Zhi-Gang Xiao

CFRP REPAIRED WELDED THIN-WALLED CROSS-BEAM CONNECTIONS SUBJECT TO IN-PLANE FATIGUE LOADING

Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fiber-reinforced polymer (CFRP) sheets. Constant amplitude fatigue experiments are conducted on the repaired specimens. A pilot test is conducted on a T-connection of square hollow sections (SHS) to explore the effective method of applying CFRP. Due to the peeling effect at the corner region of the SHS-to-SHS connection, early debonding happens in the pilot test that only results in a slight extension in fatigue life. In the following experiments of repairing RHS-to-RHS cross-beam connections, circumferential or transverse restraining CFRP patches are applied in the corner region that prevents early debonding successfully and leads to significant increase in fatigue life. Finally, an improvement is made with the addition of steel strengthening plates that increase both the flexural stiffness and fatigue life of the cracked specimens significantly. The proposed retrofitting method may be useful for repairing other similar fatigue-cracked welded tubular connections.

Boundary element analysis of fatigue crack growth for CFRP-strengthened steel plates with longitudinal weld attachments

AbstractIn this paper, steel plates with longitudinal weld attachments strengthened by carbon fiber reinforced polymer (CFRP) laminates on one side were analyzed based on the boundary element method and compared with test data from the literature. Good agreement with the data indicated that the numerical analysis was reliable for estimation of the fatigue crack propagation of CFRP-bonded steel plates with longitudinal weld attachments. The effects of double-sided strengthening, double-sided weld attachment and CFRP stiffness on the fatigue behavior of retrofitted welded joints were also investigated. The results showed that double-sided strengthening was much more efficient than single-sided application. It was observed that the crack propagation of steel plates with weld attachments on both sides was accelerated compared with those with attachments on only one side. In comparison with steel plates without a weld attachment, the retrofitting efficiency, in terms of the fatigue life extension ratio, was si...

Evaluation of Stress Intensity Factor for CFRP Bonded Steel Plates

Recent studies on the application of carbon fibre reinforced polymer (CFRP) materials to defected steel structures have demonstrated the potential for significant reduction of stress intensity factor (SIF) values at crack tips leading to extended fatigue lives. However, most of the previous research relied on experimental and numerical methods, which were either expensive or time-consuming. In this paper, the SIF values at crack tips of steel plates strengthened with bonded composite materials were evaluated using linear elastic fracture mechanics. The analysis was based on the classical solution of SIF values of plain steel plates, considering load share effect and geometry correction factor change resulted from the overlay patch. The effect of different parameters were demonstrated and compared with experimental results, including initial damage degrees of specimens, geometric and mechanical properties of retrofitting materials and bond locations. Good agreement with the experimental data indicated that this approach could conservatively predict the SIF values with reasonable accuracy. A parametric study on variables including the CFRP modulus, the bond width and bond length was conducted based on this method to further investigate their effect on the SIF values.