PSI - Issue 44

Dario De Domenico et al. / Procedia Structural Integrity 44 (2023) 633–640 Dario De Domenico et al. / Structural Integrity Procedia 00 (2022) 000–000

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minimizing the negative loglikelihood function. This probability distribution fitting leads to the determination of statistical parameters of the concrete compressive strength, namely the mean R cm = 30.41 MPa, the 5% fractile strength R ck ,5% = 22.25 MPa and the CoV = 18.1%.

Fig. 4. Lognormal distribution fitting of concrete compressive strengths from cores and SonReb tests of piers of the Zappulla viaduct.

Pachometer tests revealed that the spacing of the stirrups was larger (up to 38 cm) than that indicated in the design drawings (20 cm), with a mean value of 27 cm (CoV 17%): this is a crucial parameter for the seismic vulnerability assessment of RC piers, as it directly influences the confinement action induced by transverse reinforcement. The corrosion potential mapping, with respect to a saturated Cu/CuSO4 reference electrode, was performed to compute the oxidation level of wide surfaces of RC piers as per UNI 10174:1993 standards. Chromatic maps (as shown in Fig. 3) indicated the potential measured on the investigated area: for carbon steel bars, potential values lower than -350 mV are generally symptomatic of an ongoing corrosion process (Appendix X1 of ASTM C876-91). It was noted that some tests led to very low values of corrosion potential, especially those in which the corroded bars were evidently revealed by macroscopic observation. Finally, tensile tests were carried out on some portions of extracted steel bars, including different diameters and corrosion conditions (see Table 1).

Table 1. Experimental results from tensile tests on steel bars extracted from RC piers. Ø [mm] N. bars actual diameter [mm] mean (CoV) [MPa] mean (CoV) [MPa] mean (CoV) [ − ] mean (CoV) 20 3 20.1 (0.97%) 429.5 (3.42%) 667.1 (2.19%) 12.9 (4.26%) 24 8 24.0 (0.65%) 423.1 (2.74%) 678.3 (3.58%) 11.9 (9.35%) 12 6 12.1 (2.46%) 446.9 (7.13%) 671.4 (4.60%) 13.1 (6.46%) 12 * 4 10.2 (8.66%) 412.8 (5.59%) 630.0 (3.55%) 12.0 (13.69%) * Values calculated in corroded bars with reduced area compared to nominal diameter Ø 12 mm.

Fig. 5. Corrosion-induced degradation of yielding (left) and ultimate (right) loads of steel bars extracted from piers of the Zappulla viaduct.