PSI - Issue 78

Annalisa Franco et al. / Procedia Structural Integrity 78 (2026) 1245–1252

1247

μ X

mean value of the variable X

σ

shape parameter of the fitting distribution tensile strength of dry fabric tensile strength of IMC system standard deviation of the variable X threshold of the fitting distribution

σ f σ u σ X

ϑ

Φ

cumulative probability function of the standard normal distribution

2. Definition of partial safety factors for design The calibration of partial safety factor for material strengths is based on the principles of the First Order Reliability Method (FORM)(EN 1990, 2023). According to section 8.3.5 of EN 1990, the design value of resistance R d for a specific design situation shall be calculated from the equation:

  

  

1

1

X





; ; R R X a F  d d d

; ; k

R

a F 



 

Ed

d

Ed







Rd (1) where Rd is a partial factor associated with the uncertainty of the resistance model, and for geometric deviations, if these are not modelled explicitly; R denotes the output of the resistance model; is a conversion factor accounting for scale effects, effects of moisture and temperature, effects of ageing of materials, and any other relevant parameters; k represents the characteristic values of material or product properties; m is a partial factor for a material property accounting for unfavourable deviation of the material or product properties from their characteristic values, and the random part of the conversion factor ; d denotes the design values of geometrical property; F Ed denotes design values of actions. For simplicity, as indicated in EN 1990, clause 8.3.5.1, the partial factors Rd and m given in Eq. (1) may be combined into a single partial factor for material property: M Rd m      (2) 2.1. Partial safety factor for material m According to clause 8.3.6 of EN 1990 (EN 1990, 2023), the design value of a product property is expressed as: (3) With the meaning of symbols already introduced in clause 2. By neglecting the conversion factor (i.e., ൌͳ ), since the tests were carried out under standard environmental conditions, the partial factor for the material properties m can be simply obtained by: (4) Therefore, to have a sound basis for the material partial factor m , a statistical analysis of experimental data under standard environmental conditions is therefore necessary to individuate the best fitting distribution to be used for the assessment of characteristic and design values of the investigated generic product property. The following procedure will be therefore presented, already introduced and applied by the authors in the calibrations of partial safety factor for organic matrix composite materials (Franco et al., 2025; Occhiuzzi et al., 2020; Salzano et al., 2019): Rd m k d m X X    k m   d X X