INTRODUCTION
GENERAL
Earthquake is an uncontrollable natural phenomenon that can damage even
the most well designed structure. The common perception for resisting a
seismic force is by strengthening the structure. The traditional
engineering design strategy for seismic protection is based on
increasing the design capacity and stiffness to accommodate foreseeable
lateral forces. It may not be the most efficient solution. The problem
of the conventional approach is that all seismic forces from the
foundation will be absorbed by the superstructure. Moreover, to make
sure that the capacity exceeds the seismic demand for a concrete
structure, a large amount of concrete and reinforcement is needed, which
in turn increases the cost of construction. The seismic base isolation
technique is precisely the opposite approach to the conventional design
strategy. It is not possible to control the earthquake itself but it is
possible to modify the demand that it creates on the structure by
preventing the seismic motions being transmitted from the foundation
into the structure above. It reduces the demand to make sure that it is
less than the capacity. Seismic base isolation is a part of a
structure’s seismic protection systems that reduces the effect of ground
shaking on the superstructure. It is a design technique that uncouples a
structure from its base or ground and thereby protecting it from
damaging effects of ground motion[1]. The concept of base isolation
is that the structure is separated from the ground during an earthquake,
the ground will be moving but the structure will be dormant. It actively
damps the seismic energy thereby preventing the seismic energy to be
transferred to the superstructure and damage it. This ingenious strategy
not only meets all serviceability and functional requirements but also
reduces the requirement of concrete and reinforcement needed to increase
the capacity of structure to resist being damaged by ground motion.
Thus, construction cost is reduced.
The concept of seismic base isolation is more than a century old[1].
However, not until the 1970’s it evolved into the practical strategy for
seismic-resistant design. Modern concept of shock absorbing by base
isolation with a bi-linear force-displacement characteristic was
inspired from the shock-absorbing soft first story concept developed by
Mark Fintel and Fazlur R. Khan, 1969[2]. In 1976, the Earthquake
Engineering Research Centre (EERC), now known as the Pacific Engineering
Research Centre (PEER), of the University of California at Berkeley, was
the first institution in the United States to conduct a study on the
feasibility of using raw rubber bearings as base isolators to defend
buildings from earthquakes[3]. Among all types of base isolation
system actually the rubber bearings are the most effective isolators as
they are comparatively effortless to manufacture, can survive for a long
time, do not require external restoring force and are outstandingly
resistant to ecological degradation.
BACKGROUND
MOTIVATION
LIMITATION
PRESENT CONDITION IN BANGLADESH
SCOPE AND OBJECTIVES
The motivation behind this dissertation paper is twofold. First, it is
meant to provide a concise point of departure for researchers and
practitioners alike wishing to assess the current state of the art in
the control of civil engineering structures. Second, and perhaps more
important, it provides a link between structural control and other
fields of control theory, pointing out both differences and similarities
and where future research and application efforts are likely to prove
fruitful.
The paper is organized in the following way: section 2 deals with
passive energy dissipation; section 3 deals with active control; section
4 deals with hybrid and semi-active control systems; section 5 discusses
sensors for structural control; section 6 deals with smart material
systems; section 7 deals with health monitoring and damage detection;
and section 8 deals with research needs. An extensive list of references
is provided in the references section.
Given the very broad and interdisciplinary nature of the field of
structural control and monitoring of civil infrastructure systems, it is
not feasible to discuss or cite all relevant publications and
applications. The writers have done their best to present a balanced
view of the developments in the field of structural control and
monitoring, however, only a limited number of references could be cited.
Consequently, absence of a citation of a particular work should not be
construed as implying anything about the publication’s merit. Where
appropriate, publications in technical journals were preferred for
inclusion over related publications in proceedings. Also, when
discussing control theory, emphasis was placed on those issues related
to the physical behavior of civil structures as opposed to sophisticated
developments in control system theory.
Chapter 2