Fatigue tests and calibrated fracture mechanics approach for historical riveted steel girders

For historical riveted steel railway bridges fatigue assessment and calculation of the remaining fatigue life based on SN-curves is a big challenge, due to missing traffic data of the past and often unsatisfactory conservative results (no remaining fatigue life, but no fatigue cracks detected). As an alternative, a fracture mechanics approach based on the assumption of an initial crack length and an analysis of the stable crack growth behaviour seems helpful. Within a research project, four dismounted girders of the carriageway of an old steel lattice girder bridge (year of construction: 1908, end of service life: 2018) were used for specific fatigue tests in the laboratory. Starting from artificial notches, initial cracks at the critical positions at the rivet holes of riveted girders were induced and the development of the crack fronts was measured, simulating rivets with and without clamping force. First, the scope and execution of these fatigue tests are presented in the paper, completed by a comprehensive evaluation of the development of the crack fronts. Then a simple fracture mechanics model is presented and calibrated based on the test data. With this model the remaining fatigue life of riveted girders, with high fatigue pre-damage, can be determined for the borderline cases either without or with high clamping forces in the rivets.