Experimental Determination of the Axial Force by Measuring the Eigen Frequency of a Straight Bar

Abstract

Based on the analytical correlation between the axial force on the straight bar with a constant cross-section and known boundary conditions and the dynamic parameters of its eigen frequencies, we analysed the possibility of experimental measurements of those parameters with the goal to relate them to the actual amount of axial force in the structural bar. Measurements were undertaken by means of the accelerometer and the associated equipment in laboratory and in real conditions. Laboratory tests on the etalon specimen confirmed the acceptable accuracy of the measurements compared with other means of measurement. Tests on the selected compressed members of the real structures did not confirm the accuracy realized in the laboratory. Small variations of material and geometric bar properties, together with uncertain boundary conditions of the real structural members influence the measurement accuracy and are not theoretically incorporated in the analytical expressions presented in this paper, making the proposed force determination method uncertain and not sufficiently reliable.