Reliability-based pier scour engineering

Our infrastructure is aging. There are many bridges over water in this country, and these aging bridges are now showing signs of weakening due to scour around the pier foundations. In response, engineers are being required to design “safe” bridge piers such that the pier foundations will not be undermined by local scour. In this paper, the problem of relating the risk of bridge failure to the estimated maximum local scour depth is examined. Since safety factors are commonly used to incorporate uncertainties into design, the relationship between the risk of failure and safety factors is examined. A best-fit pier scour model, rather than a conservative model, is used to develop a probabilistic approach to pier scour engineering. An example is provided to demonstrate the probabilistic approach. The level of risk for a bridge pier design is provided by the development of safety factors that are a direct reflection of the desired or allowable level of risk.