|Title:||Long-term behavior of bond between FRP and concrete exposed to a humid subtropical environment : experimental study and predictive modeling|
|Subject:||Fibrous composites -- Testing.|
Polymeric composites -- Testing.
Composite-reinforced concrete -- Testing.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Civil and Environmental Engineering|
|Pages:||xiv, 145 pages : illustrations ; 30 cm|
|Abstract:||Fiber reinforced polymer (FRP) composites have been widely applied in many fields such as the aerospace industry for many years. Compared with steel which is a commonly used modern construction material, the FRP composites have the advantages of excellent corrosion resistance and high strength-to-weight ratio. The corrosion resistance of FRP can benefit the long-term performance of reinforced structures, while the high strength-to-weight ratio leads to great ease in site handling, which reduces labor cost and interruptions to existing services. While a large number of studies have been conducted for the short-term performance of FRP-strengthened reinforced concrete (RC) structures, uncertainty is still remaining in their long-term performance. Indeed, lack of proper understanding of the durability of the FRP-strengthened RC structures has in return impeded a wider adoption of this technique in practice.In this present study, the long-term performance of FRP-to-concrete interfaces and FRP-strengthened RC beams subjected to accelerated wet-dry cycles, which simulate a sub-tropical environment, is investigated. The thesis consists of four parts of work: (1) Evaluation of the degradation of materials used in the FRP-strengthened RC structures to provide a reference for the following durability study on FRP-to-concrete interfaces and FRP-strengthened RC beams. The concrete, FRP composites and adhesive materials were tested after 8 months of accelerated dry-wet cycle exposure. (2) Examination of the long-term performance on FRP-to-concrete interfaces subjected to accelerated wet-dry cycle exposure, with the aim to establish a series of exposure-based interfacial bond-slip models;(3) Assessment of the durability of FRP-strengthened RC beams, which experienced 8 months of accelerated dry-wet cycle exposure. Finite Element (FE) analysis was conducted to simulate their mechanical performance with due consideration of the degradation of materials and FRP-to-concrete interfaces; (4) The long-term performance of FRP-strengthened RC beams under sustained load. Four beams were loaded under two different load levels for 9 months and the beam deflections were continuously measured using the fiber optic sensing technique. FE simulations were also conducted to reproduce the time-dependent beam deflections in comparison with the test results. Static loading tests were also conducted on the beams at the end of the sustained loading.|
The following findings have been obtained from the above studies: Degradations were observed in FRP-to-concrete interface after 8-month exposure, while their degree varied in different types of FRP systems. The proposed exposure-dependent bond-slip model gave a good prediction of the degraded bond behavior; (b) The load capacity of FRP-strengthened RC beams decreased by 1.4% to 10.8% after 8-month exposure in wet-dry cycles, while increase in stiffness of beams was also observed; (c) Carbon FRP (CFRP)-strengthened RC beams were subjected to 300 days sustained loading. The time dependent deflections were 1.76~2.60 times the instantaneous deflections. However, no significant change was observed on the load-carrying capacity of the strengthened beams after the sustained loading regardless of the sustained load levels. (d) The FE models developed in this study with the implementation of appropriate bond-slip models of the FRP-to-concrete interface, can effectively predict the long-term behavior of FRP-strengthened RC beams with due consideration of the effects of weathering and sustained loading.
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