Experimental Study of Passive Seismic Vibration Isolation by Periodic Barriers

Date
2022-08-09
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Abstract

Seismic vibrations are a significant threat to structural stability and serviceability. Due to changes in geological conditions, earthquakes have become common and more intense in vibration. The damages that occur due to earthquakes can be devastating, often irreparable, and unserviceable. Critical infrastructures need to be protected from seismic vibrations to mitigate earthquake damage. However, no effective seismic isolation system works well for different seismic vibrations and structures. A seismic isolation system is a method to protect structures that acts as a decoupling system to the structure, which aims to uncouple the motion of the structure from incoming waves by reducing the kinetic energy of vibration transferred to structures. A wave barrier combining the advantages of trench-type wave barriers and metamaterials is made by infilling the trench-type wave barrier with metamaterials. This research aims to study and propose a non-invasive vibration isolation system using periodic barriers. A series of full-scale field experiments are conducted to investigate the screening effectiveness of both empty trench and periodic barriers. The precast 1D unit cell periodic barriers are arranged to form one long barrier with a length of 8 ft, one short thick barrier with a length of 4 ft and width of 1.84 ft, and two short barriers with a length of 4 ft to examine the influence of barrier length and the number of unit cells on the vibration isolation performance. The triaxial (T-Rex) shaker truck generates excitation in the vertical, horizontal inline, and horizontal crossline directions. Three excitation inputs are tested, including fix-frequency harmonic, frequency sweeping, and earthquake excitations. Before the installation of the barrier, a benchmark test is performed. Each geophone sensor position records the ground surface response in all three directions. The responses in front of the barrier and behind the barrier, the normalized responses, and the frequency response function (FRF) are all provided and discussed in detail. Test results show that the various excitation inputs are comparable and similar results. It is found that the excitation directions influence the periodic barrier's effectiveness because of the dominant waveform. The screening effectiveness of periodic barriers can be determined in particular frequency ranges by comparing the FRF between the benchmark case and the case with periodic barriers. These frequency ranges are expected to be the periodic barriers' frequency band gaps. When the incoming wave frequency falls in this frequency band gap, the periodic barrier can isolate the vibration propagating towards the protected region.

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Keywords
Periodic barrier, T-Rex Shaker, Excitation frequency, Excitation Direction, Frequency Response Function, Frequency Band Gap
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