Enhancements and Verification Tests for Portable Deflectometers

Status:  Complete
Report Date:  12/16/2003


In this study, the accuracy of the stiffness estimate from portable deflectometers is investigated, based upon the example of a particular device, PRIMA 100. The Beam Verification Tester (BVT) apparatus was developed at the University of Minnesota for the Minnesota Department of Transportation to: (i) verify the performance of the PRIMA device and (ii) to check the calibration factors of the sensors of the PRIMA device. The objective of such tests is to detect the potential occurrence of deterioration of the sensorâ¿¿s accuracy. Associated with the BVT apparatus, an enhanced setup for the portable device is examined. The inconsistency of the traditional data interpretation method using peak values of load and displacement time histories is pointed out by comparing the stiffness estimated from the PRIMA device against the known stiffness of the beam. An alternative method using Frequency Response Functions, spectral average, Single Degree of Freedom System analog, zero frequency estimates and curve fitting is proposed to extract the static stiffness from PRIMA measurements. Test results show good agreement between estimates based on the modified analysis and true beam stiffness. Implementation of both the alternative data interpretation method and the enhanced device setup to quality assurance field measurements are proposed.

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