Seismic Design of Spherical Pressure Vessels

Spherical pressure vessels are globally used for storage of pressurized liquids or gases of different hazard classes. An adequate seismic design of these structures must consider their particular structural behaviour and consequences of possible damage or failure. A study of the current standard situation for seismic design of pressure vessels revealed significant gaps and missing design rules, in particular for spherical pressure vessels. Within the European Research Project INDUSE the seismic performance and applicability of existing European and American codes to pressure vessels with cylindrical and spherical shape were investigated. This paper describes the results of a study on different examples of spherical pressure vessels which were selected to be representative for the current practice. The study comprised numerical investigations as well as simplified models for the estimation of the dynamic properties of the vessel structures. It is shown, which failure modes and stress concentrations areas are crucial in the event of an earthquake. In addition engineering calculation methods to determine fundamental periods and internal forces for braced and non-braced spherical pressure vessels were developed and compared to results of numerical simulations. The applicability of behaviour factors is discussed based on proposals made by European and American codes in comparison to own results. Recommendations for the behaviour factor of spherical pressure vessels with different dimensions were developed based on push over analyses and non-linear incremental dynamic analyses. Furthermore the influence of sloshing effects in spherical vessels, for which no specific rules are given in the codes, was investigated according to the current state of the art.