PSI - Issue 62

Andrea Maffei et al. / Procedia Structural Integrity 62 (2024) 1006–1013 Andrea Maffei et al. Structural Integrity Procedia 00 (2019) 000 – 000

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corrosion. The fibers, on the other hand, have high tensile strength and are the main provider of the strength of fiber reinforced composite. GFRP bars are produced through a molding process. For this reason, they can’t be bent on the construction site like steel but require off-site prefabrication. Despite this, GFRP bars are particularly suitable in the context of curb design because it requires regularly shaped and repetitive stirrups. The use of GFRP rebars as replacement of steel rebars, has several advantages: • increased durability of reinforced concrete; the absence of corrosion issues can considerably reduce maintenance costs; • simplified construction site operation due to the low specific weight of glass fiber bars (approximately one fourth of that of steel); • simplified drilling operations for fasteners installation, due to the lower shear strength of GFRP compared to steel stirrups. This work shows an example of GFRP supplementary reinforcement design, considering class H4 barriers for bridges commonly present on the Italian national system of motorways. The design of the curb supplementary reinforcement (stirrups) is carried out by considering the impact load transmitted by a vehicle in the event of a collision, according to the Italian construction code (NTC18). Verifications of the curb-barrier connection system are conducted in accordance with EN 1992-4:2018 while the mechanical properties of the GFRP reinforcements are assumed according to CNR-DT 203/2006 technical recommendations. Finally, an economic comparison is provided between two curbs of the same geometry, one reinforced with classic steel bars, the other with GFRP bars. The comparison is carried out in terms of the overall cost of the reinforcement per meter of length of the curb. 2. Design regulations, advantages and disadvantages 2.1. Regulatory framework Several international guidelines are currently available supporting the design, construction and control of fiber reinforced polymer composites. The use of GFRP in Italy is currently regulated by: • CNR- DT 203/2006 “Guide for the Design and construction of Concrete Structure Reinforced with Fiber Reinforced Polymer Bars” - June 2007; • “ Guideline for the identification, qualification and acceptance of FRP (fiber reinforced polymer) bars for structural use" of the C.S.L.P. (Higher council of the Public Works) - December 2021. The first one is an advisory document for the design, construction and control of concrete structures reinforced with FRP bars. The second one defines the technical specifications of the products that can be accepted on the construction site. Verifications of the curb-barrier connection system are conducted according to EN 1992-4:2018 “ Design of fastenings for use in concrete”. This European Standard provides a design method for fastenings which are used to transmit actions to the concrete, based on physical models consistent with EN 1990:2002. According to EN 1992-4 §7.2.1.2, when the concrete cone and edge failure are not verified, the use of steel reinforcement of the concrete support is allowed. Although GFRP rebars are not mentioned in this code, the use of GFRP as curb stirrups is physically possible. Even though the material exhibits brittle behavior, the verifications required by EN1992-4 for reinforcement bars (§7.2.1.9.1 and §7.2.1.9.2) are conducted within the elastic range and require values of strength and bond with concrete that are compatible with GFRP bars. Further to the previous point, the CNR-DT 203/2006 foreword reads as follows about the use of GFRP “ From a theoretical perspective, there are no conceptual differences in relation to the classical theory of steel reinforced concrete elements. That does need to be taken into account, is the different mechanical behavior of FRP materials, whose constitutive law is fundamentally linear elastic up to failure ”.