Simplified Transformative Approaches for Evaluating the Criticality of Fracture in Steel Members

Connor, R.J. (2019). "Simplified Transformative Approaches for Evaluating the Criticality of Fracture in Steel Members," Engineering Journal, American Institute of Steel Construction, Vol. 56, pp. 201-209.

There has been considerable research and interest in the topic of fracture-critical members (FCM) during the past decade. As a result, the entire concept of what constitutes an FCM is being revisited, and many long-standing ideas and opinions related to this classification of members are being shown to be overly conservative. Significant advances in the understanding of fracture mechanics, material and structural behavior, fatigue crack initiation, fatigue crack growth, fabrication technology, and inspection technology have allowed other industries to address fracture--or, more importantly, control of fracture--in a more integrated manner. After years of research, new stand-alone AASHTO guide specifications that give codified direction on how to perform 3D system analysis to verify system redundancy, as well as guide specifications to evaluate internal member-level redundancy of mechanically fastened built-up members for both new and old bridges, have been proposed. Additional research demonstrating the benefits of exploiting the improved toughness of modern high-performance steel (HPS) grades has been completed. Through these advances, it is now possible to create an integrated fracture control plan (FCP) combining the original intent of the 1978 FCP with modern materials, design, fabrication, and inspection methodologies. Further, an integrated FCP provides economic benefits and improved safety to owners by allowing for a better allocation of resources by setting inspection intervals and scope based on sound engineering rather than based simply on the calendar. In summary, an integrated FCP encompassing material, design, fabrication, and inspection can ensure fracture is no more likely than any other limit state, ultimately allowing for a better allocation of owner resources and increased steel bridge safety. This paper summarizes some of the recent advancements related to the topic of the FCM and provides a suggested approach to providing more rational treatment of such members without compromising reliability.