Natural Frequencies of Model Piers under Different Ground Support Conditions

Abstract

The natural frequency is critical for evaluating the integrity of bridge piers. However, the natural frequency of bridge piers can vary with the support condition of the ground. The aim of this study is to investigate the natural frequency of bridge piers under different ground conditions and at different embedded depths using a small-scale concrete pier. The model piers were fixed to asphalt concrete pavement using epoxy to simulate the rock site condition. Furthermore, model piers of different embedded depths were installed in a soil chamber with dimensions of 1.0 m × 1.0 m × 0.5 m to simulate weathered soil conditions. The upper part of the model pier was hit with a hammer having a rubber tip, and the acceleration signals were measured using three accelerometers installed at the upper, middle, and bottom parts of the model pier. Fast Fourier transforms were performed to analyze the natural frequencies of the model piers. The experimental results showed that the natural frequency under the fixed condition using epoxy was significantly higher than that under the unfixed condition. In the case of weathered soil conditions, three peak points appeared in the frequency domain. The natural frequencies measured at these three points increased with the embedded depth. The increment ratio of the natural frequency with the largest amplitude was significant. This study demonstrates that ground support conditions should be considered when evaluating the integrity of bridge piers through natural frequency analysis.