Development of semi-active magnetorheological-integrated inerter systems for vibration control

Protecting civil structures against damage caused by wind disasters and earthquakes has perennially gained the interest of academic and engineering communities. Numerous studies have been conducted to mitigate the vibration within the buildings, which can be generally categorised into two methodologies: 1) damping method by absorbing energy from the primary systems, which is generally achieved by utilising dampers or energy harvesters; 2) detuning approach via suppressing the energy transferred from the vibration sources to the superstructure. It is worth noting that damping and detuning are concomitantly observed in practical scenarios, either by design or inadvertently. Of all potential detuning methods, reducing the natural frequency stands out as a straightforward and promising approach, which can be realised either by increasing the mass or diminishing their stiffness. The reduction of stiffness is proved to be effective, whereas inherently leads to pronounced deflections under large static loads. Similarly, augmenting the structural mass is constrained to be truly effective only when the added mass is commensurate with the original mass of the structure. This method incurs considerable costs and maintenance requirements. Fortunately, a two-terminal device named inerter has been proposed. The forces exerted by this device are proportional to the relative acceleration between its two terminals. This proportionality is defined by the term ‘inertance’, measured in kilograms, representing the apparent mass of the device. Through utilisation of transmission mechanisms, inerters can exhibit a large apparent mass using lightweight structures. Consequently, inerters can serve as a viable alternative to traditional mass in reducing the natural frequency of civil structures with reduced cost and feasible installation. Semi-active vibration control systems have been explored and developed in recent years to combine the benefits of both passive and active systems. These methods employ smart materials, such as magnetorheological (MR) materials, allowing for more efficient and responsive control of systems, striking a balance between adaptability and energy efficiency. While semi-active controllable stiffness and damping devices have been extensively studied, a majority of the inerters developed so far are inherently passive. To truly bridge the mechanical-electrical analogy, the concept of controllable inertance has gained attraction in academic research. This thesis has effectively advanced the practical implementation of semi-active inerters by integrating MR technology into various designs and has investigated their use in seismic protection for civil infrastructures.