Cracking behaviour of GFRP-reinforced concrete panels under uniaxial and biaxial tension

Sabrah, Tamer Berry A. (2009) Cracking behaviour of GFRP-reinforced concrete panels under uniaxial and biaxial tension. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Fibre reinforced polymer (FRP) reinforcing bars for concrete have become the subject of research as an alternative to steel reinforcement which is susceptible to corrosion. This thesis encompasses an experimental investigation and theoretical modelling of the cracking behaviour of concrete panels reinforced with glass fibre reinforced polymer (GFRP) bars under uniaxial and biaxial direct tensile loading conditions. -- In the experimental phase of this investigation, a special setup is designed to test reinforced concrete panels under uniaxial and biaxial tension. The setup accommodates concrete panels that are reinforced with GFRP and/or steel reinforcing bars. The setup is used to carry out an experimental test program on twelve reinforced concrete panels under uniaxial and biaxial tension. The test parameters are the concrete strength, concrete cover to bar diameter ratio, bar spacing, reinforcement ratio, and bar type (GFRP or steel). The crack patterns, crack widths, and spacings are investigated. The tensile stress-strain relationships, and thus the tension stiffening behaviour, are examined. The tension stiffening behaviour is the concrete contribution in resisting part of the tensile stresses applied. -- The experimental results reveal that the crack development under biaxial tension affects the magnitude of the stress in the GFRP-reinforced concrete panels resulting in a decrease in the cracking loads and stresses. GFRP-reinforced concrete panels under uniaxial tension experience an increase in the tension stiffening contribution compared to steel-reinforced concrete at the same level of stress. However, this contribution is not significant under biaxial tension. GFRP-reinforced concrete panels under biaxial tension experience much less tension stiffening contribution than those under uniaxial tension due to different cracking mechanisms for both cases. In general, there is an increase in the tension stiffening contribution of GFRP-RC panels due to the decrease in the reinforcement ratio. The area of the effective tension zone of GFRP-reinforced concrete is found to be almost half the size of those that develop around steel reinforcing bars. The use of an effective tension zone for GFRP-reinforced concrete equal to seven times the bar diameter is recommended rather than using 15 times the bar diameter which is commonly used for steel reinforcing bars. The use of high strength concrete causes a reduction in the total number of visible cracks, and thus enhancing the structural behaviour of GFRP-reinforced concrete panels. -- An analytical cracking model is developed to predict the crack spacing and width of GFRP-reinforced concrete. The model accounts for the bond stress transfer mechanism and surface characteristics of the reinforcing bar. The model is validated through comparisons with test results and other existing experimental data The proposed model is very suitable to predict the cracking variables of GFRP-reinforced concrete. Furthermore, a tension stiffening constitutive model is proposed for non-linear finite element analysis of GFRP-reinforced concrete. The proposed model accounts for the biaxial tension strength envelope. The model assumes a bi-linear relation in the post-cracking range to reflect the tensile behaviour of the tested GFRP-reinforced concrete panels. This model is incorporated into an incremental elastic plastic concrete model that is used to perform a non-linear finite element analysis of GFRP-reinforced concrete panels. The analysis results show reasonable accuracy in predicting the behaviour of GFRP-reinforced concrete.

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