Title of proposed paper for ASRANet International Colloquium 2002:

Probabilistic Treatment Of Uncertainties In Seismic Analysis Of Steel Tanks

Authors

G. Fabbrocino, I. Iervolino, G. Manfredi

Abstract:

Every structure, due to materials production and fabrication procedures since the construction is characterized by many random variables. On the other hand, actions due to seismic loads are random in their own nature. Current design procedures take into account this randomness providing partial safety factors about materials and considering design earthquake related to their return probability. This semi-probabilistic approach condensate a full stochastic analysis that consider contemporary randomness of input data and concur to obtain the design target failure probability.

For existing structures designed referring to former seismic guidelines, failures due to unsatisfactory structural performances can produce catastrophic consequences, thus assessment of structural vulnerability can be carried out using a full probabilistic analysis that is a powerful method, and provides user friendly tools as the fragility curves.

Large atmospheric steel tanks for oil storage used in industrial and power facilities match all problems discussed, but are characterized by firm international design standards and construction repetivity, in fact their dynamic behaviour can be characterized, in a simplified way, only by height/radius ratio.

Evaluation of failure probability related to given limit state functions is a complex task for structural engineers; it is dependent upon performances of materials, structural resistant mechanisms, constraints and also external actions, but opens new scenarios to evaluation of safety level for plants exposed to relevant risk.

Results of reliability analysis in terms of comparison of structural “demand” and “capacity” treated as lognormal independent random variables are discussed; it is a first approach to the development of fragility curves or annual failure probability (total risk). Procedure starts from dynamic analysis based on easy to manage deterministic structural model, i.e. a two degrees of freedom model taking into account content sloshing and sliding of unanchored tanks, and is based on a appropriate stochastic calculation on limit state functions.

Contact:

Department of Structural Analysis and Design

University of Naples Federico II

Via Claudio 21 - 80125 Naples, Italy

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