FEDERAL HIGHWAY ADMINISTRATION BRIDGE SCOUR PRACTICE

The national attention given to scour-associated highway bridge failures since 1987 coupled with the paucity of press coverage on this issue prior to that time suggests that scour failures are of recent vintage. This is, in fact, not so. For example, 17 highway bridges failed due to scour in the northeastern part of the nation in the same relative time frame that the Schoharie Creek/New York Throughway bridge lost its battle to scour in April 1987. The Federal Highway Administration and State highway agencies have been conducting research on bridge scour and considering scour in the design process for many years. Periodic highway bridge failures due to scour from the 1950's onward have provided the impetus for continued investigation of the mechanics of such failures with some advances in the design process. It was not, however, until the 1987 Schoharie Creek bridge failure that sufficient national interest focused on the issue to generate the need for national direction within the Federal-aid highway program. In September 1988 the Federal Highway Administration published Technical Advisory 5140.20, Scour at Bridges, to address bridge scour in the overall context of the design process and in the inspection of existing structures within the National Bridge Inspection Standards Program. This paper presents the elements of the bridge scour challenge, the state-of-the-art basis of scour evaluation and countermeasures to protect bridges against scour, all based on the Federal Highway Administration Technical Advisory 5140.20 and Hydraulic Engineering Circular No.18, both entitled Scour at Bridges. The national status of the program is also presented. All of these issues are presented from the perspective of the Federal Highway Administration's role in the bridge scour program.