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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Based on the results in Table 1, the Ø20, Ø24 bars had an actual diameter consistent with the nominal one, whereas in four of the Ø 12 mm bars (transverse reinforcement/stirrups) the actual diameter measured was lower than the nominal diameter, which was indicative of an ongoing corrosion process. It was found that such four bars, characterized by mass losses in percentage ranging from 12.1% up to 42.1% (diameters from 9.13 mm to 11.25 mm), exhibited reduced values of yielding ( * y F ) and ultimate ( * u F ) loads compared to the counterparts detected in the uncorroded bars ( y F and u F , respectively), with decaying trends well fitted by a linear relationship with regression coefficient 0.012-0.014, as suggested by most literature studies (Di Sarno & Pugliese 2020), see Fig. 5. 4. Seismic vulnerability assessment of corroded bridge piers through nonlinear time-history analyses The seismic vulnerability assessment of the corroded bridge piers was performed through a simplified model of single pier, in compliance with the “Individual pier model” allowed by §4.2.2.6 of EC8-2 provisions (2005) and according to other literature studies (Tubaldi et al. 2021). The choice of this simplified model, at least for a preliminary analysis, is motivated by the rectilinear configuration of the bridge and by the relatively comparative height of the piers (apart from those near the abutments). The experimental tests were used to calibrate a numerical fiber-hinge model of the bridge pier, implemented in SAP2000 (CSi 2016).

Fig. 6. Fiber hinge model for nonlinear dynamic analyses on the single pier (individual pier model) under bidirectional seismic excitation.

The Section Designer built-in utility was adopted for modeling the cross-sectional characteristics of the piers (Fig. 6), by distinguishing confined and unconfined concrete, and by incorporating the corrosion-induced degradation laws for the steel bars located along the cortical part of the section (outer perimeter), according to two corrosion scenarios characterized by a uniform mass loss in percentage of 20% and 30% in line with the experimental findings (see Fig. 5), the latter being termed corroded scenario (1) and (2), respectively. The uncorroded scenario was also studied by adopting mean material strength parameters for concrete and steel bars, without any material degradation law. Nonlinearity was concentrated at the base section of the pier and ascribed to the flexural behavior only (Fiber P-M2-M3 hinge in SAP2000, CSi 2016), considering the slenderness of the piers and the remote probability of shear failure. Seven pairs of natural records were selected through the software REXEL v. 3.5 (Iervolino et al. 2010) and scaled to be spectrum-compatible with the elastic response spectrum of the installation site (latitude 38°.1095, longitude 14°.7222, return period 949 years corresponding to nominal life 50 years, importance class IV, reference life 100 years), as shown in Fig. 6. Based on geotechnical tests performed in