Modeling of IC Debonding of FRP-Strengthened Concrete Flexural Members
The presence of a fiber-reinforced polymer (FRP) strengthening material bonded to the tension face of a reinforced concrete beam will restrict but not prevent the opening of intermediate flexural cracks due to applied loading. Test results indicate that displacements at the toe of flexural cracks create stress concentrations at the interface of the FRP laminate and the beam, leading to the development of localized interface cracks that, typically, propagate, under the effect of the load, to join the original flexural cracks and cause delamination of the FRP system. This type of FRP delamination is commonly termed intermediate crack (IC) debonding. In this paper the analytical models published in the literature are reviewed and it was found that these models do not correlate well with measured experimental results. This paper proposes an analytical model that characterizes the interface shear stress based on two distinct sources: (1) the change in the applied moments along the length of the member and (2) ...
Effects of moisture on debonding in FRP-retrofitted concrete systems
FRP (fiber reinforced polymer) retrofit systems for reinforced concrete (RC) structures have been widely used in the past 10 years, and numerous studies on its short-term debonding behavior have been conducted extensively. Nevertheless, long-term performance and durability issues regarding such debonding behavior still remain largely uncertain and unanswered. In this study, comprehensive experimental and analytical investigations of debonding in FRP bonded concrete systems under long-term environmental exposure, namely moisture, have been performed to develop mechanics-based predictive debonding failure models and related design tools for the prevention of debonding failures. The experimental approach involves an investigation of debonding under moisture ingress, moisture reversal, cyclic moisture conditioning, using the concept of fracture mechanics and meso-scale tri-layer fracture specimens. Prolonged exposure to moisture condition has been shown to result in significant degradation of the FRP/concrete bond strength, while an irreversible weakening in the bond strength has also been observed in the fracture specimens under moisture cyclic condition. A predictive model has been developed based on the experimental results of the fracture specimens under variable cyclic moisture conditions for service life prediction of the FRP-strengthened systems. To incorporate this quantification method and experimental data, finite element analysis and correlation study have been conducted for RC beams externally strengthened with FRP plate. The cohesive zone model for interfacial fracture has been implemented, for which the properties of the interface were obtained from the meso-scale fracture tests. Test on laboratory-scale FRP-strengthened RC beam specimens under continuous moisture conditions has demonstrated the applicability of the methodology. In addition, molecular dynamics simulation has been conducted to gain more fundamental understanding of interface fracture behavior in bi-layer material systems (i.e. crack initiation and propagation direction) and the effects of material and interface properties at atomistic scale. Finally, a recommendation has been made to the current design of RC beams strengthened with FRP to prevent premature failure due to long-term exposure to moisture. Thesis Supervisor: Oral BytiUk6zttrk Title: Professor of Civil and Environmental Engineering
Substation automation based on IEC 61850 with new process-close technologies
New technologies in primary equipment like nonconventional instrument transformers require new interfaces to the substation automation system. The future standard IEC 61850 perfectly supports this requirement. With the introduction of the new technologies and the use of IEC 61850, a more decentralized architecture of the substation automation system will be possible. This provides several benefits but a careful system design is required to maintain the overall reliability of the system.