Influence of the roof on the natural periods of empty steel tanks

The influence of a fixed roof on the natural periods of vibrations of thin-walled aboveground steel tanks with clamped boundary conditions at the base is studied. Tanks with open-top, self-supported roofs, and roofs supported by rafters are considered, along with different tank aspect ratios. The self-supported roof geometries considered include dome, cone, shallow cone, and flat roofs; whereas the rafters supported roofs geometries study cone, shallow cone, and flat roofs. The effect of the aspect ratio, along with the roof configuration on the natural periods is discussed. It was found that the vibration of empty tanks with a fixed roof is dictated either by cylinder modes or roof modes of vibrations. For self-supported roofs predominant roof modes resulted, whereas for tanks with roofs supported by rafters, cylinder modes dominate the dynamic behavior of the tank. Roof dominant modes had natural periods that remain constant regardless of the aspect ratio considered. Cylinder modes, on the other hand, were characterized by natural periods that showed a linear dependence with the aspect ratio of the tank.