PSI - Issue 62

Francesco Bencardino et al. / Procedia Structural Integrity 62 (2024) 972–982 Bencardino/ Structural Integrity Procedia 00 (2019) 000 – 000

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A rectangular critical cross-section of 350mm×1300mm assuming the slab collaborate modestly in the bending and shear (and so negligible) was considered (results are on the safety side accordingly). The concrete cover was found equal to 30 mm. Regarding the steel reinforcement, a set of 6Φ32 and 2Φ32 were detected by pacometer for the bottom and upper bars, respectively. While, Φ8 with two arms each 200 mm spacing were for stirrups. The design values of the strengths were evaluated being 18.7 MPa and 273 MPa for the compression of the concrete and the tensile of the steel, respectively. The bending resistant moment was computed equal to 1590 kNm. Thus, it was greater than the acting bending moment on the two edge beams (safety check = satisfied with a safety factor capacity/demand = 1.17) and, at the same time, lower than the acting bending moment on the two central beams (safety check = not satisfied with a safety factor capacity/demand = 0.87). The shear capacity was governed by the crisis of the steel stirrups and calculated equal to 136 kN. Thus, the safety check was not satisfied in both the critical cross-sections of the beams with a safety factor capacity/demand equal to 0.35 and 0.22 for the edge and internal beams, respectively. 4. Strengthening intervention design Bending and shear reinforcement are essential components in the design of RC-beams, helping to ensure their structural integrity and ability to withstand applied loads. Longitudinal bending reinforcement is primarily used to resist the bending moments that occurs in a RC-beam under external loads. It consists of adding high-tensile resistant materials that are placed along the bottom of the beam, parallel to its length, in the tension zone. In this area, it enhances the beam ’ s ability to carry the applied loads without cracking or failing in tension. Shear reinforcement is used to resist the shear forces that occur in a concrete beam. Shear forces act parallel to the cross-section of the beam and can cause it to fail by sliding or shearing. Shear reinforcement typically takes the form of new stirrups-like material, which are U-shaped or bent steel bars that are placed vertically in the beam ’ s cross-section, surrounding the longitudinal bars. The retrofitting effectively “ tie ” the longitudinal bars together and help to prevent the concrete from cracking and spalling due to shear forces. They also redistribute the shear forces along the length of the beam. The spacing, size, and configuration of shear reinforcement, such as the number and geometry, are the parameters to be determined. Assessing these reinforcements with FRP offers several advantages, particularly in the context of concrete structures, among the others: • high strength-to-weight ratio . FRP materials are lightweight compared to steel, yet they offer excellent tensile strength. This lightweight property makes them easier to handle and transport and reduces the overall weight of the structure, which can be crucial in some applications. • Corrosion resistance . Unlike steel reinforcements, FRP materials are non-metallic and do not corrode. This is a significant advantage, especially in harsh environments where corrosion can weaken steel reinforcements over time. In marine or coastal areas, or in structures exposed to de-icing salts, FRP reinforcements can extend the lifespan of the structure. • Durability . FRP materials have excellent resistance to environmental factors such as chemicals, UV radiation using a suitable material cover, and freeze-thaw cycles. This durability ensures that FRP reinforcements maintain their strength and structural integrity over an extended period. • Ease of installation . FRP reinforcements can be fabricated into various shapes and sizes, making them adaptable to different structural configurations. They are often easier to install than traditional steel reinforcements because they don ’ t require complex welding or additional protective coatings. • Reduced maintenance . Due to their corrosion resistance and durability, structures reinforced with FRP materials typically require less maintenance over their lifespan, leading to cost savings in the long run. The sizing and verification calculations of the sections externally reinforced with the FRP-system were carried out according to CNR-DT 200/2004, the available guideline at the intervention time.