RISK ASSESSMENT OF CORBELS IN BUTTRESS DAMS

摘要

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