Calibration of wind action combination factors from experimental data

The semi-probabilistic method is currently worldwide used for the assessment of the structural reliability. In European Countries, both partial factors and combination factors recommended in EN1990 are often adopted. However, in the case of climatic actions, this choice can lead to overestimation (underestimation) of design values of the actions and a calibration at National level is required. Based on wind climate data available in the literature, an attempt is made to calibrate the combination factors for wind action combined with imposed loads for Italy. Two methods are considered: the classical simplified method based on the Ferry-Borges and Castanheta’s approach and the Turkstra’s rule, and a method based on the simulations of the combined load effects. First, the variation of combination factors over Italy is shown. Then, the influence of uncertainties and of the imposed load model is evaluated. Finally, the differences between the two methods are discussed and a comparison with current combination factors suggested by Eurocode is made. Overall, it is shown that: local combination factors change over Italy without correlation with geographic coordinates; the simplified method overestimates combination factors; current values suggested by Eurocode overestimates the combined load effects.