Patent ID: 6327912
Filing Date: 2001-12-11
Classification: G01L,G01N

Abstract:
A method for measuring in situ a residual tension F.sub.1 of a pre-stressed bar braced between two anchorages by determining a two-way propagation time T.sub.1 of an ultrasonic wave between two longitudinal ends of the bar and by evaluating the residual tension F.sub.1 by a formula of the form F.sub.1 =F.sub.0 +k.sub.b. (T.sub.1 -T.sub.0), where F.sub.0, T.sub.0 and k.sub.b are constants determined during a preliminary calibration carried out without demounting the bar, whereby the preliminary calibration comprises the steps of:subjecting the bar to different values of a traction effort F, applied in a zone situated outside of the interval between the two anchorages;for each value of the applied traction effort F, measuring the two-way propagation time T of an ultra-sonic wave between the two longitudinal ends of the bar, to memorize points of a curveassociating the traction effort F with the two-way propagation time T;determining the constant T.sub.0 as being the two-way propagation time T measured for a traction effort F=0;identifying on initial portion of said curve, in the neighborhood of the traction effort value F=0, by a first straight line having a slope k.sub.a ;identifying an upper portion of said curve by a second straight line having a slope k.sub.L ;determining the constant F.sub.0 as being the traction effort F corresponding to the point of intersection of said first and second straight lines; anddetermining the constant k.sub.b according to 1/k.sub.b =(1/k.sub.L)-(1/k.sub.a).