FATIGUE BEHAVIOUR OF A FIBRE-REINFORCED-PLASTIC GRID AS REINFORCEMENT FOR CONCRETE

Bridge decks are subjected to repeated loads from moving vehicles. Such repeated loads cause the stress in the reinforcement to vary cyclically millions of times during the service life of the bridge. It is therefore important to study the fatigue behaviour of FRP reinforcement for bridge decks. Tension-tension fatigue tests were carried out on bar specimens taken from two types of FRP grids, one made of carbon and glass fibres and the other of carbon fibres only. Tests were conducted under several stress ranges at room temperature to determine the relationship between stress range and fatigue life and the residual tensile strength of specimens that survive 40 million cycles of loading. Some tests were repeated at the lower and the upper extremes of temperature anticipated in the Canadian climate to determine the effect of temperature on the fatigue behaviour. The tests indicate that for a FRP grid made of carbon fibres only and cycled for 4 million cycles at a rate of 5 Hz to a maximum stress of 60% of the ultimate strength, more than 75% of the ultimate tensile strength is retained. For a grid predominantly made of glass fibres, more than 85% of the ultimate strength is retained if the maximum stress does not exceed 30% of ultimate.