Nonlinear structural response characteristics of nuclear power plant shear wall structures

Nuclear power plant structures and equipment are designed to criteria that allow seismic stresses which are high enough to potentially cause nonlinear effects at the Safe Shutdown Earthquake (SSE) and above. In addition to the nonlinear effects of the soil and any uplift effects which may occur, yielding or cracking of the structural members will result in nonlinear response. For relatively low-rise structures such as are typically used for many nuclear power plant buildings, soil-structure interaction effects are often not as critical as for reactor containment buildings. For reinforced concrete shear wall structures such as auxiliary buildings, the principal structural nonlinear response effects are expected to occur as a result of yielding and degradation within the shear wall system. In order to determine the inelastic response characteristics of a typical nuclear shear wall structure at seismic response levels approaching failure, an investigation of a reinforced concrete auxiliary building using a nonlinear structure model was conducted. Stiffness degrading elements representing the shear walls were developed and responses at several levels of ductility up to that at which failure was considered imminent were evaluated. In order to obtain as accurate an evaluation of the structure capacity as possible, strength capacities for the structural elements were based on median centered properties rather than material design allowable values, as well as damping values considered appropriate for structures with significant inelastic response. Seismic input to the model consisted of a series of natural earthquake records scaled to peak ground acceleration levels which produced story ductility ratios up to approximately four. (orig./RW)