Seismic evaluation of the behavior of cylindrical intake tower under the effects of the far and near-field earthquakes by considering concrete rings and water-structure interaction

In this study, the effects of the concrete rings as well as the far and near field earthquake on the frequency and seismic behavior of the intake tower have been investigated. For modeling and analysis with considering the interaction of water and structure, ANSYS software which is based on the finite element method is used. For a better analysis of these models, two far and near field earthquakes have been selected and scaled to the same maximum value acceleration. To evaluate the effects of concrete rings on the behavior of the intake tower, 33 intake tower models have been modeled by considering concrete rings in different numbers and height levels. In the following, 66 analyzes have been performed for three modes of the tower, including only the structure of the intake tower without a reservoir, the intake tower with the surrounding reservoir and without inside water, and the intake tower with the surrounding reservoir and inside of the tower is full. The results of displacement, stress, and base reactions of the intake tower under the relevant analyzes have been compared with each other. Based on the results, it was found that the effects of a near-field earthquake at maximum displacements and stresses are far greater than a far-field earthquake. However, the values of the responses depend on the frequency of the earthquake in addition to its proximity to the field. The results also showed that surrounding water and internal water have different effects on the seismic response of intake towers affected by near and far-field earthquakes. The presence of water increases the effective duration of the earthquake on the response of the intake tower, especially in the near field earthquake. The results showed that by adding circular rings, the frequencies of the intake towers undergo significant changes, which require seismic analysis to evaluate its effects. In the case of an intake tower without a surrounding reservoir and an intake tower with a surrounding reservoir and without inside water, the maximum values of displacement decrease with increasing the height of the concrete rings and decreasing the distance between them. For an intake tower with a surrounding reservoir and full inside, in the case of far-field earthquake analysis, the greatest reduction in displacement occurs for an intake tower with a ring at 25 meters, while for a near field earthquake, in this case, the amount of displacement is further reduced with an increasing height level of concrete rings. The pattern of changes in the first principal stresses for all the studied models is also in accordance with the changes in the values of the maximum displacement. The maximum values of the base reaction for the intake tower without surrounding reservoir and the intake tower with the surrounding reservoir and without inside water for near field earthquake are greater than for the far-field earthquake while for the intake tower with surrounding reservoir and full inside for far-field earthquake it is more than a near field earthquake which is due to the frequency content of the desired earthquakes. Eventually, the results showed that adding concrete platforms at high and close to each other has very good and positive effects also reduces the maximum values of stress, base reaction, displacement, and relative displacement.