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Monitoring Of Cables With BRIMOS®

Tete suspension bridge, Mozambique Rosenbrücke Tulln, Austria Sancho el Mayor, Tudela, Spain bridge cables Strelasund, Germany

In principal a control of the acting cable force with a new application of the prestressing jack is possible, but this check is connected with a great logistic, time and therefore also financial expenditure. Furthermore there is the danger that unintended damages at the cables are caused. For this reason modern, non-destructive procedures present itself which are based on the dynamic characteristic.

The evaluation of the cable forces is done directly through the measurements of the fundamental vibration frequencies, as well as of the interval between the frequencies of consecutive modes.



acceleration sensor on bridge cable BRIMOS® Recorder measuring vibrations BRIMOS® Recorder measuring inside a box grinder measurements on cable bridges measurements on cable bridges measurements on cable bridges

For the calculation of the exact cable force the determination of the basic and higher vibration frequencies is necessary. A linear relation between the basic and higher order of natural frequencies is only valid for a wire without sag and bending stiffness. This theoretical case is called string wire. In such a string wire there is a harmonic succession of every mode shape starting from the first up the to very high natural frequencies.

A real cable brings up a deviation from this ideal case in the higher modes, since the bending stiffness causes an increase of natural frequencies in the higher modes. For an accurate hanger force measurement, this effect must be considered.


BRIMOS® cable analysis software BRIMOS® analysis viewing a vibration measurement file recorded by a BRIMOS® recorder

From the measurement data the actual hanger force can be calculated by the BRIMOS® Software. The only input needed for this analysis is the hanger geometry and the hangers properties. The determination of the natural frequencies, the bending stiffness, the damping values and the hanger forces is done full automatic by the BRIMOS® Software.

The identified eigegenfrequency f1 is a function of the effective hanger force, the length, the mass and the stiffness of the hanger.


The results of the analysis are:

  • Natural frequencies of the cables
  • Cable forces
  • Cable damping
  • Cable stiffness
  • Susceptibility to vibrations (wind-rain induced vibrations, parametric excitation by thebridge deck

Our measurement services inlclude:

  • Site visit of an experienced VCE engineer for the measurements.
  • BRIMIOS ® Recorder for the measurements.
  • Short visual inspection of the cables by the VCE engineer.
  • Performance of vibration measurements on each single cable with a sampling rate of 500 Hz in the total length of 330 sec.
  • Quality check of the measurement data on site.
  • Data analysis in the home office with the BRIMIOS ® software
  • Determination of the cable forces, cable bending stiffness and cable damping.
  • Preparation and submission of a detail assessment report with the determined dynamic properties and cable forces for all cables.




the BRIMOS® Recorder with equipment
BRIMOS® Recorder with equipment