In this evaluatory study of means of measuring tension in prestressing stands for prestressed concrete, vibra-tension measurements were compared with strand tensions computed from strand elongation. The instrument works on the principle of the "vibrating string" formula T=4ML sup 2 F sup 2 where T is the strand tension, M is the mass per unit length of strand, L is the length of the vibrating strand, and F is the strand frequency of vibration. When certain settings peculiar to the size of the strand and the length of the vibrating strand are made on the Vibra-tension, the strand tension is a function of the frequency of the vibration of the strand. The procedure used in measuring the tension by elongation is described in an appendix. The repeatability of the vibratension measurements is excellent. The results (tabulated) show that the percent difference between the elongation measurements and the Vibra-Tension measurements ranged from t 7.6 percent to - 7.8 percent. The average percent difference for all 342 tests was - 0.62 percent. Of the 342 test comparisions, the percent difference was less than plus or minus 5 percent in 89.8 percent of the tests. The difference in principle between the 2 types of measurements are explained and it is shown that length measurement is more critical for the elongation method and is a factor in comparing the two methods. The Vibra-tension method is as accurate as the elongation method and a much more rapid test; it is recommended for adoption in less of the elongation method. It is advisable that readings on the tensioning jack gauges be recorded as a check on the operation of the Vibra-Tension instrument.

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: 21 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00097485
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-RD-76-S0442, HP&R 74
  • Contract Numbers: 930-069, 74
  • Created Date: Aug 13 1975 12:00AM