ABSTRACT
Extreme events include scour, earthquake and collision loads. In the past, each extreme event was considered separately, and combinations were considered as a conservative simultaneous occurrence of these events. There is a need for the development of rational design criteria for combination of scour, vessel collision and earthquake. Effect of earthquake is a function of ground (bedrock) acceleration, structural system specific parameters, and component-specific parameters. Scour is not considered as a load, however, it can have a considerable effect on bridge performance because of load re-distribution. It is the major cause of bridge failures in the United States. There are three types of scour: long-term channel degradation (or aggradation), contraction scour, and local scour. Occurrence and magnitude of scour can be affected by a flood event. Vessel collision can be represented by a time varying product of three variables representing variation in the vessel collision force, variation due to uncertainty in transition from load (vessel collision) to load effect in a component (moment, shear forces, axial force), and variation due to approximate method of structural analysis. The major parameters which directly affect the vessel impact force are: type (barge ship), displacement tonnage, and speed. However, the actual collision force is also dependent on site-specific parameters that include: waterway characteristics and geometry; vessel and/or barge configurations; and bridge type and geometry. Expected collision forces can vary widely.
