ABSTRACT
Large earthquakes induce a number of cycles of vibration of varying amplitude. Particularly under inelastic seismic response, such vibrations cause progressive damage and deterioration of resistance. Moreover, even a moderate level earthquake may also strain the reinforcing steel beyond its elastic limit thereby causing yield and permanent damage. As mild steel reinforcing bars generally possess a large reserve (monotonic) strain capacity, one-time yielding is generally not considered a serious issue. However, if the structure has sustained several post-yield cycles of loading, even though the concrete may be repairable, there remains substantial seismic induced fatigue damage to the reinforcing steel. Although restoration is required, seismic-induced fatigue damage to reinforcing steel is generally irreparable; the phenomenon is known as ‘low cycle fatigue’, representing a low number of large strain amplitude cycles.
