Equipment
1D Shaker
RPI’s large 1D shaker is a servo-hydraulically controlled system designed to produce 1D (horizontal) shaking in response to an applied input voltage signal. It is designed for use with medium-sized (or larger) geotechnical centrifuges, for studies in which application of input motions to the base of a model container is desired. Maximum design shaking force is 18,000 lbf at a supply pressure of 3,000 psi, the maximum stroke (i.e., peak-to-peak displacement of the slip-table) is 1.25 inches. The nominal operating frequency range is 20-600 Hz.
The shaking force is developed within the hydraulic actuators and is applied between the actuators, which are fixed to the platform of the centrifuge, and the slip-table, to which the model container is attached. Feedback signals are derived from:
- the position of the slip-table
- the internal state of the servovalves
- the force (pressure) developed by each actuator
These signals are compared to the applied input signal within the servocontroller to produce an actuating or error signal. This error signal is amplified (Team model 1528 power amplifiers) and the resulting high current used to drive the voice coils in the pilot stage servovalves (Team model V-20). A second, high flow slave-stage valve (Team model V-750) acts as a hydraulic amplifier, converting the tiny flow produced by the V-20 valve into the large flows needed to supply the actuators.
| Method | Servo-hydraulic multi-actuator system |
| Shaking Type | Periodic or random, determined by input signal |
| Shaking Direction | One prototype horizontal directions |
| Nominal shaking force | 11,000 pounds (50 kN) |
| Max. shaking velocity | 45 in/sec (1.1 m/s) |
| Max. Table Displacement | 0.25 in (6.35 mm) |
| 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) |
| Nominal Shaking Frequency | 0–350 Hz |
| Max. Centrifugal Acceleration | 100 g |
Images
2D Shaker
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.
For more information, please read our overview.
| Method | Servo-hydraulic multi-actuator system |
| Shaking Type | Periodic or random, determined by input signal |
| Shaking Direction | Two prototype horizontal directions |
| Nominal shaking force | 11,000 pounds (50 kN) each axis |
| Max. shaking velocity | 45 in/sec (1.1 m/s) each axis |
| Max. Table Displacement | 0.25 in (6.35 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) |
| Nominal Shaking Frequency | 0–350 Hz |
| Max. Centrifugal Acceleration | 100 g |
| Table Size | |
| Length | 965 mm |
| Width | 900 mm |
| Overhead Clearance | 10,000 mm |
| Payload Mass | |
| Maximum mass (reduced performance) | 700 kg |
| Nominal max at maximum performance | 300 kg |
| Shaker Characteristics | |
| Mounted on a centrifuge |  |
| Maximum centrifugal acceleration | 100 g |
| Peak-to-Peak Stroke | |
| X (horizontal axis) | 6.35 mm |
| Y (2nd horizontal axis) | 6.35 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) | 50,000 N |
| Y (2nd horizontal axis) | 50,000 N |
Control System
The control of the 2D shaker is provided through a combination of hardware and software.
Hardware Control
The hardware portion of the control system is comprised of:
- Solenoid valves and feedback transducers for control and monitoring of the hydraulic supply, supply and return accumulators, and hydrostatic pad bearings;
- The servocontroller, power amplifiers and associated feedback transducers for implementing the actuator servo control loops;
- A dedicated shaker control server computer.
Software Control
The software portion of the control system will be based upon the multi-input, multi-output control program developed by PVL, which will allow for several functions including:
- Automatic sequencing of the hydraulic controls, provided to pressurize the shaker without “thumping” the sensitive centrifuge model, then apply the shaking signals, and finally shut down the shaker in a smooth and controlled fashion.
- Monitoring and recording control signals within the servoloops themselves, including slave spool and slip table feedback signals, derived error signals, and control signals. Using this information, the performance of the shaker system can be routinely monitored. In case of faulty operation, the recorded data can be accessed by the manufacturer and faults can potentially be diagnosed via the Internet.
- Exciting centrifuge models using calibrated shaker input signals, uncalibrated signals such as fixed frequency sinusoids or other analytic signals, pseudo-random signals, or arbitrary waveforms.
- The control software is implemented as a client-server application using a fiber optic LAN for remote communication.
