The effect of freeze‐thaw cycles on the axial tension and axial compression properties of completely carbonized concrete are investigated in this study. Three grade concrete specimens (C30, C40, and C45) were fabricated. The freeze‐thaw cycle test was carried out on the completely carbonized specimens, followed by axial tension and axial compression tests. The results show that completed carbonization increases the axial tensile peak stress of C30, C40, and C45 concrete specimens by 8.7%, 9.7%, and, 12.1%, respectively. The peak axial tension strain increased by 1.9%, 7.2%, and 9.6%, respectively. The peak axial compressive stress increased by 10.5%, 19.1%, and 24.1%, respectively. The peak axial compressive strain decreased by 13.7%, 14.1%, and 14.3%, respectively. With the increase of freeze‐thaw cycles, the peak stress of tensile stress, peak strain, and compressive stress of concrete decrease continuously. The peak strain of compressive strain increases. The lower the strength grade of concrete, the faster the decline rate of stress and strain. According to the data changes of peak stress and peak strain at different times of freeze thaw after carbonization, the stress‐strain curve fitting formula for concrete under freeze‐thaw cycles after complete carbonization is put forward, which has a good coincidence with the experimental result.

In order to study the failure mode and debonding behavior of the interface between BFRP (basalt fiber reinforced polymer) sheet and structural steel under mixed-mode loading conditions, eighteen specimens with different initial angles were tested in this study. The specimens were designed with different initial angles to ensure that the interface performed under mixed-mode loading conditions. The relations between the bond strengths, failure modes, and initial angles were investigated. A new evaluation method to predict the interfacial bond strength under shear-peeling loading mode was proposed. The test results show that specimens with a smaller initial angle are more likely to exhibit a shear debonding failure at the interface between the steel plate and adhesive. In contrast, specimens with a larger initial angle are more likely to exhibit peeling of the interface. The ultimate tensile strength of the specimen is higher with a smaller initial angle. The results predicted by the proposed method are in good agreement with the experimental results.

In order to study the influence of the axial compression ratio and steel ratio on the shear‐carrying capacity of steel‐truss‐reinforced beam‐column joints, five shear failure interior joint specimens were designed. The effect of different coaxial pressure ratios (0.1, 0.2, and 0.3) and steel contents on the strain, ultimate bearing capacity, seismic performance, and failure pattern of cross‐inclined ventral and chord bars in the joint core area was investigated. The experimental results show that the load‐displacement hysteretic curves of all test specimens exhibit a bond‐slip phenomenon. With the increase of the axial compression ratio, the ultimate bearing capacity of the joint core increases by 3.4% and 5.9%, respectively. While the ductility decreases by 10.3% and 13.1%, and the energy consumption capacity decreases by 3.2% and 5.8%, respectively. The shear capacity and ductility of the member with cross diagonal ventral steel angle in the joint core are increased by 12.9% and 13.4%, respectively. The shear capacity and ductility of the joint can be significantly improved by increasing the amount of steel in the core area. The expression of shear capacity suitable for this type of joint is obtained by fitting analysis, which can be used as a reference for engineering design.

Existing steel–timber structures may exhibit limited composite action between the two materials. To address this issue, this study proposes a novel sleeve-connected prefabricated steel–timber (SCPST) beam–column joint that utilizes steel sleeves and high-strength bolts for assembly. To assess its seismic performance, five full-scale interior joint specimens with different beam-sleeve thicknesses and lengths were tested under low-cycle reversed loading. The experimental results revealed that deformation and damage were concentrated at the beam ends, whereas the timber columns remained essentially elastic, satisfying the strong-column–weak-beam seismic design objectives. Within the tested specimen matrix, the peak load of the specimen with an 8 mm beam-sleeve thickness was 43.75% higher than that of the 4 mm specimen, while that of the specimen with a 400 mm sleeve length was 17.46% higher than that of the 300 mm specimen. Frictional slip at the timber–steel interfaces and yielding of the stiffeners were identified as the primary energy-dissipation mechanisms. Simplified analytical expressions based on Eurocode 3 and Chinese timber design provisions were developed to evaluate three potential beam-end failure modes, and the calculated resistances differed from the experimental results by less than 10%. A simplified finite element model was also established in ABAQUS. The simulated failure patterns and peak loads were in reasonable agreement with the experimental observations, with average peak-load errors of 2–6%. These results indicate that the analytical resistance estimates and simplified numerical model can provide a preliminary basis for evaluating the resistance and global response of SCPST joints within the investigated parameter range.

This study investigates two novel prefabricated frame joints: prestressed steel sleeve-connected prefabricated reinforced concrete joints (PSFRC) and non-prestressed steel sleeve-connected prefabricated reinforced concrete joints (SSFRC). A total of three PSFRC specimens, four SSFRC specimens, and one cast-in-place joint were designed and fabricated. Seismic performance tests were conducted using different end-plate thicknesses, grout strengths, stiffener configurations, and prestressing tendon configurations. The experimental results showed that all specimens experienced beam end failures, and three failure modes occurred: (1) failure of the end plate of the beam sleeve, (2) failure of the variable cross-section of the prefabricated beam, and (3) failure of prefabricated beams at the connection with the steel sleeves. The load-bearing capacity and initial stiffness of the structure are increased by 35.41% and 32.64%, respectively, by increasing the thickness of the end plate. Specimens utilizing C80 grout exhibited a 39.05% higher load capacity than those with lower-grade materials. Adding stiffening ribs improved the initial stiffness substantially. Specimen XF2 had 219.08% higher initial stiffness than XF1, confirming the efficacy of stiffeners in enhancing joint rigidity. The configuration of the prestressed tendons significantly influenced the load-bearing capacity. Specimen YL2 with symmetrical double tendon bundles demonstrated a 27.27% higher ultimate load capacity than specimen YL1 with single centrally placed tendon bundles. An analytical model to calculate the moment–rotation relationship was established following the evaluation criteria specified in Eurocode 3. The results demonstrated a good agreement, providing empirical references for practical engineering applications.