Vibration control of structures against near-field earthquakes by using a novel hydro-pneumatic semi-active resettable device

Near-field earthquakes, characterized by long-period velocity pulses with large peak ground velocities and accelerations, have led to severe damage to many civil structures designed in accordance with the current seismic codes. A novel hydro-pneumatic semi-active resettable device (HSRD) is proposed for vibration suppression of building structures subjected to near-field earthquakes. The main portion of this device is a cylinder-piston assemblage comprising four separate chambers filled with two different materials, that is, magneto-rheological (MR) fluid and pressurized air. The two sides of a bypass pipe are connected to the two adjacent MR fluid chambers in the middle of the cylinder, forming a closed-circulating loop. The bypass pipe has an on–off valve controlling the stiffness by adjusting its on–off threshold and a functional valve controlling the damping by changing the MR fluid's property. The initial stiffness of HSRD is set by adjusting the pressures or lengths of the two gas chambers. Simulation studies with a five-story and a 10-story building structures subjected to three near-field earthquakes are conducted to evaluate the performance of HSRD. Three semi-active control schemes are considered to create optimal hysteresis loops of HSRD for achieving prominent vibration mitigation. It is revealed that the device with all the control schemes is effective in vibration suppression of the structures suffering from near-field earthquakes, and the resetting control strategy has the best performance among them. The results validate the capability of HSRD assisted by a semi-active control strategy for vibration mitigation of buildings subjected to near-field earthquakes.