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The metal magnetic memory is used to detect the micro damage of structure based on the SMFL (self-magnetic flux leakage) effect, but it lacks an effective comprehensive diagnosis index suitable for...

A method to evaluate the mechanical performance of the corroded steel cable based on the strength condition is proposed. The corrosion safety factor (nα) was introduced, and the evaluation model was established. The eccentric effect as a result of the local corrosion was also considered. Then, the axial tensile experiment on steel-strand specimens was carried out. Furthermore, the mechanical properties, including the ultimate bearing capacity and limited strain, were analyzed. The results show that the properties of locally corroded specimens deteriorate more than uniformly corroded specimens. It is verified that the experimental data are in good agreement with the proposed theoretical model when the corrosion degree α is less than 0.35. Based on the experimental data and the related specification of the stayed cable, the relationship between nα and α was precisely determined. Besides, the level of nα or the safety redundancy can be characterized by the evaluation score δ. The lower the score δ, the less safe is the cable structure. This method also provides significant application prospects for safety evaluation research in civil engineering.

Aimed at the corrosion problem of the commonly used steel strand in the structure engineering, the Metal Magnetic Memory (MMM) was adopted as the non-destructive detection method in this paper. Firstly, based on the magnetic dipole model, the theoretical equations of the Self-Magnetic Flux Leakage (SMFL) for the trapezoidal corrosion section were derived, and the trend of the SMFL was depicted by the software of MATLAB. Then, the experiment of the corrosion detection for the unstressed steel strand based on the MMM was carried out. Ultimately, combined with the above theoretical model, the experimental data were analyzed. The results show that the corrosion of steel material can be relatively precisely calculated by the Faraday's first law of electrolysis. Via the horizontal scanning, the length of the corrosion region can be effectively obtained by the intersections of the x-Bx curves, and the theoretical model is verified. And via the vertical scanning, the inverse point x-z curve presents an inverted U-shape for the corroded steel strand and becomes a new means to determine the range of the corrosion areas. The findings have extensive prospects for the non-destructive detection in civil engineering.

The corrosion and cross-sectional loss of steel wires inside cable structures seriously threaten the operational safety of bridges. In the present study, a probability evaluation method for the cable corrosion degree was proposed in association with the Bayesian model. Firstly, the evaluation index ‘X’ was expressed based on the magnetic dipole model of self-magnetic flux leakage (SMFL), and corrosion detection experiments were carried out on both steel strands and wires. Then, the distributions of the measured SMFL signals were analyzed. The statistical law between ‘X’ and the cross-sectional loss ratio ‘α’ was depicted and revealed based on the experimental data. Finally, the positive correlation between ‘X’ and ‘α’ was quantified by four different levels, in turn, the evaluation criteria for the corrosion degree of cable structures were obtained. Via the comparative analysis with the different prior probability distribution of corrosion degree, the reliability of the evaluation criteria was verified.

To detect the hidden defects of ferromagnetic components, it is crucial to first locate the position of defects. In this paper, the three-dimensional magnetic dipole model of a solid columnar structure with a sector cube defect was built to theoretically explain the self-magnetic flux leakage effect of the bridge-stayed cable. The uniform or linear distribution of charge density on specific defect planes was considered in the model. Then, an experimental study on the defective steel strand cable specimens under different corrosion degrees was carried out. The results show that the corrosion accelerates the variation of magnetic signal Bz near the corrosion region, and the phenomenon is consistent with the theoretical model. Moreover, the relationship between the normalized signal Bznor and the corrosion factor αφ reveals the influence of the corrosion defect on the magnetic signal intensity in different detection positions, demonstrating the three-order polynomial growth trend. Combined with the axial and the circumferential scanning, the spatial location method of the corrosion defect was proposed for the detection of the bridge-stayed cable.

This paper presents a nondestructive test method to evaluate the residual bending strength of corroded reinforced concrete beam by analyzing the self-magnetic flux leakage (SMFL) signals. The automatic scanning device was equipped with a micromagnetic sensor and sensor-based experimental details were introduced. Next, the theoretical formula of the normal component HS(z) of the SMFL signal that originated from the corroded region was derived based on the magnetic dipole model and the experimental results were discussed. The results indicate that the experimental data of HS(z) are consistent with the theoretical calculations, both location and extent of the steel bars corrosion can be qualitatively determined by using HS(z). The gradient K of HS(z) is approximately linearly related to the loss rate, S, of the bending strength, which can be used to evaluate the residual bending strength of the corroded reinforced concrete beam. This work lays the foundation for evaluating the residual bending strength of corroded reinforced concrete beams using the SMFL signal, the micromagnetic sensor is further applied to the civil engineering.

This paper presents a non-destructive test method for steel corrosion in reinforced concrete bridges by using a 3-dimensional digital micro-magnetic sensor to detect and analyze the self-magnetic field leakage from corroded reinforced concrete. The setup of the magnetic scanning device and the measurement mode of the micro-magnetic sensor are introduced. The numerical analysis model is also built based on the linear magnetic charge theory. Compared to the self-magnetic field leakage data obtained from magnetic sensor-based measurement and numerical calculation, it is shown that the curves of tangential magnetic field at different lift-off height all intersect near the edge of the steel corrosion zone. The result indicates that the intersection of magnetic field curves can be used to detect and evaluate the range of the inner steel corrosion in engineering structures. The findings of this work propose a new and effective non-destructive test method for steel corrosion, and therefore enlarge the application of the micro-magnetic sensor.

This paper proposed a new computing method to quantitatively and non-destructively determine the corrosion of steel strands by analyzing the self-magnetic flux leakage (SMFL) signals from them. The magnetic dipole model and three growth models (Logistic model, Exponential model, and Linear model) were proposed to theoretically analyze the characteristic value of SMFL. Then, the experimental study on the corrosion detection by the magnetic sensor was carried out. The setup of the magnetic scanning device and signal collection method were also introduced. The results show that the Logistic Growth model is verified as the optimal model for calculating the magnetic field with good fitting effects. Combined with the experimental data analysis, the amplitudes of the calculated values (BxL(x,z) curves) agree with the measured values in general. This method provides significant application prospects for the evaluation of the corrosion and the residual bearing capacity of steel strand.

Aimed at the health monitoring and evaluation of bridges based on sensing technology, the monitoring contents of different structural types of long-span bridges were defined. Then, the definition, classification, selection principle, and installation requirements of the sensors were summarized. The concept was proposed that new adaptable long-life sensors could be developed by new theories and new effects. The principle and methods to select controlled sections and optimize the layout design of measuring points were illustrated. The functional requirements were elaborated on about the acquisition, transmission, processing, and management of sensing information. Some advanced concepts about the method of bridge safety evaluation were demonstrated and technology bottlenecks in the current safety evaluation were also put forward. Ultimately, combined with engineering practices, an application was carried out. The results showed that new, intelligent, and reliable sensor technology would be one of the main future development directions in the long-span bridge health monitoring and evaluation field. Also, it was imperative to optimize the design of the health monitoring system and realize its standardization. Moreover, it is a heavy responsibility to explore new thoughts and new concepts regarding practical bridge safety and evaluation technology.