Author Name:- Tia Toby
Department of Civil Engineering
Abstract:- The main objective of the study is to evaluate the response
reduction factor of RC frames. We know that the actual earthquake force is
considerably higher than what the structures are designed for. The structures
can't be designed for the actual value of earthquake intensity as the cost of
construction will be too high. The actual intensity of earthquake is reduced
by a factor called response reduction factor R. The value of R depends on
ductility factor, strength factor, structural redundancy and damping. The
concept of R factor is based on the observations that well detailed seismic
framing systems can sustain large inelastic deformation without collapse and
have excess of lateral strength over design strength. Here the nonlinear
static analysis is conducted on regular and irregular RC frames considering
OMRF and SMRF to calculate the response reduction factor and the codal
provisions for the same is critically evaluated.
Keywords: Response Reduction Factor, Ductility Factor,
Strength Factor, Nonlinear Analysis, Regular and Irregular Frames, OMRF, SMRF
I. Introduction
The devastating potential of an earthquake can have major
consequences on infrastructures and lifelines. In the past few years, the
earthquake engineering community has been reassessing its procedures, in the
wake of devastating earthquakes which have caused extensive damage, loss of
life and property. These procedures involve assessment of seismic force demands
on the structure and then developing design procedures for the structure to
withstand the applied actions Seismic design follows the same procedure, except
for the fact that inelastic deformations may be utilized to absorb certain
levels of energy leading to reduction in the forces for which structures are
designed. This leads to the creation of the Response Modification Factor (R
factor); the all-important parameter that accounts for over-strength, energy
absorption and dissipation as well as structural capacity to redistribute
forces from inelastic highly stressed regions to other less stressed locations
in the structure. This factor is unique and different for different type of
structures and materials used. The objective of this paper is to evaluate the
response reduction factor of a RC frame designed and
detailed as per Indian standards IS 456, IS 1893 and IS 13920.The codal provisions for the same will be
critically evaluated. Moreover parametric studies will be done on both regular
and irregular buildings and finally a comparison of R value between OMRF and
SMRF is also done.
II. Definition
of r factor and its components
During an earthquake, the structures may experience certain
inelasticity, the R factor defines the levels of inelasticity. The R factor is
allowed to reflect a structures capability of dissipating energy via inelastic
behavior. The statically determinate structures response to stress will be
linear until yielding takes place. But the behavioral change in structure from
elastic to inelastic occurs as the yielding prevails and linear elastic
structural analysis can no longer be applied. The seismic energy exerted by the
structure is too high which makes the cost of designing a structure based on
elastic spectrum too high. To reduce the seismic loads, IS 1893 introduces a
“response reduction factor” R. So in order to obtain the exact response, it is
recommended to perform Nonlinear analysis. In actual speaking R factor is a measure of over strength and
redundancy. It may be defined as a function of various parameters of the
structural system, such as strength, ductility, damping and redundancy.
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