Experimental and analytical evaluation of the dynamic characteristics of conical shells

Truncated conical shaped shell structures are used in various engineering applications such as components of missiles and spacecrafts and liquid containers for elevated water tanks. The purpose of this study is to evaluate the dynamic characteristics of such type of shell structures when subjected to a transverse dynamic excitation. This paper focuses on conical steel vessels as superstructure of elevated tanks. However, results of the study can be applied to other conical shell applications. The study is conducted experimentally using a shake table device and numerically using an in-house developed shell element model. In the experimental phase, the fundamental frequency and the corresponding mode shape of a small-scale aluminum conical shell model were evaluated. Results of this experiment were used to validate the numerical model by comparing the measured values to those predicted by the model. The analytical study was then extended to evaluate the dynamic characteristics of conical steel tanks covering a wide range of practical dimensions. The study included the case of open and fixed-roof tanks. The performed analyses led to the development of a number of charts that can be used to identify the natural frequency, the mode shapes and the generalized mass and stiffness of conical tanks for both the fundamental and the cos(θ)-modes of vibration. These results would be very useful in assessing the dynamic response of conical tanks when subjected to wind and earthquake loads.