Novel vibration structural health monitoring technology for deep foundation piles by non-stationary higher order frequency response function

Damage in the precast concrete piles occurs mostly during installation. The wave propagation‐based nondestructive testing (NDT) is commonly used to estimate the effective length of the pile after installation and to detect pile damage. However, information extracted from this type of diagnosis is limited and subjective. Whereas, the vibration‐based NDT could provide a comprehensive automatic pile health diagnosis tool. In this paper, a new higher order vibration‐based health diagnosis technology, which utilizes a shaker to generate sweep‐sine excitation and an adaptive nonlinear non‐stationary higher order spectral analysis, is introduced for foundation piles. This research describes two different diagnostic technologies, namely, the advanced nonlinear non‐stationary chirp Fourier bicoherence (CFB) technology and the novel nonlinear non‐stationary frequency response function of the CFB (FRF‐CFB) technology. The CFB is a technology which is capable of quantifying the amplitude and phase coupling between harmonics of pile resonance oscillations caused by a damage. However, in practices, the amplitude and phase coupling between harmonics of pile resonance oscillations may be caused also due to the phase‐coupled harmonics of an interference imposed by an excitation source (e.g., shaker). Therefore, the novel diagnosis technology, FRF‐CFB, which detects nonlinearity caused solely by a structural damage, is proposed and implemented for real‐scale precast concrete piles. It is found that the FRF‐CFB technology successfully identifies the damaged piles. Finally, the diagnosis based on the conventional pile integrity testing, conducted on the same piles, is presented for comparisons with the FRF‐CFB technology and with the CFB technology.