Filtering characteristics of isolation layer in base-isolated structures and shaking table test verification

Area of Science:

• Seismology and Earthquake Engineering
• Structural Dynamics
• Civil Engineering

Background:

• Base-isolated structures are crucial for critical infrastructure, but current seismic design methods struggle with long-period structures.
• Existing response spectrum methodologies have limitations in accurately assessing seismic actions for base-isolated systems.

Purpose of the Study:

• To analyze the seismic filtering characteristics of isolation layers in base-isolated structures.
• To propose and validate the use of a filtered response spectrum (FRS) for more rational structural design.
• To address the limitations of conventional design response spectra (DRS) for long-period structures.

Main Methods:

• Developed a two-degree-of-freedom (2DOF) model incorporating non-proportional damping of isolation bearings.
• Performed spectral analysis on original and attenuated ground motions to understand isolation layer filtering.
• Conducted shaking table tests using white noise and seismic excitations to verify theoretical findings.

Main Results:

• Shaking table tests confirmed significant filtering effects, reducing acceleration time-histories to 1/3-1/2 of original peak values.
• The filtered response spectrum (FRS) showed reduced peaks, rightward shifts, and shortened platform segments compared to DRS.
• Theoretical and experimental results validated FRS as a more rational design basis than conventional DRS.

Conclusions:

• The filtering principle of isolation bearings is key to their effectiveness, especially for long-period structures, surpassing simple period elongation.
• Current seismic design codes inadequately represent the filtered seismic input experienced by base-isolated structures.
• Revisions to design codes are needed to include isolation-specific filtered spectra for rational and resource-efficient seismic design.