Influence of aging on the dynamic behavior of reinforced concrete shear wall structures

The natural frequency of reinforced concrete buildings for nuclear power plants gradually decreases over time after their completion, mainly because of the shrinkage of the concrete during drying and minor damage caused by seismic forces. In this study, a numerical analysis method that comprehensively considers both drying shrinkage and seismic forces and investigates their effects is proposed. The results of finite element (FE) simulations performed with the proposed method show that when only the drying shrinkage of concrete is considered, the natural frequency decreases by 30 % and the damping constant increases by 300 % when the final shrinkage strain rate reaches 95 %. Furthermore, the natural frequency decreases by 50 % and the damping constant increases by 600 % when short-term seismic forces are applied, causing story drift angles of approximately 2 × 10^–3. It was confirmed that these changes accelerate with repeated application of drying shrinkage and seismic forces. By comparing simplified simulations that consider the aging of stiffness and damping due to cumulative drying periods with FE simulations, seismic responses can be equivalently evaluated up to story drift angles of approximately 2 × 10^–3, while responses beyond this are overestimated compared to FE simulation, allowing for conservative evaluations. This work has practical usefulness in that it enables bridging between complex modeling and simplified methods based on current design codes. The findings contribute to the establishment of seismic safety evaluation methods that adequately account for the effects of aging on reinforced concrete structures used over long periods of time.