3.4.1 Development of shaking systems

Generating earthquake-like shaking of a model in flight on a centrifuge requires a power source or actuator. The actuator will be required high-frequency excitation and high force. If a model is constructed to a scale of 1/100, it must be subjected to a 100 G centrifugal acceleration, the frequency of input motion applied to the model must be 100 times those to which the prototype is subjected, the duration of shaking 100 times shorter, and accelerations 100 times larger.

Many kinds of shaking systems have been developed which include cocked spring system, small explosions, piezoelectric system, mechanical and hydraulic controlled systems. The common types of actuator in recent facilities are 1) piezoelectric system, 2) electro-magnetic system, 3) mechanical actuator system and 4) hydraulic actuator system.

In general, the piezoelectric system and electro-magnetic excitation system are especially good at producing high frequency variations in displacement, but not low frequencies. The mechanical actuator has the advantage of relatively low cost in manufacture and maintenance, being easy to operate and capable of generating sinusoidal vibration at a range of frequencies. The main limitation is the narrow frequency band. The primary advantage of the hydraulic actuator system is the adjustability in its input motion so that it can produce a range of different broader band input motions.

Zelikson, A., Devaure, B. and Badel, D. (1981) : Scale Modelling of Soil Structure Interaction during Earthquakes Using a Programmed Series of Explosions, Proc. of Int. Conf. on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, pp. 361-366.

Whitman, R.V. (1984) : Experiments with earthquake ground motion simulation, Proc. of Symp. on the Application of Centrifuge Modelling to Geotechnical Design, pp. 281-299.

Taylor, R.N. (1995) : Centrifuges in modelling: principles and scale effects, In Geotechnical Centrifuge Technology (ed Taylor, R.N.), Blackie Academic and Professional, Glasgow, pp. 19-33.