Aging and design of concrete members reinforced with GFRP bars

Strength and stiffness properties of GFRP bars and moisture transport phenomenon into the bars was investigated in this research for various conditioning schemes with and without the application of sustained loads. Low viscosity urethane modified vinylester resin is identified as the most suitable resin, from the durability viewpoint.;Based on accelerated test results calibrated with respect to naturally aged results it is safely concluded that the service life of the FRP bars with durable resin is about 60 years as a minimum with 20% sustained stress on the bar. Concrete cover protection on the GFRP bars enhanced the service life up to an additional 60 years. Bond strengths between concrete and GFRP did not decrease under salt and tap water immersion of pull-out specimens subjected to freeze-thaw variations. Compression failure philosophy has been developed for moment resistance and serviceability limit states were established based on curvature limit of 0.005/d, which unifies other limit states such as crack-width and deflection. Average bond strain of 0.006 in./in. for GFRP stirrups provides good theoretical correlation with experimental results on shear capacity from this research as well as those of others.;From this research it is evident that despite reduction in the properties of GFRP bars over time in the concrete environment, moment capacities of the beams were not affected provided compression failure philosophy is used. Advantages of compression failure over tension failures was systematically investigated for GFRP reinforced concrete beams under both static and fatigue loads. Reduction in the moment capacity of GFRP reinforced concrete beam designed for tension failure and vulnerability against fatigue loads was clearly demonstrated. Maximum concrete strains at working loads should be preferably well below 750 x 10-6 (25% of epsiloncu) for GFRP reinforced concrete beams designed for compression failure due to fatigue considerations. In addition, conservative reduction factor of 0.75 is proposed for the time dependent factor xi, used by ACI Eqn. 9--10 for the purpose of approximately estimating long-term deflections resulting from creep and shrinkage. Many findings in this investigation lead to the approval of design guidelines for FRP reinforced concrete structures through ACI 440-H