Thermal cracking of concrete slabs reinforced with fibre reinforced polymer bars
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AbstractUse of fibre reinforced polymer (FRP) reinforcement in concrete structures has increased remarkably in recent years. Fibre reinforced polymer reinforcements are made of high strength continuous glass, carbon, or aramid fibres impregnated with resin and have some excellent properties such as high resistance to corrosion, high strength-to-weight ratio, and good fatigue properties. Because of these excellent properties, FRP bars or grids have been used as reinforcement in many concrete bridge decks in North America. Bridge decks can be subjected to significant thermal gradients because of their exposure to variable environmental conditions. The thermal characteristics of FRP bars can be substantially different from those of concrete and conventional steel bars. The difference in thermal properties between FRP and concrete can have a significant influence on the behavior ofFRP reinforced concrete members when subjected to temperature variations. This research presents the results of an experimental investigation into the behaviour of FRP reinforced concrete slab panels under the effects of thermal gradients. Five concrete specimens (3m x 3m x 0.15m) reinforced with different types of FRP bars or grids were tested to investigate the effects of thermal characteristics of FRP on the development of thermal stresses and cracking and to examine the effectiveness of this type of reinforcement in controlling cracking due to temperature. The reinforcement ratio in each specimen was approximately equal to 0.6 percent. Temperature gradients were produced by heating the top surface of the specimens using infrared lamps while the bottom surface was exposed to room temperature. The specimens were simply supported at the corners while the displacement at the centre of the slab was restrained to zero to produce statically indeterminate moments causing tensile stresses at the bottom surface of the slab. The bending moment and the cracking developed by the thermal gradients were monitored and the strains in the reinforcement and the widths and spacing of the cracks were recorded. Following the thermal loading test, the specimens were subjected to a downward mechanical point load applied at the centre and increased monotonically up to failure. The results were compared to those obtained from testing a control specimen of the same dimensions but reinforced with conventional steel bars of the same reinforcement ratio 0.6 percent. The experimental investigation showed that the specimen reinforced with carbon FRP bars exhibited the best performance under thermal or mechanical loading in comparison with the specimens reinforced with steel or glass FRP bars. Smaller crack widths, strains in the reinforcement, and deflections were obtained in the carbon FRP reinforced specimen. The experimental results were also used to verify a finite element modelling of the test specimens using the computer program ADINA. Reasonably accurate predictions of the specimens' behaviour were obtained, particularly under the effects of thermal loading. However, under mechanical loads, the finite element analysis needs some improvement.
Bibliography: p. 135-137
CitationOsman, M. (2003). Thermal cracking of concrete slabs reinforced with fibre reinforced polymer bars (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/15992
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