Using fracture mechanics principles in steel bridge renovation projects

Steel bridges built in the post war period were not built for the current traffic intensities and are therefore prone to fatigue damage. The combination of high traffic intensities, low quality steel and suboptimal weld detailing can generate fatigue problems in existing bridges that could compromise the structural integrity of the bridge. Fracture mechanics principles can be used in steel bridge renovation projects, when S-N based calculation procedures do not predict sufficient structural capacity, as an alternative to potentially unnecessary strengthening of the considered detail. These principles have been used in the renovation of a 231 m long, plate-girder bridge in The Netherlands. Inspection intervals were derived for a non-load carrying, double fillet welded connection between transverse stiffeners and an I-shaped main girder. Such an analysis requires a detailed insight of the material's condition and therefore should be completed in close cooperation with the inspection operator to verify calculation assumptions. Using fracture mechanics allows the bridge owner to choose between inspecting a detail at a certain frequency or completing preventative strengthening. (paper)