Limit Load Analysis for Fracture Prediction in High-performance Steel Bridge Members

Linear-elastic fracture mechanics has traditionally been used to assess the fracture initiation resistance of bridge structures in the presence of a fatigue crack. Because conventional bridge steels typically fail by brittle cleavage, this approach has worked reasonably well. The new generation of high performance steels (HPS) has significantly higher toughness compared to conventional steel. The failure mode changes to ductile rupture preceded by significant crack tip plasticity. Localized stress redistribution occurs prior to fracture, thereby minimizing the influence of local geometry on the fracture process. Under these conditions, limit load analysis provides an accurate method for fracture prediction in steel bridge members. The limit load analysis procedure greatly simplifies the computational procedures, making it a more practical tool for use by structural engineers. This paper demonstrates how limit load analysis can be applied to analyze the fracture resistance of Steel I-girders with fatigue cracks.