STS-CFA computes in-situ cable tension using the vibration of the cables collected through acceleration measurements. This software is often run side-by-side with STS-LIVE to enable field crews to quickly measure and adjust tension levels in stay, lift or counterweight cables. For example, a counterweight suspended by 12 parallel cables must have all the tension values balanced within a specified percentage of each other. Vibration measurements are obtained for each cable with BDI accelerometers connected to an STS4 system. STS-LIVE will record time-based vibration data as the user “activates” each cable with a rubber mallet. Upon completion of the vibration test, data from each accelerometer is immediately imported into the open STS-CFA window and processed. The CFA program will analyze each data history and display the results in the frequency domain for the user to quickly evaluate response quality and insure accurate results. Tension values are computed for each cable using the cables fundamental frequency and the user-defined physical properties (effective length & unit weight). Relative force differences and percent variations are provided to inform the crew how much each cable must be adjusted.
- Auto excitation detection, application can identify the moment the cable begins to vibrate and select the appropriate data range to be used in the FFT transformation
- Auto peak finding algorithm, application can automatically identify frequency peaks and calculate the fundamental frequency
- Easy-to-use graphical interface for verifying peak locations
- Cable properties can be input into the application for direct force calculation
- Output cable force data in spreadsheet format
- Balancing forces for bridge and lift gate counterweights by calculating the average force in multiple cables and displaying how much each cable is deviating from the average.
- Calculating cable forces in pedestrian and vehicle bridges
- Calculating cable forces in guy wires for radio towers, chimneys, and other cable-supported structures.
- Determining cable forces in tainter gate lift cables and other hydraulic structure cables.
Force measurements are based on the Taut Cable Vibration Method (TCVM). This process is limited to cables that can vibrate freely without obstruction and have relatively simple end-conditions. STS-CFA works best when the user has good estimates of the cable’s mass and effective lengths. Calibration procedures may be required to achieve accurate tension values when large connectors are present or for rods with flexural stiffness. However, cable force balancing can often be achieved by equalizing vibration frequencies when end-conditions and cable properties are identical. Note that STS-CFA can be run with other data acquisition systems as well.