Evaluation of Steel Bridge Details for Susceptibility to Constraint-induced Fracture

Abstract

Historically, reports of significant problems associated with details featuring intersecting welds in steel bridges have been rare. However, there have been several notable cases involving constraint-induced fracture (CIF). CIF is a particular concern since it can occur in a brittle fashion, suddenly and without warning (different from other types of problems, such as corrosion or fatigue crack growth, for example). CIF generally occurs in details that feature a high degree of constraint (leading to a high level of stress triaxiality), in combination with high levels of tensile stress (particularly from residual stresses) and the presence of a notch-like or crack-like planar discontinuity approximately perpendicular to the primary flow of tensile stress. Details subject to a high degree of constraint often feature the intersection of two or three welded structural elements. The distinction between “intersecting welds” and “constraint resulting from the intersection of welded structural elements” is important. This paper summarizes the findings and recommendations of a recently completed report reflecting the current state of knowledge about CIF in steel bridges. The report is based on a review of previous research, industry practices, and the input of a panel of steel bridge industry experts. It provides a review of the fundamental principles of CIF and presents a general procedure for evaluating steel bridge details for susceptibility to CIF, including examples of assessments of commonly used steel bridge details.