A team of researchers from the University of Lisbon has recently published a study in Engineering, presenting a reliability-based code calibration procedure for pultruded glass fibre-reinforced polymer (pGFRP) I-section beams under specific loading conditions. The study aims to determine optimal partial safety factors for design rules, focusing on web-crippling phenomena under end-two-flange (ETF) and interior-two-flange (ITF) loading cases with unfastened flanges.
Pultruded glass fiber-reinforced polymer (pGFRP) profiles are gaining popularity in civil engineering due to their high strength-to-weight ratio, durability, and resistance to harsh environmental conditions. However, their use has been limited by issues such as high deformability, buckling sensitivity, and a lack of reliable design codes. The study addresses a significant gap in the current design guidelines, particularly the absence of design rules for web-crippling failures under ETF and ITF loading conditions in the European standard CEN/TS 19101.
The researchers conducted a comprehensive review of existing literature on web-crippling of pGFRP beams and presented a detailed description of a resistance model based on the direct strength method (DSM). This model accounts for the three main failure modes typically triggered by web-crippling loading scenarios: web crushing, web buckling, and the interaction between web crushing and web buckling.
The reliability-based code calibration procedure adopted in the study follows the “seven-step approach” proposed by the Joint Committee on Structural Safety (JCSS). This approach involves defining the scope of the code, setting code objectives, choosing the code format, and establishing probabilistic models for material properties, loads, geometrical dimensions, and resistance model uncertainty. The study considers four distinct materials with varying coefficients of variation (CoV) for key material properties such as compressive strength and elastic modulus.
The results of the calibration procedure indicate that the variability of material properties significantly influences the reliability indices and partial safety factors. The study found that the most relevant material property for defining the partial safety factor is the transverse compressive strength (𝑓_𝑦,c) for web crushing and the transverse elastic compressive modulus (𝐸_𝑦,c) for web buckling and web crushing-web buckling interaction failures. The optimal partial safety factors (𝛾_Rd) were determined for different materials and loading conditions, with higher values obtained for materials with lower variability.
The study concludes that different 𝛾_Rd values should be adopted for ETF and ITF loading cases to ensure structural safety. For simplification, conservative 𝛾_Rd values of 1.30 (ITF) or 1.50 (ETF) are proposed for web-crippling loading cases when considering the Lind’s penalty function. Lower 𝛾_Rd values can be obtained if the least square function is used.
This research contributes to the development of reliable design rules for pGFRP I-beams susceptible to web-crippling, providing a systematic approach to balance safety and cost-effectiveness. Future work will involve extending this methodology to other cross-section shapes and incorporating alternative resistance models based on numerical approaches.

The paper “Reliability-Based Code Calibration of Pultruded Glass Fiber-Reinforced Polymer I-Section Beams Under End-Two-Flange and Interior-Two-Flange Web-Crippling Loading Cases,” is authored by André Dias Martins, Ângelo Palos Teixeira, Nuno Silvestre, João Ramôa Correia. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.03.019. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.