Assessment of Earthquake Analysis Method of Intake Tower

Guyya. Uma Devi, D. Rambabu


Seismic analysis of an intake tower may be carried out using one or more methods from themethods 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 seismicanalysis 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 extendthe 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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