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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• The raw materials used in manufacturing GFRP, such as glass fibers and resins, are more expensive than steel. The manufacturing process involves specialized techniques that are more complex than manufacturing steel which can increase the overall cost. T he average cost of GFRP is about 6.5 €/kg for straight bars and 8 €/kg for shaped bars, much higher than steel, which costs less than 2 €/kg. The cost comparison between these two materials is not so simple because GFRP bars weigh about a quarter of what steel weighs. For this reason, a more in-depth analysis will be covered later in this paper. • Bending of fibers in GFRP causes a significant reduction (35% to 70%) in bend strength in comparison to the straight portion. The reason for this is the misalignment, or “kinking”, of fibers resulting from the molding process that are unable to fully contribute to load resistance. This involves a reduction of the capacity of the bent portion that depends on the manufacturing process and the ratio of the bend radius to the diameter of the bar. This aspect is considered through a partial factor  f,  that depends on the curvature radius of the shaped element. To limit the stress concentration at the bend, according CNR-DT 2003/2006, the radius of the bend shall not be greater than 6 diameters of the bar and the partial factor  f,  must be equal to 2. The use of lower values of the bend radius is allowed provided that the manufacturer performs experimental test to determine the characteristic strength of the bent portion. • As previously mentioned GFRP bars have lower shear strength than steel bars. This characteristic is an advantage during fasteners installation but at the same time damages GFRP stirrups. For this reason, in order to take into account the effective quantity of stirrups, it is necessary to reduce their span or increase their diameter. 3. Case Study 3.1. Geometry, material The curbs compared in this paper measured 0.70 m wide and 0.45 m high. The longitudinal reinforcement is realized in both cases by 12  16 bars. The transverse reinforcement is realized by  12/15 cm for steel and by  14/15 cm for GFRP. The geometry and the reinforcement details are shown in Figure 2.

Fig. 2. Geometry and reinforcement details (a) steel reinforcement (b) GFRP reinforcement.

The characteristic compressive strength of concrete is equal to 40 MPa and the yield strength of steel bars is equal to 450 MPa. The tensile strength of straight GFRP bars is equal to 800 MPa while the tensile bend strength of the GFRP bent bars is 280 MPa. GFRP also shows a higher value than steel of bond strength to concrete. In the accidental design situations, like impact load, the partial factors for actions for ultimate limit states are taken equal to 1.0.