Volume 33, Issue 5 (September 2010)
Calibration of Equipment Damping in a Resonant Column and Torsional Shear Testing Device
In a coil-magnet drive system of the resonant column (RC) and torsional shear (TS) apparatus, a back electromotive force (back emf) affects the measurement of stiffness and damping in soils. An empirical approach has been used to account for this problem; however, this approach is only applicable for a narrow range of conditions. This study focused on developing a method dealing with the back emf effect more precisely. The method proposed in this study is the use of an electromagnetic model to describe the back emf effect. This approach simplifies the problem by modeling the back emf in terms of an equipment spring constant (keq) and an equipment viscous damping coefficient (ceq). The electromagnetic model consists of four parameters. The method used to measure the model parameters and model verification is presented in this paper. The back emf effect on RC and TS tests can then be predicted. In addition, this study verifies that the equipment generated damping for the TS test is negligible.