Viet Hai Do

This study aims to present a novel approach to assess the bond behavior of various types of FRP bars in concrete, based on an extensive dataset. The novelty of this research lies in evaluating both the bond strength and the critical slip, which forms the basis for creating a bond model between the bars and concrete. Furthermore, the model is constructed using advanced machine learning techniques, specifically gene‐expression programming (GEP), and its reliability is ensured by relying on a more extensive and diverse experimental dataset compared to previous studies. To train and validate the GEP model, data were collected from experiments involving 793 test specimens, categorized into five groups based on surface treatments: smooth (Sm), sand‐coated (SC), helically wrapped (HW), grooved (Gr), and a hybrid surface (Hbr) achieved by combining SC and HW. The model also considers a wide range of other parameters, including compressive strength of concrete and diameter, tensile strength, elastic modulus, and embedment length of FRP bars. The verification results using a separate testing dataset demonstrate that the proposed models accurately predict the bond strength and critical slip of FRP bars in concrete, achieving R² values of 0.794 and 0.88, respectively. Comprehensive parametric analyses are performed to clarify the influence of key parameters on the bond and slip behavior of FRP bars in concrete. The analysis results confirm the critical role of the surface type and elastic modulus in enhancing bond strength; particularly, among the different surface treatment methods, the HW treatment exhibits the highest bond strength, followed by the HBr, Gr, and SC surface types.

This study examines the aerodynamic performance and surface pressure distribution features of circular and helical fillet stay cables when subjected to wind using wind tunnel testing. The research seeks to clarify the aerodynamic performance disparities between conventional circular stay cables and helical fillet cables, providing valuable insights into their appropriateness for cable-supported structures exposed to wind-induced vibrations. The study initially investigates the aerodynamic efficiency of circular and helical fillet cables. Afterward, the wind tunnel captures the distribution of surface pressure on both cable surfaces. The findings suggest that circular stay cables may undergo cable dry galloping, whereas helical fillet cables demonstrate stability when subjected to wind forces. Furthermore, there are noticeable differences in the surface pressure distribution patterns between circular stay cables and helical fillet cables. Circular stay cables provide a symmetric distribution of pressure, with uniform pressure magnitudes along their surfaces, forming a symmetric pattern. On the other hand, helical fillet cables exhibit modified airflow patterns, leading to asymmetric pressure on the cable surface. Furthermore, the dry galloping observed in circular cables is attributed to the presence of low-frequency components. In contrast, helical fillet cables exhibit a more regulated incidence of low-frequency vortices, making them less prone to wind-induced vibrations.

One issue to consider while designing and constructing steel girders reinforced with carbon fiber-reinforced polymer (CFRP) plates in bridges is debonding failure. Previous studies showed that the parameters such as characteristics of material, load, adhesive, and CFRP plates have an effect on the failure probability of steel girder, which is represented by the reliability index. Therefore, this study analyzes the reliability indices of steel girders in bridges strengthened with CFRP plates to clarify the effects of debonding failure. Debonding and strength limit states are used to compare differences in reliability indices of different design scenarios. Strength and debonding margin the functions for the strength limit state and debonding limit state will be established in this study. The probability of failure is determined by a Monte Carlo simulation (MCS). It is found that the reliability index of debonding limit state is much lower than that of the strength limit state. This shows that the debonding failure should be considered significant in the reliability analysis of steel bridge girders strengthened with CFRP plate.