Tuned Liquid Damper with Rotatable Baffles to Control a 5-Story Structure Model under Near and Far-Field Earthquakes

Structural control is considered as an efficient method to improve seismic behavior of buildings. Control methods are divided into passive, active, hybrid and semi-active due to adaptability and need to external energy. Semi-active control methods have the reliability of passive systems, and at the same time maintain the consistency and variability of active systems. In this method, structural responses decrease based on the change in damping properties or stiffness of the system. Tuned Liquid Damper, TLD, has a dual operation: it can be used as a damper and water tank. It has low manufacturing, installation and maintenance costs. In this damper, water sloshing reduces the vibration of the structure. In the recent years, researchers have tried to use the baffles and perforated plates in the damper tank to increase the energy dissipation.
In this study, the variable baffles previously presented by Zahrai et al. are used. The objective is to examine the behavior of TLD with variable baffles and feasibility of its usage in semi-active control of structural responses due to near and far field earthquakes. Therefore, in this research, an experimental model of the proposed damper is used to passively control responses of a 2D frame. In this study, a benchmark 5-story building structure utilized in the Sydney Technological University, Australia and adopted by the International Association for Structural Control is used. The structure can have a maximum of five stories with different heights. According to the study by Zahrai et al. to tune the TLD, it is enough to adjust the structural frequency between the frequencies of the damper when the TLD baffles are fully open and fully closed concluding that the damper in this situation has the best performance. It should also be mentioned about the re-adjustment of the damper after rotation of baffles that since the period of the structure is between the damper periods in fully open and closed baffle situations, significant changes will not happen in initial tuning. In fact, if the TLD is tuned properly at first, the baffle rotation does not make too much change in its initial tuning. The study by Sun et al. is used to model the fluid damper in OpenSees. For each orientation, equivalent stiffness, mass and damping are determined. The mass and the viscous spring defined in OpenSees are utilized according to each baffle angle. The stiffness and damping of viscous spring are equal to the equivalent stiffness and damping values.
In this paper, the behavior of TLDs with variable baffles under four near-field and four far-field earthquakes is evaluated. The liquid depth inside the damper was considered to be 42 mm, which is equivalent to mass percentage of 1%. Damping of structural models can be changed using an efficient semi-active control algorithm, which acts by changing the angles of baffles. The investigation of the numerical results shows that the rotation of the baffles during the excitation improves seismic behavior of the structural models and reduces the roof displacement. The results show that higher reduction is observed under the near-field earthquakes than the case under far-field earthquakes. However, this reduction is lower for the baffle angles of 50 and 70 degrees due to the curving of the streamlines inside the damper and increase of the damping coefficient in these angles.