PSI - Issue 78

Roberto Nascimbene et al. / Procedia Structural Integrity 78 (2026) 193–198

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3. Local Modeling of the Beam-to-Column Joint The local behavior of the beam-to-column joint was modeled using Midas FEA, employing solid elements using reduced integration (Nascimbene (2013)) to capture the nonlinear response of the concrete in both the beam and column, as well as the grouted connection layer and the cementitious injections within the column’s anchorage holes. The internal reinforcement bars were modeled using embedded elements, whereas the through-bars crossing the grout layer were represented by truss elements with calibrated mechanical properties to reflect their axial performance. To account for potential separation phenomena, interface elements, functionally similar to contact elements, were included in the model. These interfaces simulate debonding between the beam and the neoprene pad, as well as detachment between the beam and the underlying grout layer (see Figure 2). For the compressive behavior of concrete and grout, the Thorenfeldt constitutive model was adopted, while the tensile response was captured using an exponential softening law. The steel reinforcement was modeled with a multi linear stress-strain relationship, enabling a detailed representation of yielding and strain hardening effects.

Fig. 2. Local finite element model of the Beam-to-Column Joint and embedded elements defined for steel.

Several simulation scenarios were conducted by varying key parameters, including the tensile strength of the grout, which governs crack initiation at the beam-grout interface, and the mechanical behavior and bond conditions of the bars passing through this region. The resulting deformation patterns and stress distributions are shown in the following figures, with particular emphasis on interface separation between column and grout, and strut action developing between the beam and column via the corbel support (Figure 3).

Fig. 3. Detail of the deformed shape of the developed model, including the interface elements between beam and grout, beam and neoprene, and column and neoprene, as well as the embedded reinforcement and the through-bars across the joint, modeled using truss elements. Also shown is the distribution of vertical stresses in the joint region.