This project was undertaken to develop practical methods for determining drag and hydrostatic forces, on bridge piers and on superstructures, due to waterborne debris. The results are summarized in NCHRP Report 445, which includes recommended specifications for assessing these forces. The material in this report will interest bridge designers.

The accumulation of debris on bridge piers and on superstructures can create significant forces. Bridge designers must have reliable procedures to estimate the magnitude of these forces to ensure that the structure is properly sized. Under NCHRP Project 12-39, the University of Louisville developed equations for predicting the maximum debris forces. The equations were validated through small-scale laboratory tests at the University of Louisville, the University of Queensland (Australia), and the U.S. Army Corps of Engineers Riprap Test Facility. In addition, information collected at bridges that had been damaged by debris forces was included in the research.

The objective of this research was to develop practical design specifications and supporting commentary for the determination of impact, drag, and hydrostatic forces on bridge piers and on superstructures due to debris. The research effort included experimental studies conducted to determine a method for predicting debris forces on piers and on superstructures. A recommended specification and commentary on debris forces was developed, and three design examples were provided.