BASE-ISOLATION TECHNIQUES FOR REINFORCED CONCRETE STRUCTURE

Abstract

Seismic design concept of a structure is different in many ways because of the uncertainty of the earthquake loading
and its behavior. Therefore, a restricted damage is allowed without allowing the collapse of the structure when subjected to
the most severe earthquake likely at the site thus ensuring safety of lives and its utility. Accepting the probability of damage, on
the basis that it is less expensive to repair when hit by an earthquake rather than making the structure earthquake damage
proof. This concept results in a cost-effective design, which will be liable to earthquake damage but will not collapse in an
event of severe earthquake. These design standards are also based on considerations of allowable stresses, permissible
inelastic strain, desired factor of safety against collapse, acceptable damage etc. Careful design & construction detail can
vastly improve the presentation of structure. For very significant structures/projects such as nuclear power plants, high dams,
high rise buildings, and long span bridges, etc. & their high cost requires high degree of safety than the ordinary structures &
therefore needs special design criteria. The major developments in basics idea & principles of seismic design, development of
standardized shape of response spectra and its application, base-isolation techniques ,design for strength & ductility,
developments in 2D/3D mathematical models and their behavior, soil-structure interaction and dynamic analysis,
reinforcement detailing, integrity and continuity of structure, properties of material, Energy dissipating devices, Regular mass
and stiffness distribution, increasing the plastic deformation capacity.
This assessment is presenting the future trends in earthquake resist design features in RCC structure using base isolation
methods, devices and concept. Conservative earthquake-resistant structural systems are fixed-base systems that are ‘fixed’ to
the ground base. They originate their earthquake resistance from their capability to absorb seismic energy in specially
designed regions of the structures, such as in beams near beam-column joints of RC frames. However, in base-isolated
systems, the superstructure is isolated from the foundation by certain strategies, which reduce the ground motion transmitted
to the structure. These devices assistance decouple the superstructure from destructive earthquake parts and absorb seismic
energy by addition of significant damping. In evaluation to fixed-base systems, this technique considerably reduces the
structural response and damages to structural as well as non-structural components. An important number of base-isolation
strategies have been developed. Designing a base-isolated arrangement is still a difficult complex process, and its dynamic
response tends to be more complex than the fixed-base system. Presently, only certain types of structures are best suited for
base-isolation for earthquake resistance, although technology is gradually overcoming these limitations.