Force Measurements on Flexible Sagged Cable Undergoing Forced Vibration at a Single Point

Force measurements using load cell are carried out at one suspension point of a horizontal sagged cable periodically excited at given amplitude and frequency at the position of 0.25 times the spanwise length of the structure measured from the load cell. The excitation amplitude is fixed at 1 mm and the steady excitation frequency is varied between 5 Hz and 70 Hz. Two response types have been identified. For excitation frequency values below approximately 50 Hz the longitudinal and vertical forces have frequency components at the whole number multiples of the excitation frequency. In contrast, at high excitation frequency values, i.e., above 50 Hz, a low-frequency component that is significantly lower than the excitation frequency also occurs. For such cases a transient time domain is identified in the spectrograms of the force components. Within this interval the instantaneous frequency spectra dynamically changes. It was shown that the width of the transient domain is affected by the time rate change of the excitation frequency.