|
Non-Linear
Seismic Analyses of High Rise Reinforced Concrete Buildings
-- Chandrasekaran
Srinivasan, Luciano Nunziante, Varun Gupta and Federicoa Carranante
A
majority of the existing building stock envisaging more earthquakes
in future increases the concern for their structural safety
and their compliance with the current seismic codes. Recent
geodetic update of Indo-Australian plate clearly shows that
India is expected to face high frequency of great earthquakes
and low frequency of moderate earthquakes in the near future.
The latest approach to displacement-based seismic design of
structures emphasizes on careful estimation of non-linear
properties of constitutive materials of RC building frames
and the use of appropriate analysis tools in order to ensure
a safe design. Displacement-controlled pushover analysis is
widely accepted as one of the reasonably accurate tools for
performing non-linear static analysis of structures under
seismic loads. In this study, first a non-linear time history
analysis (THA) is carried out on building frames of different
plan configuration subjecting them to El Centro and Kobe earthquake
time histories. Subsequently, modal pushover analysis (MPA)
is carried out subjecting these building models to the target
displacement, which equals the maximum roof displacement obtained
from THA. Numerical studies conducted show a step-by-step
collapse mechanism of building frames under lateral loads
using MPA procedure, tracing the plastic hinges formed at
various acceptance levels, namely immediate Occupancy (IO),
life safety (LS) and collapse prevention (CP). The study can
be seen as an improved method of conventional pushover, as
it accounts for: (i) modal characteristics of the building
inviting participation of higher modes; and (ii) target displacement
corresponding to the maximum tip displacement of the building
when subjected to two referral earthquakes. The results obtained
by employing this modified MPA show a significant improvement
in the estimate of design base shear for a desired performance
level in comparison to the primary results obtained from THA,
while maintaining its simplicity.
©
2008 The Icfai University Press. All Rights Reserved.
Development
of Strut and Tie Models for Simply Supported Deep Beams Using
Stress Trajectories -- Praveen
Nagarajan and T M Madhavan Pillai
Concrete
structural members can be broadly divided into two regions,
namely B or Bernoulli regions, where the strain distributions
are linear, and D or Disturbed regions, where the strain distributions
are non-linear. Though B and D regions are equally important,
D regions are still being designed using the thumb rule or
empirical equations, while well-defined theories are available
for designing B regions. It has been recently realized that
the Strut and Tie method is an effective tool for the design
of both B and D regions. Since this method is a realistic
approach, it has found place in many codes such as Euro code,
American code, Canadian code, Australian code and New Zealand
code. This approach is not described in detail in the current
IS 456:2000 code of practice for plain and reinforced concrete.
In a deep beam, the distribution of strain across the depth
of the cross section will be non-linear, and hence, these
structural elements belong to D regions. The existing IS 456
codal provisions for the design of simply supported deep beams
are empirical in nature. In this paper, the development of
Strut and Tie models for simply supported deep beams are discussed
and for this purpose, design aids are also developed. The
use of the design aid is illustrated using an example, and
is compared with IS 456 codal recommendations.
©
2008 The Icfai University Press. All Rights Reserved.
Optimal
Design of Plane Truss Using Particle Swarm Algorithm
-- C R Suribabu
Several
algorithms have been developed and applied to sizing optimization
problems that involve finding optimal cross sections (or dimensions)
of the elements of a structural system whose topology and
shape are fixed. This paper proposes a Particle Swarm Optimization
(PSO) for optimal design of plane truss. PSO is a relatively
recent heuristic search method whose mechanism is inspired
by the swarming or collaborative behavior of biological populations.
The objective of this research is to minimize the size of
truss members such that truss can have minimum weight, while
fulfilling the stress and deflection criteria. The paper outlines
the fundamental mathematical background of the PSO method
and suggests a possible implementation strategy for optimal
truss designs.
©
2008 The Icfai University Press. All Rights Reserved.
Experimental
Study of the Behavior of Concrete One-Way Slabs Reinforced
with Glass Fiber Reinforced Polymer Reinforcement --
R Sivagamasundari and G Kumaran
This
study focuses mainly on the flexural behavior of one-way concrete
slabs reinforced with Glass Fiber Reinforced Polymer (GFRP)
reinforcements under static and repeated fatigue loading.
A total of 32 one-way slabs are cast and tested such that
16 slabs are subjected to static loading and 16 slabs are
subjected to constant amplitude repeated loading. Different
parameters like thickness of slabs, reinforcement ratios,
types of reinforcements and grades of concrete are considered.
Based on this study, static load carrying capacities and fatigue
performance of the conventional and GFRP reinforced concrete
one way slabs are then compared.
©
2008 The Icfai University Press. All Rights Reserved.
Response
of Plate on Elastic Foundation Under Harmonic Moving Load
-- P
R Maiti, Rohit Saha and Sofia W Alisjahbana
The
vibration of plate rested on foundation to moving load is
a problem of great importance in structural dynamics. This
paper investigates the dynamic analysis of a finite plate
resting on an elastic foundation subjected to traversing point
load of harmonic nature, assuming the velocity of load to
be constant. The foundation has been modeled as Winkler foundation.
Formulations are developed in the transformed field domain
using: (1) a double Fourier transform in space; and (2) Laplace
Carson integral transform in time domain for steady state
response to harmonic moving load. The effect of the speed
of the moving load, the foundation stiffness and the dynamic
amplification factor are evaluated. The paper also investigates
the effect of load frequency on the deflected shapes, and
the maximum displacement.
©
2008 The Icfai University Press. All Rights Reserved.
Static
and Dynamic Analysis of Cylindrical Shells Using Integral
Equation Method -- P A Krishnan
and Simi Gopalan
The
present paper describes a detailed analysis of thin cylindrical
shells for static and free vibrations using an integral equation
method. The components are subjected to dynamic vibrations
which may hamper their proper functioning. Hence the vibration
studies play an important role. Integral equation method is
a matrix-oriented numerical method. Here, the shell is approximated
as a grid work of beams parallel to the edges. The highest
derivative is taken as an unknown and the panel is divided
into meshes by considering lines parallel to the edges of
the shell. The displacements are expressed in terms of these
unknowns at the discrete points in the mesh using Green's
functions and numerical integration using Simpson's rule.
The differential equations are converted into algebraic equations
which are solved for the unknowns. It is observed that good
results with less number of mesh points are obtained using
integral equation method. Also it is seen that the method
can be easily programmed. Parametric study has also been conducted
for different vertex angles and mesh sizes. Also results are
compared with solutions obtained using SAP.
©
2008 The Icfai University Press. All Rights Reserved.
|
July
'08