PSI - Issue 44

Ubaldo Saracco et al. / Procedia Structural Integrity 44 (2023) 721–728 Ubaldo Saracco et al./ Structural Integrity Procedia 00 (2022) 000–000

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participating mass and vibration period. These reduced differences denote that there are no substantial deviations of behaviour and, therefore, corrosion after 125 years does not affect particularly negatively the bridge vibration modes, despite the reduction of resistance of the corroded elements. Table 1. Degradation scenarios.

Vibration modes

Scenarios

X axis

Y axis

Z axis

M x [%]

T[s]

M y [%]

T[s]

M z [%]

T[s]

non corroded

89.33 88.80 85.11 88.98 88.85

0.136 0.135 0.144 0.137 0.136

77.44 77.21 77.50 77.31 77.26

0.895 0.902 0.929 0.898 0.892

80.95 80.90 80.84 80.99 80.82

0.694 0.719 0.719 0.697 0.692

1 2 3 4

Δ[%]

-5.66%

+5.56%

-0.30%

+0.78%

-0.14%

+3.48%

6. Conclusions In the current paper a 3D FEM model of the Pastorella bridge with some simplifications in comparison to the real structure was presented to perform push-down analysis under loads to evaluate its robustness. Information about materials’ mechanical properties and thickness reduction of corroded metal elements of the bridge were taken from literature sources. The structure is currently about 100 years old, but the corrosion forecast, to stay on the safe side, was calculated at t = 125 years to get information about the robustness behaviour also in the next 25 years. The most stringent formulation taken from literature provided a thickness reduction of the bridge structural components of about 1.30 mm. This thickness loss was applied to the entire examined sections as homogeneous corrosion. The corrosion damage was applied to five scenarios identified as follows: scenario 0: uncorroded bridge; scenario 1: corroded deck; scenario 2: corroded lower chord; scenario 3: corroded vertical braces and scenario 4: corroded vertical members. Subsequently, non-linear static analyses were carried out to evaluate the structure’s useful life. From analysis results it appeared that only scenario 1 with corroded deck elements and scenario 4 with corroded vertical members exhibit λ max > 1. To stay on the safe side, this load multiplier was measured before the first collapse phenomena although, following large displacements, hardening phenomena could be generated to increase the sustainable loading value. Moreover, scenarios 1 and 4 are those attaining the greatest displacement until collapse. Finally, linear dynamic analyses were conducted to identify vibration periods and masses excited by the seismic action, highlighting small differences of behaviour among the various scenarios. Finally, the performed analyses allowed to reach only a primitive knowledge of the bridge’s robustness and the related failure modes due to the inability of performing detailed inspections. For this reason, further developments of the study will foresee direct measurement of the thickness loss of structural elements due to corrosion to predict more effectively the robustness level of the Pastorella bridge. References Castaldo, P., Gino, D., Marano, G.C., & Mancini, G. (2022). Aleatory uncertainties with global resistance safety factors for non-linear analyses of slender reinforced concrete columns. Engineering Structure 255 . doi.org/10.1016/j.engstruct.2022.113920. Di Lorenzo, G., Formisano, A., Terracciano, G., & Landolfo, R. (2021). Iron alloys and structural steels from XIX century until today: Evolution of mechanical properties and proposal of a rapid identification method. Construction and building materials (302). Gino, D., Castaldo, P., Giordano, L., & Mancini, G. (2021). Model uncertainty in non-linear numerical analyses of slender reinforced concrete members . Structural Concrete 22 . doi.org/10.1002/suco.202000600. ISO9223. (2012). Corrosion of metals and alloys-Corrosivity of atmospheres-Classification, determination and estimation. ISO9224. (2012). Corrosion of metals and alloys-Corrosivity of atmospheres-Guiding values for the corrosivity categories. Kotes, P., Strieska, M., Brodnan, M., Odrobinak, J., & Gocal, J. (2018). Rapid tests of corrosion in corrosion chamber. Materials Science and Engineering . doi:10.1088/1757-899X/365/5/052013. Ministerial Decree 17/01/18 (NTC 2018). (2018). Technical codes for constructions. Rizzo, F. Di Lorenzo, G., Formisano, A., & Landolfo, R. (2019). Time-Dependent Corrosion Wastage Model for Wrought Iron Structures. American Society of Civil Engineers . doi:10.1061/(ASCE)MT.1943-5533.0002710. STACEC S.R.L. (2007). FaTa-Next . Available at https://www.stacec.com/ElencoDownload.aspx. Wikipedia. List of bridge failures . Available at https://en.wikipedia.org/wiki/List_of_bridge_failures. Accessed on 11/07/2022. Yamaguchi, K., Yoshida , Y., & Iseda, S. (2010). Analysis of influence of breaking members of steel through truss bridges. Stanford , CA, USA: Stanford University.