The load and resistance factor design (LRFD) framework for foundations of bridges and other structures provides state departments of transportation (DOTs) the opportunity to adapt and improve local resistance factors—other than those generally prescribed in the code—based on geology, design practice, and construction methods through statistics and reliability analysis. The codified AASHTO LRFD resistance factors were developed based on load tests conducted across the country, with variable conditions and practices. This approach, while allowing broad applicability, results in comparatively large coefficients of variation and conservative resistance factors. While many DOTs use these codified resistance factors, others have invested in evaluation of local geology and local design practice, and have established and adopted resistance factors for these specific design or construction practices. DOTs have used different methods to locally calibrate various resistance factors associated with different design methodologies or foundation construction control.
The objective of this synthesis is to document the extent to which state DOTs have developed local resistance factor calibration, methods used for development, which factors have been calibrated, and how locally calibrated factors have been used.
Information to be gathered includes (but is not limited to):
• Which DOTs have developed local resistance factor calibration;
• State DOT programs or research initiatives used to calibrate the resistance factors (e.g., how is it funded and organized);
• Which resistance factors are calibrated;
• Methods used for calibration (e.g., statistical methods, calibration to past practices);
• How and when the calibrated factors are used (e.g., size of project, construction practices, soil types, category or class of structures);
• Methods used for the exchange of data associated with site investigation and characterization or foundation performance testing;
• Existence and uses of DOT databases and whether these databases are shared outside of the DOT (e.g., site information, borings, load testing);
• How DOTs validate and refine locally calibrated resistance factors (e.g., performance monitoring, load tests); and
• Challenges identified by DOTs for local resistance factor calibration.
Information will be gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected agencies for the development of case examples. Information gaps and suggestions for research to address those gaps will be identified.
Completed report can be found at NCHRP Synthesis Report 601.