THE EFFECT OF VERTICAL COMPONENT OF BASE EXCITATION ON NON-LINEAR DYNAMIC BEHAVIOR OF CONCRETE COOLING TOWERS

Reinforced concrete cooling towers of hyperbolic shell configuration find widespread application in utilities engaged in the production of electric power plant. In designing critical civil infrastructure of this type, it is imperative to consider possible loading conditions that the cooling tower may experience. One important loading condition in different codes is earthquake excitation, whose influence on the integrity and stability of cooling towers is profound. Previous research has shown that the columns supporting a cooling tower are sensitive to earthquake forces, as they are heavily loaded Elements with low level of ductility, and understanding the behavior of columns under earthquake excitation is vital in structural design because they provide the load path for the self weight of the tower shell. For designing the concrete cooling towers, the horizontal component of earthquake acceleration is very important and usually the effect of vertical component of earthquake acceleration is ignored This paper presents the results of a finite element investigation of a representative “dry” cooling tower, using realistic horizontal and vertical acceleration data obtained from the recent and widely-reported Tabas, Naghan and Bam earthquakes in Iran. Three mentioned earthquakes applied to the structure, once with horizontal and vertical accelerations (HV state) and another without the presence of vertical acceleration (H state). The results of both analyses are reported in the paper, the locations of plastic hinges within the supporting columns are identified and the ramifications of the plastic hinges on the stability of the cooling tower are assessed. It is concluded that for the (typical) cooling tower configuration analyzed, the columns that are vital in providing a load path are influenced greatly by earthquake loading, and for the earthquake data used in this study the representative cooling tower would be rendered unstable and would collapse under the earthquake forces considered. So the research shows that the presence of vertical component of earthquake acceleration changes the response of structure, but the effect of that, is not comparable with the significant effect of horizontal component of ground acceleration.

کلیدواژه ها:

Concrete cooling towers ، Vertical component of earthquake acceleration ، Non-linear behavior ، stability