Evaluating the vertical stiffener effects on the dynamic behavior of a cylindrical intake tower under pulse loading

In this study, the effects of vertical stiffeners on the behavior of a cylindrical intake tower were investigated. For this purpose, four vertical stiffeners with variations in height levels ranging from 0 to 100 m were utilized. The conditions of the surrounding reservoir and water inside the intake tower were considered in five scenarios: (I) Without a surrounding reservoir, (II) With a half-full reservoir and empty interior, (III) With a half-full reservoir and half-filled interior, (IV) With a full reservoir and empty interior, and (V) With a full reservoir and fully-filled interior. Abaqus software was utilized for modeling purposes. A total of 55 models were constructed, each subjected to four types of pulse loading with different frequencies, resulting in a total of 220 analyses. The results indicate a rising trend in the first natural frequency of the structure with increasing stiffener height up to 50 m, followed by a descending trend with further increments in height. The results demonstrated that for low-frequency loadings, the presence of vertical stiffeners at lower height levels can reduce the maximum displacement. Additionally, for low-frequency loadings, stiffeners can decrease the structural damping time. The values of the first and third principal stresses within the body of the intake tower significantly increase in the presence of stiffeners, particularly at their locations. Considering the continuity of the intake tower and stiffeners, although the presence of these stiffeners may reduce the maximum horizontal displacement and the first principal stresses in the cylindrical section of the tower in some cases, overall, it leads to an increase in the principal stress values throughout the entire body of the tower and at the locations of the stiffeners. This phenomenon ultimately decreases the safety of the tower.