The 2D shaker is designed to conduct more realistic in-flight earthquake simulations, where the base of the 2D laminar box container with the model is subjected to two prototype horizontal components of earthquake shaking. The significance of two-dimensional shaking in causing higher densification in dry sands and excess pore pressures in saturated sands as compared with 1D shaking has been shown by many cyclic loading experiments on soil. Two-dimensional shaking is also important to clarify the relationship between ground surface slope and direction of shaking, for a number of geotechnical phenomena involving permanent deformations.
The 2D shaker can apply shaking to centrifuge models in the prototype horizontal plane while being spun at up to 100 g. A wide variety of motions can be produced with the shaker, including 1D and 2D acceleration time histories comprised of periodic, aperiodic, random, or scaled earthquake signals. By mounting the 2D laminar box or another suitable centrifuge model container to the shaker slip-table, the shaker can provide dynamic excitation to soil models and thereby facilitate investigation of the behavior of scaled geotechnical or soil-structure systems in response to these complex excitations. When not used for providing base input motions for dynamic testing, the shaker can be used to support static model containers for tests of up to 150 g.
|Method||Servo-hydraulic multi-actuator system|
|Shaking Type||Periodic or random,
determined by input signal
|Shaking Direction||Two prototype horizontal directions|
|Force||11,000 pounds (49kN) each axis|
|Max. shaking velocity||45 in/sec (1.1 m/s) each axis|
|Max. Table Displacement||0.50 in (12.2 mm) each axis|
|Max. Payload Dimensions
(L × W × H)
|38 in × 26 in × 28 in
(965 mm × 660 mm × 711 mm)
|Max. Payload Weight||550 pounds (250 kg)|
|Max. Centrifugal Acceleration||100 g|
|Stroke||1.00″ peak to peak (25.4 mm)|
|Overhead Clearance||10,000 mm|
|Maximum mass (reduced performance)||700 kg|
|Nominal max at maximum performance||300 kg|
|Mounted on a centrifuge|
|Maximum centrifugal acceleration||100 g|
|X (horizontal axis)||25.4 mm|
|Y (2nd horizontal axis)||25.4 mm|
|Maximum Velocity of Table Surface Center|
|X (horizontal axis)||1100 mm/s|
|Y (2nd horizontal axis)||1100 mm/s|
|Maximum Frequency of Table|
|X (horizontal axis)||350 Hz|
|Y (2nd horizontal axis)||350 Hz|
|Maximum Actuator Capacity|
|X (horizontal axis)||49,000 N|
|Y (2nd horizontal axis)||49,000 N|
The SignalStar Matrix is a unique combination of hardware and software specifically designed to control multi degree of freedom vibration systems. The RPI 2D shaker table is free to move in three degrees of freedom (X,Y,Θ) and therefore requires a minimum of three inputs to control the system. The table is driven by three hydraulic actuators, two in the X direction and one larger actuator in the Y direction. Accelerometers are usually placed coaxially with each actuator, providing excellent control of the individual actuators. However, most researchers would prefer that the peak ground acceleration of the geotechnical model be controlled, and the matrix is capable of controlling the system from accelerometers placed anywhere in the model. The researcher is free to control their experiment from accelerometers mounted on critical structures within their model design, accelerometers within the soil structure, or most commonly at the base of the soil container. This allows the researcher to control the input to the model exactly, and completely eliminates the influence of external vibration sources.
The matrix software will iteratively correct the actual response of the model to eliminate any distortion of the desired motion. Corrections can be made in both the time and frequency domain. Corrections in the frequency domain will cancel out nonlinearity in the shaker hydraulics, as well vibrations of the table, centrifuge, basket, and model container. Time domain Corrections compensate for hydraulic pressure fluctuation during long or large amplitude shakes. This allows the user to maintain precise control over the amplitude for long cyclic or earthquake motions. The system will converge on the correct solution in a small number of iterative solutions, learning the behavior of the system and adjusting with each iteration.
The user interface of the software is simple and easy to use, and allows the researcher to use completely independent acceleration signals for each actuator. This allows earthquake replication with unique N-S and E-W accelerations to be studied. The matrix software will actively identify crosstalk between the signals, and eliminate it from the opposing direction. For example, if you were to shake 50hz in the X direction, and 30hz in the y direction, the shaker would actively eliminate all unwanted 30hz content in the X direction. The final solution will be an exact replication of the desired motion with no crosstalk or distortion.