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For a reinforced concrete beam subjected to fatigue loads, the structural stiffness and bearing capacity will gradually undergo irreversible degeneration, leading to damage. Moreover, there is an inherent relationship between the stiffness and bearing capacity degradation and fatigue damage. In this study, a series of fatigue tests are performed to examine the degradation law of the stiffness and bearing capacity. The results pertaining to the stiffness show that the stiffness degradation of a reinforced concrete beam exhibits a very clear monotonic decreasing "S" curve, i.e., the stiffness of the beam decreases significantly at the start of the fatigue loading, it undergoes a linear decline phase in the middle for a long loading period, and before the failure, the bearing capacity decreases drastically again. The relationship between the residual stiffness and residual bearing capacity is determined based on the assumption that the residual stiffness and residual bearing capacity depend on the same damage state, and then, the bearing capacity degradation model of the reinforced concrete beam is established based on the fatigue stiffness. Through the established model and under the premise of the known residual stiffness degradation law, the degradation law of the bearing capacity is determined by using at least one residual bearing capacity test data, for which the parameters of the stiffness degradation function are considered as material constants. The results of the bearing capacity show that the bearing capacity degradation of the reinforced concrete beam also exhibits a very clear monotonic decreasing "S" curve, which is consistent with the stiffness degradation process and in good agreement with the experiment. In this study, the stiffness and bearing capacity degradation expressions are used to quantitatively describe their occurrence in reinforced concrete beams. In particular, the expression of the bearing capacity degradation can mitigate numerous destructive tests and save cost. The stiffness and bearing capacity degradation expressions for a reinforced concrete beam can be used to predict the deformation and bearing capacity of a structure during the service process and determine the structural fatigue damage and degree of degradation. [ABSTRACT FROM AUTHOR]

• Bending strength of corroded RC beams evaluated via innovative NDT technique SMFL. • SMFL index K for quantitative evaluation was proposed theoretically. • Quantitative correlation between index K and bending strength loss rate β was established. • Bending strength of corroded RC beams was quantitatively evaluated via K based on Bayesian model. The self-magnetic flux leakage (SMFL), a non-destructive testing (NDT) technique, was applied innovatively to the quantitative statistical evaluation of the bending strengths of corroded reinforced concrete (RC) beams. In this study, the variations of the SMFL and bending strength caused by steel bar corrosion were analyzed theoretically and experimentally. Based on theoretical analysis, a SMFL index K that is not affected by the initial magnetization and magnetization history was proposed. The bending strength loss rate β of the corroded RC beams could be evaluated quantitatively using index K. 1775 K data from 18 corroded RC beams with different corrosion degrees were extracted, and the experimental correlation between K and β was established based on the experimental data and a theoretical correction. The results indicated that the magnitudes of K from different beams were similar, which proved that K eliminated the difference between the initial magnetization and magnetization history between different individuals. K and β were approximately exponentially related, and their correlation was not significantly affected by the stirrups. In view of the discreteness of the experimental sample K , β was statistically evaluated via K based on a Bayesian model. The posterior probability distribution of β in different value intervals when K was in a certain value interval was given. Thus, the quantitative classification of β was realized. This work is beneficial for the engineering evaluation of the bending strengths of corroded RC beams and provides an innovative research idea. [ABSTRACT FROM AUTHOR]

The non-destructive quantitative evaluation of the rebar corrosion degree is an urgent problem to be solved for corroded reinforced concrete structures. In this study, a non-destructive quantification method for the rebar localized corrosion cross-sectional area was proposed based on the dynamic linkage mechanism of the induced magnetic and self-magnetic flux leakage fields of rebar. As verified by data from the experiment and the finite element simulation, this quantification method could eliminate the adverse influence of the magnetic property differences of the rebar. The results indicated that different quantitative indices for corrosion evaluation could be created based on this method, and an index created by two transformations with the same geometric characteristics had better quantification capability. The four quantitative indices I 1 , I 2 , I 3 , and I 4 created in this study were all linearly related to the rebar localized corrosion cross-sectional area ratio S , and index I 3 had the relatively best quantitative capability and applicability. This quantification method provided an innovative solution for the non-destructive quantitative evaluation of rebar corrosion. • The dynamic linkage mechanism between the IM and SMFL fields of corroded rebar was demonstrated. • An SMFL-based non-destructive quantification method for the rebar corrosion degree was proposed. • Four quantitative indices were created based on this quantification method. • All of the created quantitative indices were linearly related to the corrosion cross-sectional area of rebar. [ABSTRACT FROM AUTHOR]