Assessment of Earthquake Analysis Methods of Intake Towers
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Date
2011-10
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Addis Ababa University
Abstract
Seismic analysis of an intake tower may be carried out using one or more methods from the
methods Seismic Coefficient (SCM), Equivalent Lateral Force (ELFM), Response Spectrum
(RSM) and Modal-Time history (MTHM) Methods. SCM, ELFM or RSM may produce response
quantities with magnitudes bigger or smaller than those of refined method (MTHM). How big or
small are the magnitudes in comparison with those of the refined method? In other words, are the
magnitudes of SCM, ELFM or RSM overestimated or underestimated when contrasted with those of
the refined method (MTHM)? Answering these questions through detail investigation is the core
objective of this study.
In order to meet the core objective, an investigation of the seismic analysis methods of intake
towers was conducted. The investigation was conducted by performing elastic seismic analysis of a
squat free-standing intake tower, using the conventional and refined methods; and comparing the
results of the analysis.
The investigation started by selecting a suitable intake tower and its location for the study. In this
regard, the squat free standing intake tower in kesem Dam irrigation project, in Afar Regional State,
was found to be suitable. The project is located in East African Rift Valley which is largely prone to
earthquake excitations.
After selecting the intake tower and its location, the next step was structural, material and
hydrodynamic modeling. Following the modeling, in put ground motions in form of response spectra
and ground acceleration time-histories were developed. Next, seismic analysis of the intake tower
was carried out using the models and the input ground motions; and applying each of the methods
at a time. Finally, the results of the analysis were examined.
From the examination, the study concluded that the magnitude of response quantities computed
with SCM, ELFM or RSM were significantly different from those of the refined method. Moreover,
the study concluded that the magnitudes of the response quantities computed with three methods
were underestimated. So, SCM, ELFM or RSM, especially SCM, are inappropriate for detail seismic
analysis of squat free-standing intake towers.
As result, the study decided that MTHM shall be used for final and detail elastic seismic analysis of
free-standing squat intake towers. However, further investigation are required in order to extend
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the conclusion to other classes of intake tower such as free-standing slender intake towers and
inclined intake towers. Similarly, other investigations are desirable in order to extend the
conclusions of this study to inelastic analysis methods of intake tower.
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Structures