Advances in new materials have brought about renewed discussion of the traditional definition of what constitutes a fracture-critical (FC) steel bridge. For example, modern steel bridges are often built of high-performance steel and fabricated using higher quality welding procedures with a composite deck slab and, therefore, are inherently more capable of carrying redistributed loads through alternate paths. Currently, the stringent fabrication and maintenance inspection requirements for FC bridges steer owners and designers away from building new FC bridges although allowed by the AASHTO code with the appropriate design, construction, and inspection procedures. The increased maintenance inspection costs are also a concern of existing FC bridges.   These additional costs, and any structural concerns, could be eliminated or minimized by re-examining the FC designation and reclassifying bridges where justified.  But, designers and owners often have deferring opinions on the definition of a FC bridge. The AASHTO code does not give guidance on the appropriate methods for fracture analysis. Although individual designers have developed methods for this issue, there is no consensus on the loadings, the approach, and what constitutes failure.

The objectives of this research are to (1) develop a methodology to quantify when a steel bridge system is considered FC based on loads, existing conditions, material properties, and bridge configurations, and (2) recommend AASHTO specifications using the methodology in the design of new bridges and the evaluation of existing bridges.

Deliverables in this phase shall include:

1. A critical review of existing specifications, technical literature, owners and industry experiences, NCHRP Report 406: Redundancy in Highway Bridge Superstructures, and ongoing NCHRP research, as well as the System Factors in the AASHTO Manual for Bridge Evaluation. The review should cover research findings from both foreign and domestic sources.
2. A proposed methodology to quantify when a steel bridge system is considered to be FC. The proposed methodology should consider at least the following: live load capacity before and after fracture, load combinations, fatigue, ADTT, bridge age and existing conditions (e.g., corrosion, damage, and cracks), material properties, and transverse and longitudinal bridge configurations.
3. A detailed outline for the recommended AASHTO specifications to determine if a bridge system is FC for the design of new bridges and evaluation of existing bridges.
4. Interim Report No. 1 that documents deliverables 1 through 3 of Phase I and provides an updated work plan for the remainder of the project no later than 4 months after contract award. The updated plan must describe the process and rationale for the work proposed for Phases II through IV.

Phase II—Methodology Development and Validation
Deliverables in this phase shall include:

1. A fully developed methodology to quantify when a steel bridge system is considered FC based on loads, existing conditions, material properties, and bridge configurations. The methodology should be validated using existing field and lab testing data.
2. A sample section of the recommended AASHTO specifications that is publication ready with appropriate level of detail.
3. Interim Report No. 2 that documents deliverables 1 through 2 of Phase II and provides an updated work plan for the remainder of the project no later than 12 months after approval of Phase I. The updated plan must describe the process and rationale for the work proposed for Phases III through IV.

The deliverable for this phase will be recommended draft AASHTO specifications and examples that cover different bridge types including as examples 2- and 3-girder simple and continuous bridges, and truss bridges. The examples should cover newly designed and existing bridges.

Deliverables in this phase shall include:

1. Revised specifications and examples after consideration of panel’s comments.
2. An implementation plan.
3. A final report that documents the entire research effort.

STATUS: A decision was made to discontinue work on the project beyond Phase I. The remaining work will be conducted under NCHRP Project 12-87A.