A dynamic analysis of the stored angular momentum actuator used with the equivalent shear beam container

Cambridge University has used several systems to induce earthquake like shaking into soil models. Most recently, the development of the Stored Angular Momentum (SAM) actuator used with the Equivalent Shear Beam (ESB) model container in the Schofield Geotechnical Centrifuge Centre proved to be a promising new tool for centrifuge earthquake studies. A larger version of this system has been designed and constructed for the US Army Centrifuge in Vicksburg, Mississippi. This unit can shake specimens up to 0.6m in height and provides users the opportunity to investigate the dynamic behaviour of deep foundations. Initial use of the SAM-ESB concept in Cambridge has demonstrated its potential as a new and practical method of centrifuge earthquake modelling. This investigation studies the dynamic response of the shaking system and its interaction with the soil specimen. The purpose of the research is to improve the quality of the shaking motion applied to the model through a deeper understanding of the mechanical aspects of the shaker design. This is carried out by a preliminary dynamic analysis of the Cambridge SAM-ESB system. Due to the complexity of the centrifuge earthquake data (i.e. non-linear and non-stationary behaviour), new time-frequency analysis techniques using harmonic wavelets are introduced. Results achieved in Cambridge are used to aid in the development of the new larger version for the US Army Centrifuge. The new, larger WES SAM-ESB system is evaluated using many of the previous dynamic analysis techniques. Calculations and experiments demonstrate that the WES-ESB container constructed in 1997 is not as stiff as intended and is limited for use with a small range of models. It is recommended that future ESB containers are built with a high fundamental natural frequency and then tuned to match the dynamic response of softer models by the addition of mass.