Geology Reference
In-Depth Information
BASE ISOLATION SYSTEMS
to a level of around 10 isolated buildings per year
in 1990 and 1991(Naeim & Kelly, 1999).
There are many types of isolation systems used
today to protect the buildings from earthquakes.
Most of these systems incorporate either elasto-
meric bearings, with natural rubber or neoprene,
or sliding bearings, with the Teflon or Stainless
steel sliding surface. However, many new and
different isolation systems are proposed each
year, and the number of these systems continues
to increase year by year. This chapter discusses
only the elastomeric base isolators.
Base isolation technology is now well accepted
worldwide, and many example buildings are con-
structed in United States, Japan, New Zealand,
Italy, and China.
Seismic isolation systems represent another
form of passive control systems. In these systems,
a flexible isolation system is introduced between
the foundation and superstructure so as to increase
the natural period of the system. Since the period
of the base-isolated structures is long, in compari-
son with the fixed-base structures, therefore if the
earthquake motion at the site has a long period,
this can cause resonance phenomenon in the struc-
ture. In this situation, the isolation system may
have a reverse effect and increase the response of
the structure instead of reducing it. Examples of
this phenomenon have been reported at Mexico
City and Budapest. On the other hand, near fault
effects cause large velocity pulses close to the
fault rupture. Effects are greatest within 1 km
of the rupture but extent out to 10 km. The UBC
provisions require that near fault effects should
be included by increasing the seismic loads by
some factors. In time history dynamic analysis this
can be incorporated by including time histories
reflecting near fault effects. The near fault record
produces a much greater response than the far
fault record. The isolation system is being used in
near fault locations, but the cost is usually higher
and the evaluation more complex (Kelly, 2001).
The present investigation is a research study,
and its main objective is to simultaneously
In August 1909 J. A. Calantarients, a medical
doctor from northern English city of Scarborough,
wrote a letter to the Director of the Seismological
Service of Chile in Santiago to introduce him a
new method of building construction which now
is known as base isolation. The doctor proposed
that in seismically active countries, the buildings
can be built on “free joint” and a layer of fine
sand, mica, or talc that would allow the building
to slide in an earthquake. Dr. Calantarients had
mentioned in his letter that he had made experi-
ment with balls many years before it was done in
Japan (Naeim & Kelly, 1999).
John Milne, an Englishman who was living in
Tokyo in the years 1876-1895, built an example
of isolated building at the University of Tokyo.
This building was built on balls in Cast-iron plates
with Saucer-like edges on the heads of piles. In
1885 he explained his experiment in a report to
the British Association for the Advancement of
Science. Likely, he was the reference of the Japan
work, which Dr. Calantarients had mentioned in
his letter (Naeim & Kelly, 1999).
Application of the seismic base isolation
system has become a practical reality within the
last 30 years with development of multilayer
elastomeric bearings. Their development was an
extension of the use of elastomeric bridge bear-
ings and bearings for the vibration isolation of
buildings (Naeim & Kelly, 1999).
The first use of a rubber isolation system to
protect a structure from earthquakes was in 1969
from an elementary school in Skopje, Yugoslavia.
The first base-isolated building built in the United
States was the Foothill Communities Law and
Justice Center (FCLJC), a legal services center for
the County of San Bernardino, located in the city
of Rancho Cucamonga. The construction of this
building began in early 1984 and was completed
in mid-1985. In Japan the first large modern base-
isolated building was built in 1986, and increased
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