Numerical modelling of the seismic behaviour of steel silos and tanks

Structural and seismic engineering are involved in the design of new industrial facilities and in the upgrading of existing plants. Silos and tanks are relevant components of lifelines and industrial facilities, where they are used for storing a huge range of different solids and liquids. Silos and tanks are special structure, which are sensitive to quite high failure rate. They should be design to resist to several loading conditions, which strongly depend both from geometrical features and storage material. Now to date, design procedures are based more on experience than scientific knowledge and more detailed acquaintances about structural behaviour are required in order to improve the design rules. This study is finalised to reach a better understanding of seismic response of elevated silos and tanks. In order to achieve this aim, Incremental Dynamic Analysis (IDA) methodology has been employed. Moreover an assessment of several behaviour models is pursued. In particular, different kinds of Finite Element Models (FEM) have been performed, by using the commercial code Straus7. Initially, an elevated silo filled with like-granular material, is taken into account. Its supporting structure is on one side framed while on the other one is braced; furthermore two different braced systems have been considered. Then, an evaluation of different kind of response has been possible if ground acceleration is applied in two separate directions. A complete FE model provided of bricks elements and a simpler FE model with distributed masses on the silo walls have been compared. Their results are commented and confronted with particular attention about failure modes, localization of weakness and collapse behaviour. In the second part, possible models to describe seismic behaviour of tanks are presented. As first step, a study about the capacity of finite elements to correctly describe fluid dynamic is developed. Outcomes are compared with theoretical solution and with results obtained by using simpler approximate models. Finally, on the base of previous considerations, an elevated tank FE model has been implemented too. In particular, the opening structure has been filled by fluid of the some weight of the granular material. In this way, direct observation of effects due to liquid presence, such as sloshing, has been possible. Also in this case, considerations about employing of complete FE models or approximate models have been presented.