The principal causes of failure of bridges over rivers and streams are scour at the foundations, channel movement and hydraulic forces. scour is the removal of material from around piers and abutmentsdue to extreme flows, ice jams or debris which destroy the foundation support and result in excessive settlement or movement and loss of support for the superstructure. channel movement is the natural realignment of the river channel so that the stream encroaches on a pier, abutment or bent, resulting in failure from scour as described above. in addition, channel movement can erode the approaches to the bridge. hydraulic forces from the impact of ice or debris against a pier, abutment or superstructure can cause dislocation of the bridgeelements. buoyancy and flotation, as the result of submergence, canalso dislodge bridge decks off of their supports. a procedure for conducting a comprehensive hydraulic evaluation of existing bridges to determine their vulnerability to scour, stream instability, and hydraulic forces is given in this paper. the procedure is based on thefive step process recommended in the september 1988 fhwa technical advisory on scour. this paper appears in transportation research record no. 1290, third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 1.
Abstract