- Context
In the coming years, many bridges, tunnels, locks and viaducts are approaching their design life. This makes the proper planning of maintenance work very important, the most vulnerable objects must be done first, and budgets are limited. This requires a good understanding of the state of the structures. Traditionally, this insight is obtained by performing inspections or by locally installing sensors on the object, but both methods are labor intensive and expensive. Therefore other (non-contact) measurement techniques need to be evaluated and compared to find the best solution.
2. Equipment
The RSV-150 Remote Sensing Vibrometer is an optical vibration sensor, which measures the velocity or displacement at a certain point on the bridge. The vibrometer aims a laser beam at the structure so it can measure its dynamic response. If the structure vibrates, the Doppler effect will shift the returning light in phase and frequency. The outgoing and the returning signals are then compared using a laser interferometer, and the velocity of the vibration at a certain frequency can be determined. The displacement can be extracted directly from the phase shift of the of the Doppler effect.
3. Measurement Results
To perform the measurements, the sensor head was placed at the south end of the bridge and several points on the bridge were measured on in sequences of 5 to 10 minutes. On these positions, vibration sensors were also installed for comparison with the non-contact techniques.
The setup of the system is very simple. The sensor head is attached to the controller, and the laser beam can be pointed at the area of interest. When the sensor head receives enough laser light back to its detector, it directly starts measuring the vibrations.
When using laser vibrometry, the system only measures vibrations perpendicular to the direction of the laser beam. For this reason, the angle of the sensor head is measured and mentioned for every measurement. Afterwards the cosine error can be calculated, with this angle.
Konnexxions is also your consulting partner for non-contact vibration measurements. Don’t hesitate to contact us: we will analyse your needs and provide you with the right system.
