The National Academies

NCHRP 24-34 [Final]

Risk-Based Approach for Bridge Scour Prediction

  Project Data
Funds: $500,000
Research Agency: Ayres Associates
Principal Investigator: Peter Lagasse
Effective Date: 4/21/2010
Completion Date: 6/28/2013

The Agency’s Final Report  documents the results of an investigation of risk-based approaches for bridge scour prediction. The uncertainties associated with bridge scour prediction, including hydrologic, hydraulic, and model/equation uncertainty were identified and evaluated. An essential element of the research was the development of software that links the most widely used 1-Dimensional hydraulic model (HEC-RAS) with Monte Carlo simulation techniques. A set of tables of probability values (scour factors) is presented that allow associating an estimate of scour depth with a conditional (single event) probability of exceedance when a bridge meets certain criteria for hydrologic uncertainty, bridge size, and pier size. The tables address pier scour, contraction scour, abutment scour, and total scour. For complex foundation systems and channel conditions, a step-by-step procedure is presented to provide scour factors for site-specific conditions. An integration technique that incorporates the uncertainties associated with the conditional probability of a limited number of return period flood events provides a reliability analysis framework for estimating the unconditional probability of exceeding a design scour depth over the service life of a bridge. A set of detailed illustrative examples demonstrate the full range of applicability of the methodologies. A stand-alone Reference Guide is available to aid the practitioner in the application of the probability-based methodologies presented in this report.

Products Availability: The Reference Guide for Applying Risk and Reliability Based Approaches for Bridge Scour Prediction is published as NCHRP Report 761.

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