Inorganic matrix composite (IMC) systems represent a sustainable solution for masonry strengthening, thanks to their compatibility with substrates, low costs and good performances in extreme conditions. Among them, FRM (Fabric Reinforced Matrix) systems employ dry fabric embedded in lime or cement-based mortars.

The design of this strengthening technique relies upon the definition of the design strength, which is obtained from the characteristic values through appropriate partial factors, which are commonly indicated in building codes or design guidelines [1]. Following the principle of ‘design-by-testing' pursued by EN 1990 [2], successfully employed by the authors for the calibration of partial factors for the strengthening technology using organic matrixes [3-5], the paper presents the results of a statistical analysis based on a large experimental activity for the qualification of several FRM systems by different manufacturers. Results of tensile tests under standard ambient conditions were used to calibrate the partial safety factors.

The paper will discuss the obtained results in comparison to the factors currently prescribed by design provisions, in particular giving an overview of the behaviour of various types of fibres and therefore focusing on some aspects which may be the subject of future revisions of design guidelines.

References

[1] CNR-DT 215 (2018), Guide for the Design and Construction of Externally Bonded Fibre Reinforced Inorganic Matrix Systems for Strengthening Existing Structures, National Research Council (CNR), Rome, Italy.

[2] EN 1990:2023. Eurocode - Basis of structural and geotechnical design: European Committee for Standardization (CEN), Brussels, Belgium.

[3] Occhiuzzi, A., Ceroni, F., Franco, A., Salzano, P., & Bonati, A. (2020). Experimental results of a national technical assessment procedure on commercial FRP for structural strengthening: wet-lay-up systems. Materials and Structures/Materiaux et Constructions, 53(1). doi: 10.1617/s11527-020-1439-5

[4] Salzano, P., Bonati, A., Ceroni, F., Crisci, G., Franco, A., & Occhiuzzi, A. (2019, 24-26 June 2019). Statistical analysis on mechanical properties of FRP materials for structural strengthening. Paper presented at the 7th ECCOMAS, COMPDYN, Crete, Greece.

[5] Franco, A., Bonati, A., Ceroni, F., & Occhiuzzi, A. (2025). Partial factors and environmental conversion factors of various externally bonded FRP systems: code requirements vs experimental results. Paper presented at the 12th International Conference on Fiber-Reinforced Polymer (FRP) Composites in Civil Engineering, CICE 2025 Lisbon, Portugal.