Seismic Hybrid Testing of Two-Story Low Aspect Ratio RC Shear Walls with Different Configurations in Nuclear Facilities

Low-aspect-ratio reinforced concrete (RC) shear walls are widely used as a seismic force-resisting system in containment and safety-related nuclear facilities. However, there has been limited research to date that experimentally quantified the performance of such nuclear RC shear walls when subjected to different ground motion levels. This lack of study is mainly attributed to the significant challenges that most laboratories encounter when such walls are tested, especially in a multistory setting, such as specimen sizes, actuator capacities, space limitations, and the ability to simulate the large mass associated with nuclear facilities. To address this, the current study experimentally investigates the seismic performance of two two-story low-aspect-ratio nuclear RC shear walls with different configurations (i.e., namely, walls W1-R and W2-B) using the hybrid simulation testing technique. Wall W1-R was designed to have a rectangular cross-section, while wall W2-B has boundary elements with increased thicknesses at the wall ends. Both walls were designed to have similar shear and flexural capacities to allow for direct comparisons. The walls were then tested under different ground motion levels, ranging from operational to design and beyond-design earthquake levels using a developed hybrid simulation framework. The experimental results of the test walls are presented in terms of their force-displacement responses, lateral and rotational stiffnesses, ductility capacities, rebar strains, crack patterns, and damage sequences. The results show that both walls exhibited similar force and moment capacities, crack patterns, and stiffness degradation trends. However, W2-B showed lower displacements and interstory drifts than those of W1-R during their design basis earthquake levels. The former wall had also higher ultimate lateral and rotational displacements than the latter wall at their beyond-design basis earthquake levels, which indicated enhanced ductility capacities when boundary elements were used in W2-B. In addition, the results show discrepancies between the theoretical and experimental lateral and rotational stiffness values, thus highlighting the need for distinct rigidity reduction factors for low-aspect-ratio RC shear walls in future editions of relevant nuclear design standards. The current study enlarges the experimental database pertaining to the seismic performance of low-aspect-ratio RC shear walls with boundary elements to facilitate their wide practical adoption in nuclear facilities.