structures

Designing reinforced concrete structures susceptible to fatigue damage requires satisfying the fatigue limit state. Current codes' stress-life curve considerations are confined to the design stages and cannot be used to monitor evolving fatigue damage if the structure in service is subjected to severe environmental conditions or loads that are higher than the design values. One significant observation in the area of fatigue damage is the scatter in results from various stress- life models. In addition, the use of S-N curves in areas of high local stresses exceeding stress-life curve limits does not necessarily mean global failure, especially if the structural stability is not affected. Reports on collapsed wind turbines due to foundation failure often indicate wind farm shutdown periods to enable investigations. The lack of means to study damage evolution or observe residual capacity of such reinforced concrete structures often results in the recommendation to rehabilitate all the foundations in most cases; hence, incurring significant losses. This report proposes an innovative approach that utilizes finite element analysis framework to predict the damage evolution and the residual capacity of reinforced concrete structures after a given number of fatigue loading cycles. The advantage of this approach stems from the fact that recorded wind loads and cycles from wind turbines can be read into the algorithm and the variations in loading amplitudes are considered in the analyses. To verify the model's reliability, fatigue life and residual capacity estimations are conducted on reinforced concrete specimens that were tested under fatigue loading. The results obtained portrayed substantial correlation.