Full-scale experimental research on the bending fatigue performance of post-tensioned prestressed concrete pipe piles

Post-tensioned prestressed concrete pipe piles (large cylinder piles) have been widely used in port and bridge engineering because they are economical and deliver excellent performance, and thus, have potential for use in offshore engineering. However, limited research has been devoted to the bending fatigue of large cylinder piles, which is essential for offshore engineering design. This study evaluated the bending fatigue of large cylinder piles by performing a series of full-scale bending fatigue tests on three specimens (L = 12 m, D = 1.2 m) and numerically analyzing the static cracking patterns in them. The static performance of large cylinder piles, including the bending moment of static cracking (Mcr) and its patterns, was analyzed by using a validated finite element model. Three-point bending fatigue tests with cyclic loading under a constant amplitude (stress ratio R = 0.4, peak fatigue load = 37.72%–80.00% Mcr) were then conducted to examine the development of mid-span displacement and stiffness degradation in the specimens. A critical damage factor (Dcr), which uses the cracking of concrete as the indicator of termination of the test, and a modified approach to prediction were then proposed and applied, based on findings of the fatigue test and past literature, to predict the number of cycles that it took for the large cylinder piles to crack. Finally, bi-linear S–N curves were plotted by considering the effective prestress according to the experimental and estimated data. The results here provide a theoretical basis for the fatigue-based design and application of large cylinder piles.