The use of accelerometer based measurement techniques for evaluating bridge forced vibrations or to perform bridge modal analysis is well established. Some of the goals of this experimental approach and typical results are here reviewed. It is well known to all researchers who have experience in vibration measurements that values of acceleration amplitude can be very low at low frequencies and that a limitation to the use of accelerometer can be due to the threshold parameter of this kind of transducer. Under this condition the measurement of displacement seems more appropriate. On the other hand laser vibrometer systems detect relative displacements as opposed to the absolute measures of accelerometers. In this paper the results of some in field measurements on a highway little bridge, excited by traffic, under normal operating conditions, are analyzed. Vibrations have been measured simultaneously by a typical accelerometer for civil structures and by a laser vibrometer equipped with a fringe counter board in terms of velocity and displacements. The accelerations calculated from the laser vibrometer signals and the one directly measured by the accelerometer has been compared. The advantages of the use of a laser vibrometer at low frequency are relevant and it appears possible to open up new possibility to analyze bridge loads in operating conditions, monitoring bridge health state, predict fatigue life and improve the bridge design.

Date Published: 22 May 2000
PDF: 9 pages
Proc. SPIE 4072, Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, (22 May 2000); doi: 10.1117/12.386764

Published in SPIE Proceedings Vol. 4072:
Fourth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications
Enrico Primo Tomasini, Editor(s)