Investigation of Inelastic Higher-Mode Effects in an RC Structural Wall under Long-Duration Ground Motion Using Hybrid Testing

Reinforced concrete shear walls (RCSWs) constitute the primary seismic force-resisting system for mid-rise and high-rise buildings in western North America. Numerical analysis has indicated that large-magnitude, long-duration earthquakes, such as those generated by the Cascadia Subduction Zone (CSZ), can induce multiple amplified shear cycles due to inelastic higher-mode effects, raising concerns about brittle failure in RCSWs. This study presents a large-scale substructuring pseudodynamic hybrid test on a 10-story ductile RCSW to experimentally evaluate inelastic shear amplification and seismic performance during an intense, long-duration subduction earthquake. The first story of the wall was tested as an experimental substructure using a scaled, heavily instrumented specimen, whereas the remaining stories were modeled nonlinearly as unscaled components via numerical methods. The results revealed an inelastic shear amplification factor of 2.43, significantly exceeding the maximum values recommended by the current seismic design codes. Ductile shear failure accompanied by flexural yielding was observed. The conservative approach to calculating the design shear resistance ensured that no diagonal concrete crushing occurred. The findings also highlight the considerable impact of higher-mode effects, including amplified shear forces, the increased contributions of shear deformation, and the out-of-phase interactions between flexural and shear responses.