Vibration Characteristics of Buildings in Addis Ababa
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Date
1999-06
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Addis Ababa University
Abstract
Dynamic loading acting on structural systems may result from
several sources such as wind and vehicular motions, etc. The
type of dynamic input, which is of greatest importance to the
structural engineer undoubtedly is the one that is induced by
earthquakes.
Buildings constructed in Seismic Zones are subjected to
earthquake ground motion in addition to other types of loads. If
one tries to generate response spectrum curves of a structure for
different recorded ground motions, large variations will be
obseIVed in both the response spectral values and the shape of
the spectrum curves. These variations depend on many factors,
such as magnitude, source, and variation in geological formation
along the path, local site condition and the nature of the building.
The recent trend of increasing height and scale of building
structures accelerated the research and investigation activities in
the area of Earthquake Engineering, with the aim to get rational
and safe earthquake resistant design criteria. Consequently, one
n
of the current problems in evaluating earthquake response of a
building is how 1D find out period of vibration of a building.
Recent developments in the techniques for measuring period of
vibration of building have permitted us 1D obtain important
experimental information reganling the dynamic behavior of a
building during earthquakes.
The fundamental period of buildings can be obtained by one of
the following methods: -
1) Microtremor measurements: here ambient building
vibrations are measured by using microtremors.
These ambient VIbrations called microtremors operate
at a very low strain level. Properly interpreted,
microtremors give the fundamental period of vibration
of the building.
2) Code Method -or-Equivalent Static Analysis: this gives
an approximate formula that can be used to determine
the first mode period of a building.
3) Dynamic Analysis: is a sophisticated level of analysis
available for finding period of vibration of buildings,
that employs Dynamic Time-History Analysis or
Response Spectral Analysis.
III
The comparison of experimental results with the results obtained
by empirical formulas and dynaJnic analysis will facilitate the
engineers' understanding of the an a lysis and design of building
structures subject to dyn amic loading.
In the "Introduction", the background and the purpose of this
study are described. In the second chapter Period of vibration of
selected buildings are determined by u s ing Microtremor. In the
third chapter Period of vibration of buildings a re determined by
using the Code Method. In the fourth ch apter periods of
buildings are determined by using Dynamic Analysis. In the fifth
chapter Comparison of results obtained by Microtremor, CodeMethod
and Dynamic Analysis are done. In the last chapter,
Conclusion was made ba sed on the results obtained.
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Keywords
Vibration Characteristics, Buildings in Addis Ababa