PSI - Issue 62

Nico Di Stefano et al. / Procedia Structural Integrity 62 (2024) 809–814 Nico Di Stefano, Anna Bontempi, Paolo Pizzini, Fausto Minelli / Structural Integrity Procedia 00 (2019) 000 – 000

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Before the tests a preliminary diagnostic phase was necessary to design the test set-up, then, after the tests, an extensive diagnostic has been developed only for beam N2. In fact, for beam N1, the test was stopped for the testing of a future strengthening technique. Diagnostic involved the identification of rebars position, extraction of both longitudinal reinforcement and stirrups; for the concrete, it was not possible to properly extract specimens and the compressive strength was evaluated through Windsor tests. The results of the invasive diagnostic on N2 rebars are shown in Table 1 in terms of mean rate of mass loss, mean yield and ultimate stress, elongation at failure and modulus of elasticity. Concerning the rebars, results underline something which is well known in literature: stirrups corrosion is much more severe than the one in longitudinal rebars, because of their external position as with respect to the section and because of the lower diameters (Cairns et al. 2005).

Table 1: tests results of the in-deep diagnostic of N2 rebars.

M corr [%]

f ym [MPa]

f um [MPa]

ε Agt [%]

E s [Gpa]

1° longitudinal layer 2° longitudinal layer

22%

3,8%

287

412

203

2,8%

325

469

18%

206

Stirrups

34,7%

268

344

6%

185

The tests were conducted under 4 points loading and in displacement control, with an electromechanical jack of about 1500 kN capacity. The set-up is shown in Figure 3a. Shear span over effective depth ratio (a/d) was chosen to be near 2.5 value, which is recognized as the most critical condition for shear.

(a)

(b)

Figure 3: (a) tests set up; (b) instrumentation used for beam N1.

Several instruments were placed to measure displacements, deformations and crack widths in different positions of the specimens. As an example, in Figure 3b the instrumentation employed for beam N1 is shown. As underlined before, specimen N1 was not tested up to failure, but, as we can see in Figure 4a, the test stopped when a clear flexural behaviour was shown; in N2 test the rupture occurred (Figure 4b) always in bending showing the concrete crushing of the upper flange after yielding (Figure 5).