The technical condition of bridges has become a crucial issue for organizing the maintenance and repairs in bridge management systems. It is of great practical engineering significance to construct an effective model for predicting the technical condition degradation of the bridge through the use of the historical inspection data. Based on the semi-Markov random process, this paper proposes a useful deterioration prediction model for bridges in the highway network. From the historical inspection data of the prefabricated concrete box girder bridges, the degradation curves of technical condition rating are obtained. The effect of bridge length on degradation rate of the prefabricated concrete box girder bridges is analyzed. According to the Weibull distribution parameters of different condition grades, the technical state degradation models for a bridge group and an individual bridge are proposed to predict the performance of the overall bridge and superstructure of the bridge. The results show that with the increase in bridge length, the degradation rate of bridge technical condition increases. The degradation rate of the technical condition of the superstructure is faster than that of the overall bridge. The proposed semi-Markov stochastic degradation model for the bridge group can not only predict the different condition ratings of the bridges at any time, but also predict the future deterioration trend of an individual bridge under any ratings.

Due to the presence of stray current in the subway environment, the durability issues of subway structures differ from those of general structures. This study simulates the combined effects of chloride ions and stray current in the subway environment through electrochemical corrosion experiments, thereby analyzing the corrosion morphology and mechanical property degradation of steel strands and the corrosion-induced cracking of concrete. The experimental results indicate that stray current affects the strength and ductility of steel strands as well as the cracking of concrete. The corrosion difference coefficient μ_c at different positions is greater than 1.6 and the average corrosion degree η_ave is less than 7%. The corrosion morphology gradually changes from non-uniform to uniform corrosion until the η_ave is greater than 12%. The concrete crack width under a stray current of 60 mA is 10.67 times that of cracks under 20 mA after 42 days, which is approximately linearly related to the current intensity. Based on the experimental results, a corrosion-induced crack prediction model for prestressed concrete under stray current is proposed, with the main influencing factors being current intensity, concrete tensile strength, and protective layer thickness. These findings can provide valuable references for the durability analysis of subway structures.

To study the chloride transport properties of urban rail transit structures under the action of stray currents, electrochemical tests were employed as part of this paper to investigate the impact of stray currents on cementitious materials and pore structure and further analyze the chloride distribution of specimens in different conditions. Results show that a stray current accelerates calcium ion precipitation in chloride solutions, reducing calcium hydroxide content compared to unelectrified specimens. This dissolution alters the concrete pore structure, increasing porosity by 26.3%, 31.2%, and 36.1% for specimens electrified at 50 mA, 100 mA, and 150 mA, respectively, after 28 days. The effect coefficient k_p of stray currents on the porosity of concrete is given with the test results. Electrified specimens have a higher chloride content compared to unelectrified specimens, with free chloride increasing more than bound chloride as current and time increase. The chloride ion binding capacity of concrete electrified at 150 mA is only 60% that of unelectrified, indicating the significant weakening effect of stray currents on it.

To investigate the bonding performance of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) technique under different curing temperatures, a total of five test specimens strengthened with NSM CFRP strip were tested by direct pull-out methods. The strain of CFRP strip, interfacial bonding shear stress, ultimate load and failure mode were analyzed through the test. The experiment results showed that the ultimate load and bonding shear stress of the specimens increased gradually when curing temperature was lower than the glass transition temperature (T _g) of the bond material. Afterward, they gradually decreased with the increase in temperature. The bonding shear stress was gradually transmitted from the loading end to the free end. The failure modes were changed from CFRP strip–adhesive interface bonding failure to CFRP strips fracture failure with the temperature rising. In this paper, the bonding performance experiment results of NSM CFRP strip could provide a reference for the rapid strengthening of monorail traffic track beams.

To study the mechanical properties of asymmetric K-shaped square tubular joints with built-in stiffening rib lap joints, axial tensile tests were carried out on one K-shaped joint without built-in stiffening ribs and four K-shaped joints with built-in stiffening ribs using an electro-hydraulic servo structural testing system. The effects of the addition of stiffening ribs and the welding method of the stiffening ribs on the mechanical properties were studied comparatively. The failure mode of the K-shaped joint was obtained, and the strain distribution and peak displacement reaction force in the nodal region were analyzed. A finite element analysis of the K-shaped joint was carried out, and the finite element results were compared with the experimental results. The results showed that the addition of transverse reinforcement ribs and more complete welds shared the squeezing effect of the brace on the chord. Arranging more reinforcing ribs in the fittings makes the chord more uniformly stressed and absorbs more energy while increasing the flexural load capacity of the fittings’ side plates. The presence of a weld gives a short-lived temperature increase in the area around the crack, and the buckling of the structure causes the surface temperature in the buckling area to continue to increase for some time. The temperature change successfully localized where the structure was deforming and creating cracks. The addition of the reinforcing ribs resulted in a change in the deformation pattern of the model, and the difference occurred because the flexural capacity of the brace with the added reinforcing ribs was greater than that of the side plate buckling.