Effect of damping on torsional-flexural frequencies of monosymmetric thin-walled beams scanned by moving vehicles

Abstract

This paper investigates the effect of damping on the torsional-flexural frequencies of monosymmetric thin-walled beams via the scanning by a single-axle test vehicle. A bi-directional damping model is adopted to account for the vertical and torsional-flexural motions of the beam, as they are mechanically uncoupled. To start, the closed-form solutions are derived for the vehicle, the beam and the vehicle-bridge contact responses. Based on the hypothesis of rigid cross sections, the rocking contact response is derived, which enables the torsional-flexural frequencies of the beam to be separated from the vertical ones. Both uniform and bi-directional damping properties are considered for the beam. The pollution effect of pavement roughness is overcome by using the residual contact response generated by two connected single-axle test vehicles. Through the parametric analysis, it is confirmed that: (1) the rocking contact response enables the first few torsional-flexural frequencies to be separately retrieved; (2) the damping ratio in each direction only affects the detectability of the frequencies, especially those of the high modes, in that direction for monosymmetric cross sections; (3) the residual contact response exhibits some robustness in identifying the frequencies of thin-walled beams with surface roughness and environmental noise effect; (4) a test vehicle moving in the side lane (with larger eccentricity from bridge's centerline) at a speed of 10 m/s (36 km/h) is recommended for the field test.