Experimental Analysis of Fracture and Damage Mechanics of Pre-Stressed Concrete Sleepers B70: Part B Analysis

Initial cracks occur in high strength concrete sleepers for various reasons, such as shrinkage and wrong curing and long lifetime of over 50 years of sleepers. These cracks may lead to complete failure of the structure. In order to more accurately design the sleepers, fracture mechanics (not strength of materials) should be incorporated. In order to achieve this purpose, it is important to forecast crack growth and residual strength reduction rate. In this study, based on the principles of nonlinear fracture mechanics (NLFM) in concrete material, fracture behavior of pre-stressed concrete sleepers was investigated. Sleepers with the lengths of initiation crack of 5 mm with 10 mm step increasing to 45 mm were tested. Five specimens in each group were loaded under three-point bending test, in order to calculate K_k , crack growth, and load-displacement diagram. The results showed that by increasing the crack-to-depth ratio, initial toughness, crack stability, and crack unstable toughness, the crack instability expansion begins. By increasing the crack-to-depth ratio, both initial and unstable toughness values increased linearly versus LEFM theory. Damage begins with an initial crack like in flexural damage and then continues with bifurcation of the crack. The influence of shear damage in sleepers crack growing leads it to the ultimate damage.