Influence of roof on dynamic characteristics of dome roof tanks partially filled with liquid

The influence of roof on the natural frequencies and the modes of fixed roof, ground supported, liquid storage tanks is presented in this paper. Attention is given to partially filled tanks with the same heights of 12.19 m and the aspect ratios (H/R) of 2, 1.52, and 1.33. The bottom of tanks is considered to be anchored to the foundation. The effect of the roof, along with the liquid height, on dynamic properties is investigated. For this purpose, each tank is modeled in 4 liquid levels, equal to 1.80, 4.80, 8.50, and 10.90 m and in two various roof conditions: with roof (WR) and open top (OT). The finite element package ANSYS is used to model the tank–liquid systems. Tank roof and wall are meshed by shell elements and the liquid is modeled using fluid finite elements. The fluid–structure interaction is taken into account by coupling the nodes at the interface of the fluid and the shell in the radial direction. Results of ambient vibration tests are used to verify the numerical procedure in which good agreement is observed between the numerical and the experimental modal parameters. It is found that the influence of roof on natural frequencies of axial and vertical modes is negligible whereas its effect on the natural frequencies of circumferential modes is significant. It is also concluded that at low liquid levels, equal to 1.80 and 4.80 m, the tank roof does affect the axial modes of the tallest and medium height tanks while, at all of the considered liquid heights and aspect ratios, the tank roof affects the circumferential mode shapes; this confirms the idea that the roof does restrain the tank top against radial deformations.