Wykeham Farrance’s Resonant Column to evaluate Shear Modulus and Damping Ratio Sponsored

Wykeham Farrance’s Resonant Column is a versatile system that combines Resonant Column and torsional shear tests into one convenient device allowing you to determine the following:

• RC: damping ratio from half power bandwidth, free vibration data and white noise
• TSS: damping ratio from hysteresis loops

• current-driven motor that applies torsional load to the sample
• a series of transducers with signal conditioning
• cell and back pressure electro-pneumatic control system
• data logger.

How it works

• A cylindrical soil specimen is restrained at the base and dynamically excited at the top by means of an electrical motor generating torsional forces via eight drive coils encircling four magnets attached to a drive plate at frequencies of up to 300 Hz
• The fundamental mode of vibration is determined from the maximum amplitude of motion. Following test standard ASTM D4015, resonant frequency, shear wave velocity and shear wave modulus are calculated using elasticity theory.
• The corresponding shear strain is evaluated from the motion amplitude. Material damping can be determined from the half-power bandwidth or from a free-vibration decay curve, which is generated by shutting off the driving power.
• In the Torsional Shear test, the soil specimen is deformed cyclically at a low frequency (a maximum of 10 Hz), whilst continuously monitoring torque and deformation.
• From the torque-deformation curves, a relationship between average shear stress and average shear strain is obtained, which in turn provides the shear modulus and the damping ratio.