tesi A. Caggiano.pdf - EleA@UniSA - Università degli Studi di Salerno

1.3. Codes and Standards for Fiber-Reinforced Cementitious Compositesmaterials and fraction contents. Two residual values are typically taken as reference indesign: at first, it is considered the crack opening for Serviceability Limit State (SLS)verifications, then a second crack should be significant for the Ultimate Limit State(ULS) [Eurocode-2, 2004].The European standard EN-14651 [2005] proposes four different residual strengths: i.e.,f R1 , f R2 , f R3 and f R4 (Figure 1.11). They correspond to specific values of the C MOD j :C MOD 1 = 0.5mm, C MOD 2 = 1.5mm, C MOD 3 = 2.5mm and C MOD 4 = 3.5mm, respectively.Particularly, f R1 and f R3 are the FRC residual strengths representative forthe SLS and ULS, respectively.f Lσ N[MPa]f R1f R2f R3f R4CMOD 1 = 0.5 CMOD 2 = 1.5 CMOD 3 = 2.5 CMOD 4 = 3.5CMOD [mm]Figure 1.11: Typical curve of the nominal stress versus C MOD for FRC [EN-14651, 2005].Then, post-cracking residual strength and FRC toughness can be classified by usingtwo parameters: the first, which outlines the strength class, is given by f R1 , while thesecond parameter (identified with the letter "a", "b", "c", "d" or "e") recognizes theratio between f R3 and f R1 . Particularly, the strength classes, based on the characteristicvalue of f R1 (i.e., f R1,k ), are defined through the following values of f R3 /f R1 ratio: 1.0(if f R1,k ≥ 1.0 MPa), 1.5 (if f R1,k ≥ 1.5 MPa), 2.0 (if f R1,k ≥ 2.0 MPa), 2.5 (if f R1,k ≥2.5 MPa), 3.0 (if f R1,k ≥ 3.0 MPa), 4.0 (if f R1,k ≥ 4.0 MPa), 5.0 (if f R1,k ≥ 5.0 MPa), 6.0(if f R1,k ≥ 6.0 MPa), 7.0 (if f R1,k ≥ 7.0 MPa) and 8.0 (if f R1,k ≥ 8.0 MPa).The f R3,k /f R1,k ratio (being f Ri ,k characteristic values of f Ri ) can be represented withthe letters "a", "b", "c", "d" or "e", corresponding to the following characteristicstrength values:• "a" if 0.5 ≤ f R3,k /f R1,k ≤ 0.7;• "b" if 0.7 ≤ f R3,k /f R1,k ≤ 0.9;19