Fragility Analysis of Concrete Gravity Dams

Concrete gravity dams are an important part of the nationʹs infrastructure. Many dams have been in service for decades. During the service life of a dam, operating conditions and natural environmental factors may have led to some deterioration in its structural integrity, mechanical equipment, and foundation. Moreover, advances in the methodologies by which design-basis events for natural phenomena hazards are identified have caused these events to be revised upward, in some cases significantly. An increasing number of existing dams fail to meet the more recent performance criteria. A fragility model of a dam provides a tool for rational safety assessment and decision making by using a probabilistic framework to manage the various sources of uncertainty that affect dam performance. In this paper, basic fragility concepts are presented, and databases required to support the fragility assessment are identified. The method is illustrated using a concrete monolith from the Bluestone Dam in West Virginia, designed in the late 1930s. Traditional design practices have been sufficiently conservative that the probability of dam failure under a probable maximum flood 11 m (36 ft) higher than the original designbasis flood remains small.