Corrosion Fatigue Behavior and Damage Mechanism of the Bridge Cable Structures

The long-term performance and corrosion fatigue damage status were investigated and analyzed under the service environment for the cable structures in cable-stayed bridges, suspension bridges, and suspender arch bridges. The artificial accelerated corrosion fatigue tests were carried out on galvanized parallel steel wire under coupled loading and environments. The damage mechanisms of galvanized parallel steel wire in corrosion, stress corrosion, and corrosion fatigue were investigated. The change laws of the mechanical properties of the cable were studied. Based on the image gray analysis, the evaluation method was proposed for the technical status of the damaged cable. Furthermore, combined with the cable damage evolution model, the service life prediction method and assessment technology of cables based on damage safety are established

Machine learning-based prediction of compressive strength in circular FRP-confined concrete columns

This research aims to evaluate the compressive strength of FRP-confined columns using machine learning models. By systematically organizing codes and models proposed by various researchers, significant indicators influencing compressive strength have been identified. A comprehensive database comprising 366 samples, including both CFRP and GFRP, has been assembled. Based on this database, a machine learning model was developed to accurately predict compressive strength. A thorough evaluation was conducted, comparing models proposed by codes and researchers. Additionally, a detailed parameter analysis was performed using the XGBoost model. The findings highlight the importance of both code-based and researcher-proposed models in enhancing our understanding of compressive strength. However, certain models show tendencies towards conservative or overestimated predictions, indicating the need for further accuracy enhancement. Among the models considered, the XGBoost model demonstrated the highest goodness of fit (0.97) and the lowest coefficient of variation (8%), making it a suitable choice for investigating compressive strength. Notable parameters significantly influencing compressive strength include FRP thickness, elastic modulus, and concrete strength

An experimental study of cathodic protection for chloride contaminated reinforced concrete

Cathodic protection (CP) is being increasingly used on reinforced concrete structures to protect steel reinforcing bars from corrosion in aggressive conditions. Due to the complexity of environmental conditions, the design specifications in national and international standards are still open to discussion to achieve both sufficient and efficient protection for reinforced concrete structures in engineering practices. This paper reports an experimental research to investigate the influence of chloride content on concrete resistivity, rebar corrosion rate and the performance of CP operation using different current densities. It aims to understand the correlation between the chloride content and concrete resistivity together with the CP current requirement, and to investigate the precision of the CP design criteria in standards

Experiment on Corrosion Fatigue Life of Steel Strands under the Coupling Effects of Chloride Environment and Alternating Loads

Corrosion pits will lead to local stress concentration on the surface of steel strands and even shorter fatigue life and worse mechanical properties of steel strands. In order to explore the corrosion mechanics of steel strands to predict the fatigue life, accelerated salt spray corrosion test is carried out to simulate the corrosion laws of steel strands and record the changes of the corrosion degrees during the experiment, considering the coupling effects of alternating loads and chloride environment. Besides, the impact of stress amplitudes on the corrosion degrees of steel strands is quantitatively studied by the corrosion weight loss, and corroded steel strands in experiment are graded according to the corrosion weight loss to test the mechanical properties, respectively; the results show that the corrosion weight loss and tensile strength of steel strands obey the exponential distribution, and the relationship with elongation is linear. In addition, the relationships between the stress concentration coefficient and the pit length, width, and depth are obtained; with the three-dimensional linear regression theory, the accuracy of the regression model is verified by t-value test, laying a foundation for predicting the corrosion life of the cables

Analysis of Corrosion-Fatigue Damage and Fracture Mechanism of In-Service Bridge Cables/Hangers

Cables/hangers are important load-bearing components of suspension, cable-stayed, and through-arch bridges. Their reliability throughout their service life directly affects the safety of these bridges. In this study, to provide a reference for the design, maintenance, and inspection of bridge cables/hangers, their damage and failure mechanisms were theoretically analyzed using finite element analysis and corrosion-fatigue simulation tests of steel wires, based on the characteristics of the cable/hanger damage. The finite element analysis showed that a rotation of 0.00113 rad in the lower anchorage area results in a bending stress of 18.8 MPa, indicating that the effect of the bending stress on the steel wires in this area cannot be neglected, as it is a factor contributing to the failure of long cables/hangers. We further used a salt spray chamber to simulate an acid-rain environment. The results showed the following: (1) corrosion-fatigue damage of the cables/hangers occurs under the combined action of a corrosive environment and an alternating stress. This leads to an intensified corrosion damage, reduced ductility, increased brittleness, and eventually, brittle fracturing of the cables/hangers. (2) In the same corrosive environment, the highest degree of specimen corrosion occurred during alternating stress, followed by static stress, and no stress. (3) After corrosion-fatigue damage occurred for a specimen, its breaking stress was about 60% in comparison to the uncorroded specimen. The percentage elongation at the break also decreased; this was about 40% in comparison to the uncorroded specimen, indicating brittle fracturing. (4) The steel wires of the cables/hangers with corrosion-fatigue damage are more prone to brittle fracture if they are exposed to complex spatial stresses

Test Study of the Bridge Cable Corrosion Protection Mechanism Based on Impressed Current Cathodic Protection

