part a- experimental: experimental analysis of crack propagation in pre-stressed concrete sleepers by fracture mechanics

this study investigates propagation of mode i crack in b70 pre-stressed concrete sleepers by fracture mechanics approach. a new experimental analysis is done for notched b70 pre-stressed concrete sleepers with replica test and image analysis. a scanning electron microscope test (sem) and an image analysis are applied for the replica test in order to determine crack length and crack mouth opening displacement (cmod). the experimental data extracted from the three-point bending load test of b70 sleepers are analyzed with fracture mechanics method. in this study, the fracture mechanics parameters of a sleeper are investigated based on nonlinear fracture mechanics (nlfm) principles for concrete material. sleepers with initial crack width of 8 mm and different initial crack lengths of 5 mm to 45 mm, with a 10 mm increasing step, are tested. five specimens’ of each group are loaded under three-point bending load test, in order to determine the propagated crack length, crack mouth opening displacement (cmod), final load and the specimens’ energy. the results showed that by increasing the crack-to-depth ratio, both final load and specimens’ energy values are decreased linearly. also, these analyses confirm that the structural behavior of the pre-stressed concrete sleepers can be predicted by a simple fracture mechanics test, such as beams in bending, provided that the related structural conditions like initial crack length and cmod, are known.