Vibration Analysis of Large Silos: Modeling and Experiments

During the discharge of large cylindrical silos, significant vibrations, pulsations and quaking are often created. The vibrations are typically accompanied by acoustical emissions referred to as silo honking. Such noise pollution is a health and safety concern for workers at site (e.g., hearing loss due to prolonged exposure). From a structural integrity standpoint, the vibrations contribute to the fatigue failure of the load carrying members and connections and endanger the safety and integrity of the overall system. The associated forces and deflections are often further amplified due to resonance between the silo support structure and the discharge loading frequencies. In order to avoid exciting one of the silo support structure modes, researchers and engineers often employ simplified mass-spring models to predict the natural frequencies of the structure. However, these models do not always capture all of the important modes of the silo system. In this paper, a detailed finite element model is developed to predict all of the dominant modes (vertical and side-way swaying) of the system. Beam, shell, and solid elements are used to model the silo support structure, silo walls, and the potash mass, respectively. For the experimental study, several strain gauges and accelerometers were installed on a full-scale silo support structure to determine the frequency of loading during material discharge. This paper summarizes the results of the numerical and experimental study that has been performed.