The reinforcement effect and durability of carbon fibre-reinforced polymer (CFRP) sheets are important indicators that affect its promotion and application. This study conducted an experimental investigation of the degradation behavior of reinforced concrete (RC) beams strengthened with CFRP. The RC beams were deteriorated under the compound effects of acid-salt mist and carbon dioxide for a time period t 1 i , then strengthened with one or two layers of CFRP sheets, and placed in the same deterioration environment for an additional time period t 2 i . The failure modes, load-deflection curves, rigidity, and flexural carrying capacity changes were studied after the deteriorated RC beams were loaded to failure. Three combinations of deterioration periods were considered in this study: different t 1 i and same t 2 i , same t 1 i and different t 2 i , and same total time ( t 1 i  +  t 2 i ). This study found that the U-shaped hoops and the side concrete peeled off gradually as the CFRP-strengthened RC beams were deteriorated again with time. Under the ultimate load, the strengthening layer in the tension zone stripped. The strengthened layer, which consisted of CFRP, a binder, and the concrete cover, was stripped from the RC beam during loading. The deflection of the strengthened layer behaved differently from the other part; this disharmony prevented the mobilization of the tensile advantage of CFRP. The mechanism of RC beam’s mechanical behaviour was analyzed in terms of the degrees of deterioration of RC beams and CFRP and their coupled effects. The conclusions of this study can be used as references in the prediction of strength changing and service life of strengthened RC beams.

With the continuous progress of the construction industry, the requirements for concrete in the bridge engineering are getting higher and higher. This research mainly discusses the detection of D-shaped concrete-filled steel tube structure in bridge engineering. In this study, the D-shaped concrete-filled steel tube member was used as the research object, and the load-displacement curve of the D-shaped concrete-filled steel tube compression-bending member was analyzed by the fiber model program. In the determination of the bonding state of the concrete-filled steel tube interface, in order to avoid the impact of mechanical and manual vibrating and the difference in concrete pouring methods on the test, the study uses C60 self-compacting microexpansion concrete. While pouring the specimens, three sets of cube specimens with a side length of 100 mm are reserved to determine the mechanical properties of the concrete simultaneously. In the temperature shock measurement of the concrete-filled steel tube specimen, the concrete-filled steel tube specimen was placed in a resistance heater during the simulated heating stage and heated to 20°C, 40°C, 60°C, and 80°C at room temperature. When measuring the mechanical properties of the specimen under the axial load, the specimen is heated from room temperature to the temperature of the entire section to reach 20°C, 40°C, 60°C, and 80°C. After preloading, the load of each level is 10t for continuous operation. Load and record the strain of the steel pipe and concrete under each load. If only the radial effect of the steel tube on concrete is considered, the temperature of 11°C, 20°C, and 80°C is the best ambient temperature. The results show that the D-shaped steel tube concrete interface state can provide a certain theoretical and experimental reference for the optimization of the steel tube concrete interface, ensuring the long-term working performance of the steel tube concrete under the harsh environment.

Seismic actions inevitably cause cyclic plastic deformations in steel frame connections, which is a common cause of failure in steel structures. Nonlinear finite element (FE) static analysis has been employed in the study of the cyclic plastic behavior of a T-stub connection based on the reported cyclic test on the corresponding extensively tested T-stub connection made of Q235 steel. In particular, the isotropic-hardening and Chaboche constitutive models were employed to predict both the stress distribution and plastic development on the T-stub and the hysteretic curves of the entire T-stub connection. The two constitutive models were calibrated by four material tests to describe the yield and hardening behaviors of the Q235 steel used to make this T-stub connection. The two sets of simulation results obtained from the simulations of the two FE models employed by the two different constitutive models were compared with each other and with the experimental results. The comparisons reveal that the simulation results are similar and in good agreement with the experimental results when the cumulative plastic deformation in the T-stub is small. However, the results of the FE analysis using the Chaboche model are in better agreement with the experimental results when the cumulative deformation in the T-sub is large. This study can provide a reference for FE simulation of the cyclic plastic behavior of steel connections, including the T-stub connection.

This study introduced gas control technology in goaf using adjacent roadway large-diameter (550 mm) boreholes to control gas accumulation in the upper corner of a fully mechanized working face in high-gas coal seams. The gas control process in the upper corner and gas interception in goaf by large-diameter boreholes was analyzed using the CFD model of the gas flow in goaf. The latter considered the control equation of gas flow, the established permeability model of goaf, and the gas emission law in goaf. Using the 2-105 working face of the Tenghui Coal Mine, Shanxi Province, China, as a case study, the distribution patterns of gas concentration and flow field in the goaf for various extraction flow parameters and different positions of boreholes were numerically simulated. The dependences between various locations, drainage flows, and the gas concentration in the upper corner were determined and fitted by engineering equations. The evolution pattern of the spontaneous combustion zone in the goaf under the drainage conditions was also analyzed. The optimal borehole configuration parameters ensuring the extraction flow rate exceeding 3 m·s −1 and the effective gas control in the upper corner of the working face at a distance of 5 m–15 m behind the working face were identified. The engineering practice proved the feasibility of gas control in the goaf using the adjacent roadway large-diameter borehole. The gas concentrations in the return airflow and the upper corner of the working face were kept below 0.65 and 0.8%, respectively, to ensure production safety and improve the gas utilization efficiency.

Numerous mountain highway tunnels in China do not satisfy the current traffic design standards and therefore need to be rebuilt or expanded. The drilling-blasting method is the primary method employed in China for expanding mountain highway tunnels, and it is crucial to monitor the vibrations caused by blasting. This study conducted a field investigation of the vibrations caused by blasting during the expansion of Yujiaya tunnel, which was built in 1999. The blasting-induced vibrations in the new and old concrete linings were monitored and analyzed during the expansion. The measured values of the peak particle velocity (PPV) varied within the range of 0.097–8.246 cm/s. The attenuation law of the PPV was determined via a regression analysis using Sadovsky’s empirical formula. The relationship between the main vibration frequency and the distance from the blasting source was expressed as a power function. Finally, the safety distances of the concrete linings subject to blasting vibrations were analyzed and discussed.

The coupled physical mechanism of heat conduction, moisture migration, and heavy metal transfer in a kaolin soil was studied by one-dimensional column tests. Two cyclic temperature tests show that, during the second cycle, the temperature close to the heat source of the soil column is lower than that during the first cycle and the temperature far away from the heat source is low, which reflects the influence of heating path. Correspondingly, the moisture content distribution during the second cycle is quite different from that during the first cycle. The higher the soil dry density is, the better the heat conduction is. The lower the dry density is, the more favorable the moisture migration is. The placement direction of the soil column and the set of temperature boundaries affect the moisture distribution of the soil column through the difference in the temperature, gravity, and solid matrix potentials. The temperature-driven liquid water movement effectively promotes the transfer of heavy metal contaminant in unsaturated soils; it is closely correlated with the convection of the heavy metal substances easily dissolved in liquid water. However, the transfer of heavy metal substances in unsaturated soil is not obvious without a thermal driving force. The test results for the different heavy metal ions indicate that the thermally induced transfer distance of the heavy metal pollutants with low adsorption properties (e.g., Cu 2+ ) to soil particles is much larger than that of the heavy metal pollutants with high adsorption properties (e.g., Cd 2+ ).