Simplified methods for efficient seismic design and analysis of water-surrounded composite axisymmetric structures

Available simplified formulations for the seismic analysis of axisymmetric structures address materially homogeneous solids with uniform cross-sections, while generally neglecting the effects of higher vibration modes and soil flexibility. In this paper, we develop original simplified procedures that remove these restrictions for practical seismic design and safety evaluation of axisymmetric structures vibrating in contact with water. The procedures proposed take account of higher vibration modes, water compressibility and flexibility of underlying foundation of the structure. For practical purposes, the formulations are first derived while neglecting the effects of surface gravity waves, and are then extended to account for these effects when required. Composite axisymmetric structures made of different materials as well as those with non-uniform hollow cross-sections due to geometric irregularity of interior wall are covered. Step-by-step flowcharts are provided so that the calculations can be easily implemented in a daily practical engineering environment. Application of the proposed techniques is illustrated through the examples of homogeneous and composite axisymmetric tower-water systems with rigid and flexible foundations. The obtained results are successfully validated against advanced coupled fluid-structure finite element solutions.