Freyssinet International (stup)

Bruno Lancia

Bernard Basile

In order to measure in situ the residual tension F,of a pre-stressed bar braced between two anchorages, the two-way propagation time T,of an ultra-sonic wave between the two ends of the bar is measured, and F,is evaluated by the formula F,&equals;F,&plus;k,.(T,&minus;T,). 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 T,is determined as being the two-way propagation time measured for F&equals;0, the curve is approached in the neighborhood of the value F&equals;0 by a first straight line of slope k,, an upper portion of the curve is approached by a second straight line of slope k,, the constant F,is determined as being the traction effort F corresponding to the point of intersection of the first and second straight lines, and the constant k,is determined according to the relationship,/k,&equals;(,/k,)&minus;(,/k,).

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Marseille, France

Bruno Lancia