Earthquake events are major threat to buildings and infrastructure that lead to casualties and economic loss. In India, government and public agencies have already started embracing advanced retrofit options to safeguard critical facilities against earthquakes. Seismic isolation is being used for civil engineering facilities (e.g., Bhuj hospital in Gujarat, Shimla Walker hospital, Patna Police Bhawan) outlining the growing interest in India for use of these systems. However, some unique challenges need to be addressed prior to the application of seismic isolation to critical structures. The internal non-structural components of critical structures (e.g., hospitals, emergency response centers) are quite sensitive to the vertical seismic excitations. The conventional base-isolated systems are intended for horizontal isolation and do not reduce the vertical acceleration characterized by high-frequency components. The previous attempts to develope three-dimensional isolation systems for buildings were ineffective due to lack of stability, performance and reliability issues, proprietary nature of devices, need of power supplies, and difficulty in the application at the actual site.

Recently an emerging branch of solid-state physics has inspired the researchers due to the development of phononic crystals which show frequency bandgaps for elastic waves. This innovating idea of manipulating phononic crystals for attenuation of elastic waves was then utilized on macro-scale for the construction of periodic foundations. The metamaterial-based periodic foundations were experimentally tested by many researchers both at large scale and at lab scale for attenuation of seismic waves. The seismic metamaterials were found to be effective in attenuating both vertical as well as horizontal vibrations. However, designing of metamaterial-based foundation for simultaneous reduction of vertical and horizontal vibration would be challenging. Hence, a three-dimensional isolation system that can efficiently mitigate the damaging effects of earthquakes by combining traditional isolation system with metamaterial based-isolated systems is proposed to developed and its feasibility would be investigated.

Many public buildings such as schools, hospitals, etc., where partial infill walls are present in reinforced concrete (RC) structures, have undergone undesirable damage/failure attributed to captive column effect during a moderate to severe earthquake shaking. Often, the situation gets worsened when these RC frames are non-ductile in nature, thus reducing the deformable capability of the frame. Also, in many parts of the Indian subcontinent, it is mandatory to use fly-ash bricks for construction so as to reduce the burden on the disposal of fly-ash produced at thermal power plants. In some scenario, when the non-ductile RC frame, partially infilled by fly-ash bricks, suffers major structural damage, the challenge remains on how to retrofit and restore it. Thus, in this study, two full-scale one-bay, one-story non-ductile RC frame models, namely, bare frame and RC partially infilled frame with fly-ash bricks in 50% of its opening area are considered. In the previous experiments, these models were subjected to slow-cyclic displacement-controlled loading to replicate damage due to a moderate earthquake. Now, in this study these damaged frames were retrofitted and an experimental investigation was performed on the retrofitted specimens to examine the effectiveness of the proposed retrofitting scheme. A hybrid retrofitting technique combining epoxy injection grouting with an innovative and easy-to-implement steel jacketing technique was proposed. This proposed retrofitting method has ensured proper confinement of damaged concrete. The retrofitted models were subjected to the same slow cyclic displacement-controlled loading which was used to damage the frames. The experimental study concluded that the hybrid retrofitting technique was quite effective in enhancing and regaining various seismic performance parameters such as, lateral strength and lateral stiffness of partially fly-ash brick infilled RC frame. Thus, the steel jacketing retrofitting scheme along with the epoxy injection grouting can be relied on for possible repair of the structural members which are damaged due to the captive column effect during the seismic shaking.