Development of rocking constraint device with vertical damping capacity for three-dimensional base-isolated frame structures

A new rocking constraint device(RCD)is developed for three-dimensional(3D)base-isolated frame structures by connecting a custom-designed cylinder pair to provide vertical damping with replaceable damping components installed outside the cylinders when the superstructure undergoes translational motion,and rocking constraint capacity when the superstructure is susceptible to rocking.Theoretical formulas for calculating the damping and rocking constraint stiffness of the RCD are proposed.Two series of sinusoidal loading tests are conducted at different loading frequencies and amplitudes to verify the damping and rocking constraint performance of the RCD.The test results show that the cylinder without orifices on its piston can provide the desired damping with a replaceable damping component,and that the RCD can effectively suppress rocking.Although the vertical stiffness of an individual cylinder is affected by the location of the replaceable damping component and loading frequency,the average vertical stiffness of the two cylinders,which determines the rocking constraint stiffness of the RCD,is independent of the two factors.Comparisons of the test and theoretical results indicate that the errors of the proposed formulas for calculating the damping and rocking constraint stiffness of the RCD do not exceed 12.9%and 11.0%,respectively.

H_(∞)control in the frequency domain for a semi-active floor isolation system

A floor isolation system installed in a single floor or room in a fixed base structure is designed to protect equipment.With this configuration,the input motions to the floor isolation from the ground motions are filtered by the structure,leaving the majority of the frequency content of the input motion lower than the predominant frequency of the structure.The floor isolation system should minimize the acceleration to protect equipment;however,displacement must also be limited to save floor space,especially with long period motion.Semi-active control with an H_(∞)control was adopted for the floor isolation system and a new input shaping filter was developed to account for the input motion characteristics and enhance the effectiveness of the H_(∞)control.A series of shake table tests for a semi-active floor isolation system using rolling pendulum isolators and a magnetic-rheological damper were performed to validate the H_(∞)control.Passive control using an oil damper was also tested for comparison.The test results show that the H_(∞)control effectively reduced acceleration for short period motions with frequencies close to the predominant frequency of the structure,as well as effectively reduced displacement for long period motions with frequencies close to the natural frequency of the floor isolation system.The H_(∞)control algorithm proved to be more advantageous than passive control because of its capacity to adjust control strategies according to the different motion frequency characteristics.