Vibration Characteristics of Buildings in Addis Ababa

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Addis Ababa University


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.



Vibration Characteristics, Buildings in Addis Ababa