Fatigue and post-fatigue monotonic behaviour of partially prestressed concrete beams

The objective of this work was to study the fatigue and post-fatigue monotonic behaviour of partially prestressed concrete (PPC) beams with a high degree of prestress. Eleven large PPC beams were tested under fatigue and monotonic loading. The effects of applied load level and severity of fatigue damage on the beams' fatigue and post-fatigue monotonic behaviour were studied and analysed. The results indicated that the fatigue behaviour of beams with a high degree of prestress was dependent on the applied load level. For an optimum and safe design, the applied load level should be less than 1·28 times the cracking load, the maximum crack width should be limited to 0·20 mm and the initial maximum stress range of non-prestressed reinforcing bars before repeated loading should be less than 170 MPa. The post-fatigue monotonic behaviour of beams was related to the severity of fatigue damage prior to the monotonic test. Low fatigue damage was found to have only a slight impact on the monotonic behaviour of the beams, whereas medium and high fatigue damage respectively reduced the ultimate strength by up to 15·2% and 18·0% and increased the deformability ductility index by up to 18·6% and 41·0%.