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To obtain a precise finite-element model (FEM) for analyzing the dynamic response of corroded beams at high temperatures, a stepwise FEM modification strategy is proposed based on the improved extreme learning machine. Three concrete beams were designed and cast, and the dynamic response characteristics of corroded concrete beams at room temperature and high temperature are discussed. Firstly, electrical accelerated corrosion tests and vibration tests were conducted on simply supported beams at room temperature. The fundamental frequencies of concrete beams under different corrosion ratios were measured. The attenuation law of fundamental frequency with corrosion ratio also was studied. Subsequently, the FEM under different corrosion ratios was modified. The bond-slip between steel bars and concrete under different degrees of corrosion was considered during the correction process. Finally, a vibration test at high temperature was performed. The modal attenuation law of corroded beams at high temperatures was analyzed. Based on the modified FEM, numerical analysis at high temperature was performed. The proposed FEM modification strategy and the study of the attenuation regularities of modal information under fire exposure provide a foundation for further research on the damage development of corroded reinforced concrete (RC) beams under fire exposure. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that elevated temperatures exert a significant influence on the structural performance of reinforced concrete (RC) members. However, the residual shear performance of the RC beam under the combined effects of stirrup corrosion and fire has not been thoroughly explored. Therefore, this paper aims to investigate this aspect by prefabricating eight RC beams and employing experimental, numerical, and theoretical methods. The influence of varying stirrup corrosion degrees and fire exposure time on the residual shear capacity of these beams was examined. It was observed that corrosion-induced cracks had an impact on the distribution of the temperature field within the RC beams. Furthermore, the exposure to the corrosion–fire combination significantly affected the shear capacity of the RC beams. Notably, stirrup corrosion may lead to a more brittle failure after a fire. To assess the impact of corrosion degree and fire exposure time on the temperature field and residual shear properties of RC beams, a simplified finite element (FE) model considering the effect of concrete spalling was developed. The accuracy of this model was validated through a comparison with experimental results. Finally, three theoretical methods for predicting the residual shear capacity of postfire RC beams with corroded stirrups were proposed, based on Chinese, American, and European codes. A comparison between the calculated and test results revealed a good agreement. These methods can provide conservative predictions for practical engineering applications. [ABSTRACT FROM AUTHOR]

This paper introduces an enhanced you only look once (YOLO) v5s‐D network customized for detecting various categories of damage to post‐fire reinforced concrete (RC) components. These damage types encompass surface soot, cracks, concrete spalling, and rebar exposure. A dataset containing 1536 images depicting damaged RC components was compiled. By integrating ShuffleNet, adaptive attention mechanisms, and a feature enhancement module, the capability of the network for multi‐scale feature extraction in complex backgrounds was improved, alongside a reduction in model parameters. Consequently, YOLOv5s‐D achieved a detection accuracy of 93%, marking an 11% enhancement over the baseline YOLOv5s network. Comparison and ablation tests conducted on different modules, varying dataset sizes, against other state‐of‐the‐art networks, and on public datasets validate the resilience, superiority, and generalization capability of YOLOv5s‐D. Finally, an application leveraging YOLOv5s‐D was developed and integrated into a mobile device to facilitate real‐time detection of post‐fire damaged RC components. This application can integrate diverse fire scenarios and data types, expanding its scope in future. The proposed detection method compensates for the subjective limitations of manual inspections, providing a reference for damage assessment. [ABSTRACT FROM AUTHOR]

Bond failure is a crucial element in ascertaining the failure mechanisms of reinforced concrete (RC) structures. The investigation pertaining to the dynamic loading's impact on bond efficacy remains a lacuna within scholarly discourse. Therefore, 138 eccentric pull-out half-beam specimens have been fabricated to probe the intricate degradation mechanisms underlying the bond-slip phenomena between concrete and reinforcement when subjected to high-temperature transients. Initially, a series of experiments were conducted on half-beam specimens possessing different reinforcement diameters and embedded lengths. Subsequently, the transient temperature changes within the bond segment were recorded, and this was pursued by the execution of eccentric pull-out tests. Second, the bond stress-strain curves under transient temperature were measured. The experimental findings revealed that the bond strength peaked at 101°C and showed an upward trend up to 302°C. Beyond this temperature, however, the bond strength exhibited a decline. Specifically, at a target temperature of 400°C, the bond strength increased by 18.1% and 9.3% compared to values at 20°C and 200°C, respectively. In contrast, it decreased by 23.2% and 41.3% in comparison to values at 600°C and 800°C. Additionally, as the reinforcement diameter increased, there was a decrease in bond strength, while the ultimate failure force increased. Finally, a methodology for evaluating bond strength under dynamic temperature was introduced, and a semiempirical constitutive model was formulated, taking into account the interplay between different heating rates. The constitutive model underwent validation through temperature computations, proposing a bending moment calculated methods, thus affirming its accuracy under fluctuating temperature scenarios. [ABSTRACT FROM AUTHOR]

