Fragility and Economic Evaluations of High-Strength Reinforced Concrete Shear Walls in Nuclear Power Plants

Recent research studies have investigated the use of high-strength materials in nuclear power plant structures to enhance the constructability of their massive squat RC shear walls. For example, high-strength reinforcement bars can significantly reduce the required steel areas, thus minimizing material/fabrication costs, reducing rebar congestion, facilitating concrete consolidation/placement, and simplifying quality control checks. High-strength concrete can also limit cracks and deflections because of its enhanced mechanical properties, including the elastic modulus and compression/tension strength. Despite the advantages of high-strength materials, the dynamic response of their squat nuclear shear walls has not yet been fully investigated when different design parameters are adopted. To address this, the current study focuses on developing fragility functions for squat RC shear walls with high-strength materials to evaluate their seismic response compared with their counterparts with normal-strength materials; the economic benefits of both material walls were also assessed. In this respect, a numerical model was developed and then validated using previous experimental programs that have been conducted on RC shear walls with different aspect ratios, vertical/horizontal web reinforcement ratios, yield/ultimate strengths of reinforcement, concrete compressive strengths, and axial load levels. Following the model development and validation, incremental dynamic analyses using 44 far-field ground motion records were performed to develop fragility functions for nine squat RC shear walls with normal- and high-strength materials at different damage states. These damage states were characterized by several performance indicators following relevant guidelines. The current study identified wall damage states based on (1) yielding of reinforcement bars, concrete crushing, shear failure, and reinforcement buckling/fracturing; and (2) crack widths (i.e., 0.5, 1.5, and 3 mm) calculated using the modified compression field theory. Several wall design parameters, including material strength, reinforcement spacing and axial load level, were investigated to quantify their influence on the seismic fragility of such squat RC walls. Finally, the economic benefits of using high-strength materials in nuclear power plants were evaluated by presenting direct comparisons between the walls in terms of their total rebar weights and the corresponding total construction costs. The results showed that the use of high-strength concrete and high-strength reinforcement with large spacing between the rebars can lead to early cracking of their walls, thus having a higher probability of exceedance values to damage relative to walls designed with normal-strength materials. The results demonstrate also that enhancements in seismic fragility coupled with low total construction costs can be attained by walls with normal-strength concrete and high-strength reinforcement. The current study facilitates the adoption of RC shear walls with high-strength materials in nuclear construction practice.