A smart mechatronic base isolation system using earthquake early warning

Earthquake is one of the most devastating natural disasters. In the last few decades, many seismic mitigation techniques have been developed. They include passive, semi-active and active control which have been proven their effectiveness in events of earthquakes. Among them, base isolation has been regarded as a mature technology and commercialisation is common in earthquake-prone countries. This technology decouples the main structure from its foundation and effectively lengthens the natural period of vibration, away from resonance vibration. However, the lateral stiffness of base isolation devices is generally too low to resist serviceability lateral forces such as wind and flood which may cause unacceptable lateral movements of the structure. Added lateral stiffness and/or damping is usually required. On the other hand, the Earthquake Early Warning (EEW) system which uses different arrival time of seismic P and S waves is readily available in Japan, Taiwan, parts of China and Europe. This technology offers more possibilities for improvement of earthquake mitigation technique.

This project develops a smart mechatronic base isolation system which can be triggered by the EEW system. It uses the earthquake early warning signals and nearby monitoring signals to determine the situation and automatically switches to the appropriate anti-seismic mode. In the first phase of research, a one-dimensional system is developed and tested on an electrical shake table. A prototype smart mechatronic base isolation system is developed. In this prototype design, electromagnetic shear keys which lock the base isolator are released either by simulated EEW signals or on-site accelerometers. The advantage of this design gives the main structure a very strong stiffness under in-service condition (i.e. when there is no ground motion) while maximizing the effectiveness of base isolation when ground motion is anticipated. The system is fully automated, and the main structure is re-entered once ground motion ceases. In the second stage, a two-dimensional base isolation, created by low-friction linear bearings is developed and activation of base isolation is carried out by linear actuators. In the third stage, the system is developed further. Light Detection and Ranging (LIDAR) sensors are added to monitor position of base isolator in real-time, an active control strategy is added into the microcontroller and actuation is carried out by stepper motors. Using the feedbacks provided by the sensor the active base-isolation system re-position the main structure in real-time. The research presented in this thesis opens up new opportunities in future seismic risk mitigation of civil structures. By connecting the EEWS and mechatronic devices, the performance of traditional base isolation system can be enhanced.