A NEW METHOD FOR TORQUE FACTOR CALIBRATION OF COMBINED TORSIONAL SHEAR RESONANT COLUMN APPARATUS
BAI Lidong1，2，XIANG Wei2
(1. Faculty of Engineering，China University of Geosciences，Wuhan，Hubei 430074，China；
2. Guizhou Expressway Development Corporation，Guiyang，Guizhou 550004，China)
Abstract：Effects of torsional shear frequency，input voltage and specimen torsional stiffness on the torque factor are systematically investigated on the basis of a number of torsional shear tests on six aluminum calibration bars using the combined torsional shear resonant column apparatus. Results indicate that the torque factor of this type of device slightly decreases with increasing torsional shear frequency and input voltage，but significantly increases with increasing torsional stiffness of specimen，due to the inherent design limitation of the electromagnetic drive system. When the constant torque factor obtained from the traditional calibration method，which is suggested by the manufacturer，is employed to analyze the shear modulus of calibration bar，testing result is significantly underestimated with the error of 14% for the greatest stiffness calibration bar(Bar #6)，and overestimated with the error of 25% for the smallest stiffness bar(Bar #1). Therefore，a new calibration procedure is proposed to overcome the error induced by the inherent design weakness of the drive system. It can minimize the testing error within 3% for torsional shear tests conducted by this type of resonant column device.
SASANAKUL I，BAY J A. Calibration of equipment damping in a resonant column and torsional shear testing device[J]. Geotechnical Testing Journal，2010，33(5)：363-374.
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2012, Vol. 31 
