PSI - Issue 62

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

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GFRP bars are not covered by a harmonized standard. For this reason, according to NTC18 §11.1, the manufacturer has two options: • request the “ European technical assessment ” (ETA) for the construction product; • request a "Technical Assessment Certificate" (CVT) according to the “G uideline 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 CVT of the construction product must contain the following characteristics: • production process; • nominal size and bar shape (straight or shaped); • fibers and matrix nature; • fiber volume fraction; • physical, geometrical and mechanical characteristics. 2.2. Advantages The use of GFRP rebars as replacement of steel rebars in concrete curb design has several advantages. • High ultimate tensile strength, typically between 800 and 1000 MPa, depending on the diameter of the bar. This value is almost double the steel yielding strength and would theoretically lead to a lower reinforcement requirement. However, some partial factors reduce the design strength to about 35% of the ultimate tensile strength, as will be explained in the next section. • GFRP bars are not susceptible to corrosion which makes them suitable for structures, like bridge curbs, exposed to harsh environmental conditions (e.g. chloride corrosion favored by the use of deicing salts). For this reason, the concrete cover can be reduced since there is no need to protect rebars against corrosion. • Barrier installation usually requires post-installed fasteners. This operation can be particularly onerous in closely spaced steel stirrups. GFRP bars have lower shear strength than steel, so they offer lower resistance during the drilling operation required by post-installed fastening systems. • GFRP bars weigh about a quarter of what steel weighs. This aspect can speed up rebar installation and improve workplace safety reducing the injury risk associated with lifting and positioning the reinforcement cages.

2.3. Disadvantages Replacing steel reinforcement with GFRP reinforcement involves some disadvantages.

• Brittle behavior of the material compared to traditional steel reinforcement. Experimental tests on GFRP bars have shown that the failure of the specimen does not occur in a localized point but in a widespread mode. The fibers inside the polymer matrix collapse at different times and in different areas, generating a substantially ductile failure (Figure 1a). This aspect is not considered in CNR-DT 203/2006 where GFRP constitutive law is fundamentally linear elastic up to failure. For this reason, the partial factor for ultimate limit states is equal to 1.5 compared to the 1.15 usually adopted for steel.

Fig. 1. Comparison between failure of (a) GFRP bar and (b) a steel bar.