INFLUENCE OF PARTIAL SAFETY FACTORS ON DESIGN RELIABILITY OF STEEL STRUCTURES ‐ PROBABILITY AND FUZZY PROBABILITY ASSESSMENTS

The paper is aimed at the analysis of the influence of partial safety factors on the reliability of designing steel members. The reliability assessment of a steel member is based on extensive experimental research on real material and geometric characteristics evaluated by samples obtained from frequently manufactured products. Material and geometric characteristics are random variables represented by histograms during the probabilistic assessment of reliability. The random variability of structural dimensions and of material characteristics does not present the only source of uncertainty present during design according to standards. The reliability of steel structures design is also dependent on the partial safety factor values, which are specified by the design standards. Partial safety factors are basic indicators, which determine structural dimensions in relation to loading. The probabilistic assessment of reliability is performed as a parametric study in the first part of the numerical analysis. The probability of failure is analysed in dependence on values of partial safety factors of material, permanent loading and long time variable loading. Partial safety factors are considered as fuzzy numbers with triangular membership functions in the second part of the numerical analysis. Membership functions of failure probability are evaluated using the general extension principle. The most important results are then summarised and additional applications of the verifications of limit states design criteria are described.