Advancing the State of Practice in Steel Bridge Evaluation: Application of the Master Curve and Fitness-for-Service for Existing Structures

Document Type

Conference Proceeding


Extending the service life of the existing steel bridge inventory is of great importance to owners, engineers, and end users. One concern for much of the aging infrastructure is brittle fracture. Many of these steel bridges were built prior to the implementation of the modern fracture provisions. Unfortunately, the understanding of fracture behavior and its application to steel structures is quite limited among the majority of practitioners. This is of particular importance in an industry where, due to the scale and scope of projects, construction, fabrication, and in-service defects are inevitable. The field of fracture mechanics has seen many advances over the past four decades, allowing for a greater understanding of brittle and ductile fracture. This improved understanding includes both the fracture behavior of structural steel and the application of material properties to structural evaluation. Specifically, the advancement of the master curve concept offers great value. The master curve concept allows for the characterization of fracture behavior in the brittle and brittle-ductile transition region, the behavior regime of most structural steels at service temperatures. Included in the master curve characterization are the size effects associated with cleavage fracture, as well as the distribution of fracture initiation sites throughout a material. It is this recognition of distributed initiation sites which allows for the statistical treatment of cleavage fracture behavior. Additionally, advancements beyond the concepts of the master curve have also been realized. Many industries around the world have developed standardized procedures for the application of fracture mechanics concepts to structural evaluation. Accounting for existing flaws in in-service structures, these fitness-for-service procedures provide information about the ability of a structure to function as initially intended. This paper provides an overview of the master curve and fitness-for-service principles. An example demonstrating their application for steel bridges as well as a discussion of the advantages gained through their implementation is presented. Embracing these concepts has the potential to promote safety while extending the service life of the aging inventory of steel bridges.