For a realistic evaluation of the fatigue behaviour of FRP reinforcements, a specimen for direct-tension fatigue tests has been developed in which the FRP bar is completely encased in concrete. Extensive fatigue testing is in progress to determine the relationship between maximum stress and fatigue life for FRPs made of carbon, aramid and glass fibres. Test parameters include stress ratio, cycling rate, alkalinity and salinity of concrete, and temperature. Results obtained so far from tests conducted at a cycling rate of 4 Hz on a carbon-epoxy FRP bar under a constant stress ratio of 0.1 indicate that the maximum stress should not exceed about 38% of the bar's tensile strength for a desirable fatigue life of 4 million cycles.
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