The fire resistance of corroded reinforced concrete has attracted extensive attention, mainly due to the frequent occurrence of fires in old structures. However, using the postfire bond strength to predict structural capacity during fires leads to inaccurate results. Thus, in this study, an accelerated corrosion test and an eccentric pullout test were performed under steady-state conditions from 20°C to 800°C. The test results indicated that compared with the bond strength at 20°C, the bond strength at 200°C decreased by 6% for the corroded specimen (corrosion level below 4.3%) and increased by 11% for the uncorroded specimen. When the temperature exceeded 500°C, the storage modulus and bond strength decreased 55%. Increasing the rebar diameter reduced the bond strength by approximately 29% and made the descending section of the τ-s curve steeper during exposure to fire. The energy dissipation at 100°C was larger than that at other temperatures, and the bond stiffness at 600°C was 12.5% of that at 20°C. The reduction in bond stiffness postponed the development of splitting cracks, restricted the crack width, and prevented splitting failure. Subsequently, temperatures dependence was analyzed and methods were proposed for the calculation of bond strengths at elevated temperatures. The results obtained with the proposed continuous bond-slip model were in satisfactory agreement with the pullout test results. Finally, the comparison of integral absolute error indicated that the model could be used to make accurate calculations of bond strengths during fires. [ABSTRACT FROM AUTHOR]

The bond performance of corroded reinforced concrete (RC) subjected to fire has a significant influence on evaluating the structural load-bearing capacity and early warning for structure collapse. However, the bond deterioration mechanism of corroded RC subjected to fire has not been sufficiently studied. Therefore, in this study, the bond behavior between corroded reinforcement and concrete at elevated temperatures was systematically investigated by testing 76 corroded specimens obtained by the accelerated corrosion method. Eccentric pull-out tests were performed immediately when the temperature at the interface of the reinforcement and concrete reached the target values. The main parameters include the degree of corrosion (i.e., 0%, 2%, 5%, 10%, and 20%), concrete cover thickness (20, 30, and 40 mm), and temperature (20°C, 100°C, 200°C, 400°C, 500°C, 600°C, and 800°C). The test results indicated that when exposed to temperatures below 400°C, the bond strength at elevated temperatures is less than that after natural cooling. The bond strength changed minimally at elevated temperatures between 200°C and 400°C, while a significant reduction was observed after natural cooling. Moreover, the bond strength increased by 8.7% at less than 3.4% corrosion degree. However, severe corrosion (with a corrosion degree exceeding 13.2%) and high temperature (exceeding 500°C) decreased the bond strength by 16.3% and 29.6%, respectively. In addition, methods for calculating the bond strength and residual bond strength based on the deterioration of concrete compressive strength at elevated temperatures are proposed. [ABSTRACT FROM AUTHOR]

The full-scale fire tests of three RC columns under axial load were carried out with standard heating curves. The immediate reactions and collapse states of tested columns were analyzed and the temperature distribution of sections and axial deformations were measured. The degradation of bearing capacity of RC columns was found mainly on the following respects : the degradation of concrete strength, the increase of axial deformations and the destructions of working performances. Computer simulation compiled by author was done using the finite element method. The numerical results agree well with test data. A simplified calculation formula is put forward for RC column bearing capacity under fire, which is proved to be reliable according to the comparisons between test record and calculation results. [ABSTRACT FROM AUTHOR]

• Molecular dynamics simulation is used to observe the microstructure of concrete and steel interface. • The relationship between interfacial bonding and mechanical properties is revealed. • Interfacial water changes the bonding properties of interfacial region, which reduces the strength of reinforced concrete. The interfacial region between concrete and steel reinforcement (SCI) determines strength and durability of reinforced concrete structure. In this work, the molecular dynamics simulations were employed for understanding the bonding mechanism of SCI region. In the interfacial region, the calcium ions play the mediation of bonding C S H surface and the passivation film by combing the oxygen atoms and hydroxyl groups of C S H in the nearest neighbors. The hydroxyl groups in the γ-FeOOH and the unbinding O atom in the C S H provide enough oxygen sites to form the hydrogen bonds and hydration, which also improve the bond strength of the interlayer region. Furthermore, introducing single-layer water results in the hydrated Ca2+-water cluster formation, weakening the Ca O connectivity between C S H and passive film. Double-layer water can significantly increase the diffusion of interfacial components and decrease the stability of interfacial bonds. In addition, simulated pull-out test and uniaxial tensile test were performed to evaluate bond strength of C S H and γ-FeOOH. Hydrolytic weakening is found due to water ingress in the interfacial region. Double-layer water penetration results in reduction of interfacial shear strength from 0.53 GPa to 0.38 GPa. Also, the Young's modulus and cohesive strength reduced by more than 50% percentage. This work is expected as an important reference for design and development of reinforced concrete in engineering application. [ABSTRACT FROM AUTHOR]