Seismic Response and Frequency Degradation of Low-Rise RC Shear Walls: A Validated Nonlinear Model for Nuclear Structures

Abstract

Reinforced concrete (RC) shear walls are key seismic-resisting components in nuclear facilities, where reliable prediction of stiffness and damage under strong ground motion is critical. The evolution of natural frequency with damage is central to performance assessment and structural health monitoring. This paper validates a mesh-regularized nonlinear finite element model of low-rise RC shear walls with explicit focus on seismic response and frequency degradation relevant to nuclear structures. Four walls from the SAFE/CASH international benchmark program (T6, T7, T8, T9), sharing identical geometry but different axial load levels (0.2 MPa and 1.8 MPa) and horizontal reinforcement ratios (0.5% and 1.0%), are analyzed under three loading protocols: monotonic pushover, quasi-static cyclic, and pseudo-dynamic tests conducted at the ELSA laboratory. Concrete is represented by a smeared-crack model with fracture-energy regularization following the Hillerborg approach, and reinforcement by an embedded steel model with a cyclic Menegotto-Pinto constitutive law. The model accurately reproduces base-shear-drift envelopes and the dominant trend of frequency drop for all four walls, predicting peak strength within 2% error and frequency degradation within 10-15% of experimental values. However, it consistently underestimates cumulative hysteretic energy dissipation by up to 30% in high-axial-load cases (T7 and T9), indicating a conservative bias in energy absorption prediction. These results quantify both the reliability and limitations of a 2D smeared-crack approach for nuclear-type shear walls and provide practical recommendations on optimal mesh size, calibration strategy based on material test data, and the interpretation of frequency-based damage indicators for structural health monitoring in nuclear engineering applications.