Flexural wave impulse response evaluations of piles using multiple triaxial acceierometers

A flexural wave impulse response approach is particularly applicable in the nondestructive evaluation of foundations of overwater structures, such as bridge piers or wharves, that lack access to their tops. The experimental procedure of the flexural wave impulse response method is similar to that of the traditional (longitudinal wave) impulse response method. In order to pre-verify the possibility of integrity testing on a single newly constructed pile bent, the transient-state flexural waves are induced by lateral impact and recorded by three triaxial accelerometers equidistantly mounted to a model concrete pile side. The frequency-based analysis used in the conventional impulse response testing cannot cope with the flexural wave impulse response testing due to its dispersive characteristics at low frequencies. Using the resonance solutions and flexural mode guided wave prediction curve is a simple and efficient method of finding the resonant frequency and phase velocity when knowing pile diameter and flexural wave impulse response results. The vibration responses in the radial and axial direction are measured at the impact position (position 0°). The angular/tangential direction responses are also analyzed at position 90° away from the impact position. These phase velocities measured at resonant frequencies have good matches with the theoretical flexural mode wave predictions at frequencies below 4,000 Hz. The testing results also indicate that the resonance characteristics of flexural waves traveling in a pile are not dependent on measurement positions but the engineering properties and geometrical characterization in the concrete pile.