Risk-Based Design of Bridge Scour Countermeasures

HYRISK was originally developed to prioritize bridges with unknown foundations to determine where to spend limited resources to investigate those bridges. It was later modified to prioritize bridges of any type for scour evaluations where there are limited resources for the evaluations each year. The model is based on information that can be read from the National Bridge Inventory and accounts for average daily traffic, detour lengths, value of lost time, risks associated with scour at various types of foundations, bridge condition, bridge geometry, and bridge age. The model can readily be modified for use as a decision tool to select various levels of countermeasures for a bridge that has already been evaluate and determined to be scour critical for some probability flood event. For that application, the model can use the determined probability of failure and does not need to rely on the assumed risks for various foundation types. The model will need to account for the risk of loss of life on the basis of recent experience. The bridge owner will provide information on the expected life of the bridge and the costs of various levels of protection. The model will determine the optimum level of protection for the bridge and the maximum expenditures that should be accepted to increase the level of protection.