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Tension Assessment of Bridge P-T Bars Using Taut Cable Vibration Measurement (TCVM) Method

The taut cable vibration measurement (TCVM) method determines the existing tension in taut flexible cables through vibration testing based on cable theory. The TCVM method was recently used to assess tension forces in 416 posttensioning (P-T) bars on nine different bridges in Maryland. These included 336 P-T bars for retrofitting cracks in the hammerhead-shaped reinforced concrete pier caps of seven multi-girder bridges and 80 P-T bars for retrofitting cracks at pin connections of two steel rhomboid girder bridges. Since no literature was available on application of the TCVM method for P-T bars, especially considering the grout-filled double PVC sheathing corrosion protection system on them, field calibration tests were performed to validate its suitability and accuracy. It was found that the TCVM method is able to estimate the existing tension in the P-T bars with an accuracy of within 5%. This paper discusses the concept of TCVM, its application for tension assessment of bridge P-T bars, special considerations for the fast fourier transform (FFT), results of the calibration test, and a recommended procedure.

1. Kim, B.H. and T. Park. “Estimation of cable tension force using the frequency-based system identification method,” Journal of Sound and Vibration 304 (660–676). 2007. 2. Cable Force Measuring System, Bridge Diagnostics, Inc., Boulder, CO. 2006.
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