PSI - Issue 64

Francesco Bencardino et al. / Procedia Structural Integrity 64 (2024) 932–943 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Conclusions The paper showed a real case study concerning the strengthening of damaged RC frames using C-FRP laminates. The RC structure was made up of nine identical portal frames, which seven of them exhibited cracks likely due to exceeding the maximum allowable live load level. At the time of the intervention, due to the lack of specific guidelines about the use of C-FRP systems for structural applications, it was necessary to design the strengthening of the RC frames based on experimental data. From the experimental results, it was first observed that there were significant advantages in terms of load capacity for the beam strengthened with a C-FRP plate (positioned on the tension surface) compared to the RC control beam. However, the former beam (A1.1) exhibited a brittle failure resulting in a significant loss of ductility compared to conventional RC specimens. This aspect was mitigated by using external anchorage devices which increase the exploitation ratio of the C-FRP plate and thus its effectiveness. Based on the experimental results, the rehabilitation intervention was designed following the configuration used for beam A1.2, which included both the use of a C-FRP plate and the use of external steel end anchorages. For comparative purposes, the design of the same intervention using the procedure outlined in the current available CNR DT 200 R1/2013 Italian Guideline was also evaluated. The results showed that the theoretical approach provides significantly more conservative results compared to those obtained using experimental data, with values of ε fd,exp / ε fd ranging from ~2.55 (for beam A1.1) to ~3.45 (beam A1.2). However, despite the conservative approach provided by the CNR-DT 200 R1/2013, the design flexural strength of the strengthened beam in the section where the crack occurred increased by approximately 34% compared to the unreinforced case. By using more representative design strain values, the design flexural strength can be further increased. Consequently, this approach also allows higher load levels to be considered that the structure can withstand at the design stage compared to the currently proposed theoretical value. Today, nearly 30 years after the intervention, the structure is in excellent condition, demonstrating the good durability properties of the C-FRP system used and the effectiveness of the design procedures adopted. This highlights the importance of conducting experimental studies for design purposes and of continuously improving normative formulas in order to achieve greater accuracy. Acknowledgements The activities developed in this scientific work were carried out during the PhD course XXXVII cycle (R. Curto), PON 2014-2020, and the University of Cala bria, Azione IV.5 “Green”. Partial f inancial support from the Italian Department of Civil Protection (Project: DPC/ReLUIS 2022-2024) is also gratefully acknowledged. References Bank, L.C. 2006. Composites for Construction : Structural Design with FRP Materials . Hoboken, New Jersey: John Wiley & Sons. Bencardino, F., Colotti, V., Spadea, G., Swamy, R.N. 2005. “Shear Behavior of Reinforced Concrete Beams Strengthened in Flexure with Bonded Carbon Fibre Reinforced Polymers Laminates.” Canadian Journal of Civil Engineering 32(5): 812 – 24. CEN. 2002. EN 1991-1-1:Eurocode 1: Actions on structures - Part 1-1: General actions - Densities, self-weight, imposed loads for buildings. European Committee for Standardisation, Brussels. CEN. 2004. EN 1992-1-1: Eurocode 2: Design of concrete structures -Part 1-1: General rules and rules for buildings. European Committee for Standardisation, Brussels. CEN. 2005. EN 1998-3: Eurocode 8: Design of structures for earthquake resistance -Part 3: Assessment and retrofitting of buildings. European Committee for Standardisation, Brussels. Correia, J. R. 2015. “Fibre - Reinforced (FRP) Composites.” In Materials for Construction and Civil Engineering: Science, Processing, and Design , Dordrecht: Springer Netherlands, 501 – 43. CND-DT 200 R1/2013. 2014 . Guide for the design and construction of externally bonded FRP systems for strengthening existing structures - Materials, RC and PC structures, masonry structures . National Research Council, Advisory Committee on Technical Recommendations for Construction, October 10 th 2013 - release of May 15 th 2014, Roma, Italy. ACI 440.2R-17. 2017. Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures . American Concrete Institute, ACI Committee 440. Farmington Hills, MI.