Vibration Troubleshooting

Mode shape analyses of large structures such as bridges

• Natural frequencies for all detected eigenmodes
• Damping ratios for all detected eigenmodes
• Mode shapes for all detected eigenmodes

To perform this, the company Wölfel Engineering has used the RECOVIB Tiny to measure the bridge vibrations. Thanks to RECOVIB.Tiny, you no longer need to unwind meters of cables or install sophisticated wireless networks. (too long for Wi-Fi)
A shaker system is used for excitation of the bridge structure with two different orientations: in horizontal lateral direction and in vertical direction. 9 RECOVIB.Tiny are positioned on the bridge deck. Several measurements were recorded for both shaker configurations on both bridge sides. Based on broad band excitation measurements vibration data is evaluated: mode shape analysis is used to identify natural frequencies and damping ratios using curve fitting procedures from experimental modal analysis (EMA).

Mode shapes Analysis

The instrumentation campaign was able to identify the first four main resonance frequencies:  

• Rocking mode: 1.4 Hz
• Torsional mode: 1.9 Hz
• Bending mode (Horiz.): 3 Hz
• Bending mode (vert.): 4 Hz

For the purpose of carrying out this vibratory analysis on the footbridge, Woelfel Engineering chose to use the new vibration recorder, the RECOVIB Tiny, an extremely practical device for a fast and efficient vibration diagnosis.

Its wireless technology and intuitive operation provide substantial time savings in the performance of the measurements.

The RECOVIB Tiny is the only range of vibration and shock recorder that allows several sensors to be used simultaneously in a synchronized manner enabling the performance of modal analyses and operational deflection shape analyses on large structures such as this footbridge.