RISK ASSESSMENT OF CORBELS IN BUTTRESS DAMS

摘要

Most of the buttress dams currently in service today were designed and constructed between fifty and one hundred years ago. Not surprisingly, these older designs often do not meet present day requirements for the design of reinforced concrete sections. This is often the case with the corbels that support the slabs or arches in buttress dams. The corbels for buttress dams were typically not constructed with sufficient reinforcing steel to meet the ductility requirements of modern reinforced concrete codes. Under-reinforced corbels can fail in a sudden (brittle), unpredictable manner. If a corbel were to fail, it could result in loss of support for the upstream slab or arch, which would result in a breach of the dam. Therefore, a failure mode involving a corbel can have a significant impact on the overall safety of the dam. As a result, costly and potentially disruptive rehabilitation may be needed to provide the necessary degree of safety. The state of the practice in dam engineering is moving towards a risk-based approach to evaluating structures. This technique compares the risk of failure against the consequences of failure. Where a relatively low tolerance for risk exists, the contribution of risk from the corbels may be unacceptable, and changes in dam operation or rehabilitation of the corbels may be considered urgent. Similarly, where a greater degree of risk is tolerable, it may be acceptable to delay rehabilitation of the corbels. This paper discusses how risk analysis may be used evaluate the urgency of rehabilitating the corbels in buttress-type dams.