Synopsis
A method of measuring the damping properties of concrete is described wherein the stress-strain or load-deflection hysteresis loop is electronically modified to make it easier to examine the loop or measure its area. The logarithmic decrement for concrete is typically about 0·05 (ranging from 0·03 to 0·15) giving a length: breadth ratio for the hysteresis loop of about 100:1. This is too elongated a figure to measure accurately or to study for loop characteristics. The electronic treatment is first to make the loop upright (i.e. parallel to the load axis) and then to amplify the width in the direction of deflection. Accuracy depends upon stable, accurate amplification, but this is not difficult for the structural frequencies of interest (< 5 Hz). The experimental techniques include the use of a very stiff, servo-controlled test machine to obtain accurate stress levels, frequency, waveform of loading, etc. and steel reference specimens are tested to eliminate machine errors. The method is claimed to be a significant step forward in the study of damping and is applicable to other hysteresis systems where the two parameters can be measured electrically.
