Reduction of equipment-generated damping in resonant column measurements

Equipment-generated damping in the resonant column (RC) test due to interaction between the magnets and solenoids in the drive system causes a bias error in measured values of material damping ratio. Calibration and post-measurement corrections have been used to address this problem. In this study, an electromechanical model of the RC test is developed to aid in understanding the cause of equipment-generated damping and to identify possible real-time solutions. The model explicitly includes the signal source, which plays a key role in determining the amount of equipment-generated damping in the system. Furthermore, the model indicates that a current-mode source with large internal resistance rather than a more commonly used voltage-mode source is capable of reducing equipment-generated damping significantly in real time. A current-mode source is implemented using a voltage-to-current converter. The effectiveness of this approach is demonstrated using RC tests on aluminium, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and soil specimens.