H/V Spectral Ratio Reveals Seismic Response of Base-Isolated Large-Span High-Rise in Beijing

This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing, as well as from a free-field station and roof frame, during a Mw 5.5 magnitude earthquake in Pingyuan, Shandong, in 2023. The H/V spectral ratio method was used to evaluate the structural dynamic response characteristics of the building and analyze the regulatory effect of the base-isolation layer on seismic waves. The results indicate that during the earthquake, the peak frequency of the free-field and the measurement points below the base-isolation layer was stable at 0.17 Hz, whereas the main frequency of the measurement points above the base-isolation layer increased to 0.75–1.18 Hz, which is 4–6 times greater than that of the points below. The amplitude was suppressed by more than 70%, confirming that the base isolation layer effectively isolated the low-frequency energy from the ground and increased the response frequency of the building. When the building was excited by an earthquake, a three-tier frequency gradient was formed throughout the building: “base-isolation layer (0.17 Hz)-main body (1.18 Hz)-roof frame (3.83 Hz)”, which can effectively avoid resonance of the entire building. In addition, the composite base-isolation device changed the dynamic characteristics of the structure. The resonance period was extended from 0.74 s (theoretical value without base isolation) to 5.9 s (calculated value), and the resonance frequency was reduced from 1.35 to 0.17 Hz. This finding indicates that the base-isolation layer can enhance seismic performance by increasing flexibility and damping.