PSI - Issue 84

S. Lorefice et al. / Procedia Structural Integrity 84 (2026) 669 – 676

672

1.0 m below ground level, neglecting the stiffness contribution of the surrounding soil.

Fig. 4. 3D View of the FEM models: (a) three-span bridge (b) six-span bridge

The structural behaviour was described using the Total Strain Crack (TSC) constitutive model. In addition to the standard mechanical parameters (Young’s modulus, Poisson’s ratio, and density), the model is uniquely defined by the compressive and tensile strengths, the corresponding fracture energies, the characteristic finite element length, and a correction factor accounting for shear behaviour. For both masonry and concrete, a linear softening law was adopted in tension, while a parabolic constitutive law was assumed in compression; shear behaviour was modelled using a linear law with constant inclination. 5.2 New steel deck The replacement of the existing steel structure was deemed necessary due to its advanced state of deterioration, characterized by widespread corrosion over all exposed surfaces, local thickness losses, impact damage, and plate buckling phenomena, resulting in a significant reduction of the current structural safety level. Moreover, the structure was found to be inadequate to withstand the static and seismic actions prescribed by current technical standards and by the RFI Design Manual (MdP-RFI), which are more demanding than those considered in the original design. The new steel structure consists of a truss girder with an upper-track configuration with a theoretical span of approximately 54.36 m and a spacing between the main girders of 4.50 m. The truss configuration derives from the discretization of the upper chord into 12 panels, resulting in individual panel lengths of 4.53 m. The structure is equipped with lateral walkways at different elevations to allow periodic inspections, ensuring both structural safety and regular railway operation. The track alignment includes a horizontal curve with a constant radius of approximately 443.55m, associated with a cant resulting in a vertical difference of about 12 cm between the inner and outer rails. Overall, the structure is composed of welded built-up steel sections and standard rolled profiles, appropriately arranged and differentiated according to the distribution of design internal forces. Several bracing systems are provided, including top, bottom, and transverse bracings. The proposed bearing system consists of PTFE sliding bearings, in compliance with the MdP-RFI provisions. In order to avoid the development of tensile forces in the bearings, the longitudinal geometry of the structure was tapered near the support regions, reducing the girder spacing from 6.50 m at midspan to 4.00 m at the supports.

Fig. 5. Geometric layout of the steel structure

The implemented numerical model is based on a simplified idealization of the real structure and consists of a one dimensional beam model, whose geometric dimensions, cross-sections, materials, and boundary conditions are