Drive Plate Mass Polar Moment of Inertia in Stokeo Type Resonant Column Devices

The calibration procedure employed by researchers at the University of Arkansas (UA) to calibrate two Stokoe-type resonant column torsional shear (RCTS) devices is presented herein. Specifically, the development of a device-specific calibration process to determine the mass polar moment of inertia of the RCTS drive plate assemblies (J0), as a function of frequency, is described. Three aluminum calibration specimens and three stainless steel masses with known geometric and material properties were utilized to experimentally determine the J0 values. Experimental data collected by researchers at the University of Arkansas and obtained from other sources (Utah State University, the University of Texas at Austin, the University of Colorado at Boulder, the University of Southampton, Rensselaer Polytechnic Institute, and Kleinfelder) were analyzed utilizing two different data reduction methods. Key findings include the J0 values for two UA drive plates (2.743∙10-3 kg∙m2 and 2.750∙10-3 kg∙m2 for Devices 1 and 2, respectively) and fitted calibration functions for J0, as a function of frequency, for multiple RCTS devices. For samples with low natural frequencies (less than 100 Hz), the frequency dependence of the mass polar moment of inertia was determined to have negligible effects (less than 1.1 percent) on the calculated shear wave velocity for dry Ottawa sand.