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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The superstructure is formed by two box-shaped girders (U-shaped PC girders closed on the upper part by the overlying RC slab) mutually collaborating in the transverse direction through five PC transverse diaphragms per span, three of which along the span. The 17 piers of the viaduct have variable height (from 17 m to 47 m), and a hollow, two-cell, rectangular cross section with dimensions 7.00 x 4.80 m, reinforced with 272 longitudinal bars (Ø24 mm along the first 5 m of height, and Ø20 mm beyond this height), and Ø12 mm stirrups @ 20 cm, angular bars Ø12 mm @ 20 cm (placed in the corners of the section) and brackets Ø12 mm @ 40 cm spacing, as shown in Fig. 1. From the technical reports and original design drawings retrieved, the materials employed for the bridge piers are concrete type IV (cube characteristic strength ≥ 25 MPa) and high elastic limit steel (“acciaio ad alto limite elastico” in Italian) whose median yield strength is 500 MPa (Verderame et al. 2011). 3. Experimental campaign 3.1. Visual inspection and defect identification The quality control of the bridge piers was initially carried out via visual inspection for identifying possible damage spots, cracking signs and/or material degradation phenomena. The photographs reported in Fig. 2 highlight a state of chloride-induced corrosion and diffuse cracking phenomena in the concrete cover, evident rust localized in the longitudinal and transverse re-bars. The oxidation of steel bars was further accelerated by the carbonation of concrete cover over the years. It is worth noting that some local interventions with repairing mortar were executed some years ago, but they were clearly not effective enough because of insufficient grip arisen between the added restoration material and the underlying deteriorated layer.

Fig. 2. Corrosion state of bridge piers of the Zappulla multi-span viaduct detected from visual inspection.

3.2. Description and interpretation of the experimental tests performed in situ To improve the knowledge of mechanical characteristics of materials and to better assess the seismic vulnerability of the piers, an extensive experimental campaign was planned and executed in the Zappulla viaduct. The tests included (cf. Fig. 3): i ) 21 core tests, i.e., extraction of concrete cylinders, cut with height-to-diameter ratio equal to one, subsequent identification of the de-passivation front (carbonation tests), and concrete compressive strength determination in laboratory; ii ) 59 SonReb tests (sclerometric tests for the determination of the rebound index, combined with ultrasonic pulse velocity measurements), for obtaining a larger (than the 21 cores alone) set of data concerning the mechanical strength of concrete, which are useful to draw statistically meaningful parameters of the concrete compressive strength; iii ) 7 pachometer tests for steel bar identification and for detecting spacing of stirrups; iv ) corrosion potential mapping with respect to saturated Cu/CuSO4 reference electrode in 41 locations; v )