Economic Considerations in Designing Bridge Scour Countermeasures

The authors originally developed a model, HYRISK., to prioritize efforts on scour evaluations for bridges with unknown foundations. The model is based on data stored in the National Bridge inventory and accounts for ADT, detour lengths, value of lost time, bridge condition, bridge geometry, bridge age, and many other factors. An update to the model is presented which uses the HYRISK determined scour failure probability (or user defined failure probability) to evaluate the economic benefits of various countermeasure options. The model will provide information on the expected life of the bridge and costs and benefits of various levels of protection. The model determines the optimum level of protection for the bridge and the maximum expenditure that should be accepted to increase the level of protection. A computer tool has been developed which implements the methodology.