Using Risk to Manage Bridges with Unknown Foundations

Research recently funded by the National Cooperative Highway Research Program (NCHRP) focused on developing risk-based guidelines to assist bridge owners in evaluating and prioritizing various courses of action for managing bridges with unknown foundations for scour failure. These guidelines will soon be finalized and made available to bridge owners nationwide. As of 2006, more than 57,000 bridges over water have unknown foundations. Managing these bridges for risk of failure is extremely difficult since a critical scour depth cannot be determined in the absence of foundation information. The guidelines developed under this research project focus on the following: 1) Simple estimation of risk of failure as a function of estimated failure probability and associated economic losses, 2) Establishing minimum performance standards for various bridge classifications, and 3) Justifying appropriate data collection activities (including nondestructive testing of foundations), scour monitoring activities, and scour countermeasures. These guidelines present a logical plan of action for bridges with unknown foundations. Given the large population of such bridges and the potential cost of management options, these guidelines will assist bridge owners in selecting and prioritizing management activities. The guidelines were recently tested by applying them to sixty bridges in six states with a variety of physical settings, structural conditions, and traffic loads: 30 bridges with known foundations and scour evaluations (i.e. for validation), and 30 bridges with unknown foundations (i.e. for demonstration). The results from these case studies, which were shared and discussed with state officials, show that the proposed methodology yields reasonable management plans.