Vibratory signature of electric pylons under impulse testing

A nondestructive vibratory technique has been used to record the vibratory signature of electric pylons. It evidences the principal modes of vibrations. The vibration magnitude depends on the impact location and the loading amplitude. The appearance of energy dissipation mechanisms, corresponding to a damaging process, is readily detected by a change of characteristics of the recorded acceleration signals. A method based on Volterra series provides a ready mean to analyze the nonlinear response and permits us to monitor the durability of the pylon in service. The presented technique relies on the evaluation of a scalar called `nonlinear contrast,' indicating the significance of nonlinear behavior of the structure under impact loading, in comparison with a reference state. The calculation requires the identification of Volterra kernels through a multi-amplitude procedure. The fact that an unscrewed bolt has been evidenced shows that this technique is very sensitive. The second major experimental result is that the nonlinear contrast appears to be independent on the accelerometer location and direction.