| 摘要 |
In order to measure in situ the residual tension F1 of a pre-stressed bar braced between two anchorages, the two-way propagation time T1 of an ultra-sonic wave between the two ends of the bar is measured, and F1 is evaluated by the formula F1=F0+kb.(T1-T0). During a preliminary calibration carried out without demounting, the bar is subjected to a variable traction effort F. For each value, the two-way propagation time T of an ultra-sonic wave between the two ends of the bar is measured, a curve associating the effort F with the time T is recorded, and the constant T0 is determined as being the two-way propagation time measured for F=0, the curve is approached in the neighborhood of the value F=0 by a first straight line of slope ka, an upper portion of the curve is approached by a second straight line of slope kL, the constant F0 is determined as being the traction effort F corresponding to the point of intersection of the first and second straight lines, and the constant kb is determined according to the relationship 1/kb=(1/kL)-(1/ka).
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