EFFECTS OF TENSILE LOADING ON THE PROPERTIES OF ELASTIC-WAVE PROPAGATION IN A STRAND

Effects of tensile loading on the properties of longitudinal-mode elas tic-wave propagation in a 1.52-cm-diam, seven-wire strand used for pre stressed concrete structures were investigated experimentally. In an u nloaded state, the wave propagation properties in strand matched those seen in individual wires comprising the strand, namely, straight cent er wire and helical outer wires. In the strand, however, extraneous si gnals were found to be produced from the propagating wave due to physi cal interactions between the adjacent wires. Under tensile loading, it was observed that a certain portion of the frequency components of th e wave became highly attenuative and, thus, absent in the frequency sp ectrum of the wave. The center frequency of this missing portion, call ed notch frequency, was found to increase linearly with logN, where N is the applied tensile load. In addition, on both sides of the notch f requency, the wave exhibited a large dispersion in a manner similar to the behavior near a cutoff frequency. Possible causes of the observed behavior under tensile loading are discussed. (C) 1998 Acoustical Soc iety of America.