Constructing an Innovative Base-Isolation System under Masonry Structures

Seismic up-gradation of existing buildings is a very challenging task, as it requires us to consider historical and economical aspects of building. While proposing a seismic-retrofit scheme for a historical building, one should keep in mind that it should be compatible with existing materials, be least intrusive, monitorable and removable. A novel base-isolation technique has been proposed for the up-gradation of existing buildings against seismic actions which does not involve any alteration in existing buildings, and it is monitorable and removable. The method asks for the uncoupling of soil under, and around the building, with the help of closely spaced microtunnels, trenches and retaining walls. Closely spaced microtunnels will lay under the foundation of building, running parallel to one of the dimension of the building, and base-isolation devices will be fitted in lining of these microtunnels. These closely spaced micro-tunnels, along with the trenches and retaining walls around the building, will isolate the structure from seismic actions. This assembly of microtunnels, fitted with isolation devices, and trenches, around the building, will be able to filter seismic forces in both directions of building. The construction of these micro-tunnels, for realisation of innovative base-isolation technique, is the most critical phase, because it can have a detrimental effect on building. This work explores the potential applicability of the novel base-isolation method on masonry buildings by assessing susceptibility of masonry wall, having different physical and material characteristics, to damage (relating to aesthetic of building) inflicted by the construction of microtunnels in various soil conditions. The effect of transverse ground movements is considered in this study. A parametric study is conducted using 2-D (coupled) nonlinear finite element analyses, considering factors such as strength and stiffness of masonry, stiffness of soil, soil-structure interface, excavation sequence of tunnels, different physical characteristics of wall and depth of tunnels. The study shows the applicability of innovative base-isolation technique, highlights the vulnerability levels of walls of different physical characteristics, emphasizes the importance of excavation sequence of microtunnels in reducing risk of damage, and mentions symptoms that correlate with damage.