Fatigue crack initiation prediction of cope hole details in orthotropic steel deck using the theory of critical distances

Orthotropic steel decks are vulnerable to fatigue cracking in welded connections and complex geometrical details. A total of three fatigue tests were conducted on segments of orthotropic steel deck to evaluate the fatigue performance of trough-to-crossbeam connections with various cut-out configurations. In the tests, the specimens were subjected to cyclic three-point bending load and the fatigue cracks were more likely to initiate from the cope holes in the crossbeam web rather than the trough-to-crossbeam fillet welds. Three-dimensional finite element models (FEM) of the specimens were built and validated by the measured deflections and stresses. Using the validated FEM, the characteristic stresses based on the theory of critical distances (TCD) were calculated for the stress concentrations along the cope holes. The fatigue crack initiation life, predicted by the TCD-based stress combined with the plain material S-N curve, agreed reasonably with the fatigue test results. The TCD method could further form a basis of fatigue crack propagation analysis using the fracture mechanics approaches.