The cable system is an important bearing element of a bridge with stay cables or slings and a matter of major concern in the safety of the bridge structure. Bridge cables are vulnerable to corrosion induced by leakage and soaking during their service life. To solve this problem, and based on the idea of proactive control by means of the impressed current cathodic protection (ICCP) of bridge cables, this study designs and develops an ICCP system device for bridge cable protection. In this study, an accelerated corrosion test was conducted to test the ICCP system of steel wires inside the cables and the cables under acid rain conditions. The corrosion protection behavior of ICCP was analyzed to reveal the corrosion protection mechanism of bridge cable ICCP. The results show that in the cable ICCP system, the impressed current generated by a more negative voltage may improve the efficiency of corrosion protection, but an excessively negative voltage may cause hydrogen embrittlement of the cable steel wire due to overprotection. The rational range of −1.13 V to −1.15 V was set as the result of the overall consideration. Within this range, the cable is subject to the joint protection of ICCP and sacrificial anode cathodic protection (SACP). Corrosive products can delay the development of cable corrosion to a certain degree; the SACP protection efficiency of the galvanized coat reduces gradually with corrosion development; and cable ICCP protection efficiency increases gradually. The ICCP for cable corrosion protection is transformed from joint protection using both a sacrificial anode and impressed current into protection, mainly using an impressed current

Numerical and Experimental Identification of Seven-Wire Strand Tensions Using Scale Energy Entropy Spectra of Ultrasonic Guided Waves

Accurate identification of tension in multiwire strands is a key issue to ensure structural safety and durability of prestressed concrete structures, cable-stayed bridges, and hoist elevators. This paper proposes a method to identify strand tensions based on scale energy entropy spectra of ultrasonic guided waves (UGWs). A numerical method was first developed to simulate UGW propagation in a seven-wire strand, employing the wavelet transform to extract UGW time-frequency energy distributions for different loadings. Mode separation and frequency band loss of L(0,1) were then found for increasing tension, and UGW scale energy entropy spectra were extracted to establish a tension identification index. A good linear relationship was found between the proposed identification index and tensile force, and effects of propagation distance and propagation path were analyzed. Finally, UGWs propagation was examined experimentally for a long seven-wire strand to investigate attenuation and long distance propagation. Numerical and experimental results verified that the proposed method not only can effectively identify strand tensions but can also adapt to long distance tests for practical engineering

Numerical and Experimental Identification of Seven-Wire Strand Tensions Using Scale Energy Entropy Spectra of Ultrasonic Guided Waves

Accurate identification of tension in multiwire strands is a key issue to ensure structural safety and durability of prestressed concrete structures, cable-stayed bridges, and hoist elevators. This paper proposes a method to identify strand tensions based on scale energy entropy spectra of ultrasonic guided waves (UGWs). A numerical method was first developed to simulate UGW propagation in a seven-wire strand, employing the wavelet transform to extract UGW time-frequency energy distributions for different loadings. Mode separation and frequency band loss of L(0,1) were then found for increasing tension, and UGW scale energy entropy spectra were extracted to establish a tension identification index. A good linear relationship was found between the proposed identification index and tensile force, and effects of propagation distance and propagation path were analyzed. Finally, UGWs propagation was examined experimentally for a long seven-wire strand to investigate attenuation and long distance propagation. Numerical and experimental results verified that the proposed method not only can effectively identify strand tensions but can also adapt to long distance tests for practical engineering

Experimental Study and Numerical Analysis of Structural Performance of CRTS II Slab Track under Extreme High Temperature

A ballastless track is susceptible to damage and even failure of structural components under the long-term effects of extremely high temperatures. In this paper, considering the influence of different constraint boundaries, a 1 : 4 scaled model of a ballastless track-bridge structural system was produced and placed in a large-sized environmental chamber. The thermal performance of the track structure was studied by carrying out temperature loading tests at extreme temperatures. In combination with the scaled-down model test data, a 3D nonlinear finite element model was established to investigate the damage evolution of broad-narrow joints under temperature gradient loading. The results are shown as follows: (1) the cement asphalt (CA) mortar layer has a hysteretic effect on the vertical temperature transfer. The most unfavorable structural part is between the track slab and the CA mortar layer of the track structure. (2) The constraint conditions accelerate the rate of temperature transfer, creating disturbances to the internal stresses of the track structure and amplifying the internal stresses induced by the environmental temperature increase. (3) Temperature and longitudinal stresses in the track’s structural layers are highly correlated. There is a significant quadratic regression between internal temperature and structural stresses in different extreme high-temperature environments. (4) As the temperature gradient load increases, the damage occurs at the junction of the broad-narrow joint and tends to expand towards the ends, which has little effect on the compression damage of the broad-narrow joint but significantly increases the tension damage. The research could provide useful guidance for the scientific operation and maintenance of the ballastless track in extreme high-temperature environments

Research on the Artificial Acceleration Test System of Combined Environment and Loading Effect for the Bridge Structure

The bridges will be in service in a complex environment for over 100 years under the increasing traffic loading. So the long-term performance determines their safety and durability. Limited by the test condition and ability, present researches are mostly focused on the natural environment exposure tests and artificial environment acceleration tests for materials and components. According to the service conditions and load characteristics of the bridges, the accelerated test system was developed for bridge structure under combined environment and loading. This test system consists of three parts, including a large environment box, loading system and monitoring system. The environment box is 32 m long, 4 m wide and 3/10 m high. It is divided into 5 working bins which can be used alone or in combination. The simulation environment includes high temperature drying, low temperature freezing and thawing, damp cold, high temperature cycle, salt fog, rain, carbonation, temperature and humidity alternating and optical spectrum light aging environment. The servo static and dynamic loading system adopts Servotest actuators with loading tonnage from 400 tons to 50 tons. And the total tonnage is 1200 tons. Aided by the prestressed concrete reaction wall, steel structure frames and the anchor system, the external loading system can exert dynamic and static loads on the bridge structure in the environment box. And the non-contact nondestructive monitoring system can real-time monitor and measure their long-term deformation, internal force, cracking and other damage. This artificial acceleration test system can support the Chinese Long Term Bridge Program, and improve the safety, durability, reliability and long service life of bridges and other civil engineering