Document Type : Research Article
Authors
1
M.Sc. Graduate, Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
2
Associate Professor, Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran,
Abstract
Using shaking tables in experimental studies on buildings or other installations subjected to earthquake actions
are considered inevitable in many circumstances. Due to their unique abilities in simulating ground motion effects
on prototype systems, such facilities can provide the researcher with the most accurate and sophisticated results on
the role of earthquake actions on the specimen under investigation. However, providing accuracy in ground motion
simulation for shaking tables needs careful attention to its subsystems and dynamic interaction between them
(specimen, table, actuators, control system and the foundation). In fact there is the possibility of a strong interaction
between the shaking table itself and the specimen under investigation depending on its weight and frequency
contents. Interaction between the table and its foundation assembly can also be considered important in certain
cases. In addition, during shaking tables operation some vibrational force and energy can be transferred to its
surrounding environment and causes undesirable effects in the nearby buildings. In this case, vibration isolation for
the foundation of shaking table can partially solve this problem. However, it may also intensify the interaction
between the table and its foundation that needs to be addressed properly to maintain the accuracy of the system in
ground motion simulation. In this work a simplified model for investigation on the role of vibration isolation on
foundation of shaking table assembly is proposed that takes into account the interaction problems among all
subsystems of shaking tables. A large number of time integration analysis subjected to actual earthquake records
(applied in the table’s degree of freedom) have been carried out on this model. According to the results of this study,
vibration isolation on a 4000 tons foundation of a typical middle size shaking table (6 by 6 meters in size with the
weight of 40 tons) reduces, on average, the level of maximum acceleration transferring to the ground to about 1/3
of that for the non-isolated system. This has happened in the expenses of about ±3 mm maximum lateral
displacement for the foundation with respect to the ground. However, the results in this case also signifies sensible
changes in the actuator’s force, stroke and frequency demands that have to be provided to meet the required
accuracy in the ground motion simulation. In addition, according to the results of this study the dominant frequency
of vibration that transfers to the ground and the surrounding environment in case of non-isolated foundation is in the
range of 8 to 15 Hertz while in the isolated system a low amplitude dominant frequency exist within the range of 5
Hz. Such results vary with the change in the mass and natural frequency of the specimen subsystem. According to
these results vibration isolation for the foundation of shaking table is quite effective in reducing vibrational effects
transferring to the surrounding environment and nearby buildings. On the other hand, using vibration isolation
technique in design process for foundation of shaking tables may require a major upgrade in the technical specifications for actuators of the table and a need for more sophisticated control system hardware and its add-on
algorithm and software.
Keywords
Main Subjects
)