This paper deals with experimental modal analysis of bolted storage tank, commonly used in many applications such as sewage treatment. Experimental modal analysis is crucial for the evaluation of dynamic properties, which helps with the assessment of wind-induced loads. Vortex shedding at specific wind speeds can excite natural frequencies, potentially causing damaging vibrations. Although the tanks have a simple cylindrical shape, their construction from overlapping steel sheets, stiffening girders, and bolted joints complicates numerical modelling. This makes it difficult to accurately define stiffness, mass distribution, damping, and boundary conditions. To minimize these differences, a prototype of a small, bolted tank is designed and built including all above-mentioned parts. Experimental modal analysis is performed on the prototype using three configurations of upper girders. The first case is without girders, the second one uses standard L-shaped beams, and the third one uses a new designed wind girder. It was found that the lowest first natural frequency f = 42.3 Hz was for the case with new designed wind girder. The first natural frequency of the tank without girders was f = 50.1 Hz. The most suitable case was a tank equipped with L-shaped girder with the first natural frequency equal to f = 86.7 Hz.
Science Journal 