Mechanism-Based and Experimentally Calibrated Modelling Strategy for Prestressed I-Shaped UHPFRC–Steel Composite Beams with Continuous Shear Connectors

This paper presents a finite element investigation of prestressed I-shaped Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC)–steel composite beams with continuous puzzle-shaped shear connectors. Experimentally derived material and bond relationships are implemented in three-dimensional models in ATENA Science. The tensile response is identified from flexural tests evaluated by digital image correlation and specimen-level inverse analysis, while the compression input is derived from cube, cylinder and prism tests. Beam I-2 is used for structural model selection. Separate studies assess the tensile reference-size sensitivity at a fixed mesh and the mesh sensitivity at a fixed reference size. The selected 35 mm mesh and 25 mm Tension Characteristic Size are subsequently transferred to I-1 and I-3 without further specimen-specific adjustment. For I-1 to I-3, peak-load deviations are +10.1%, +4.9% and +0.7%, respectively; the corresponding deflection deviations are +8.3%, +1.0% and −12.7%. The models reproduce strand-controlled ultimate failure and qualitatively reproduce the observed steel-web strain-localisation patterns. An additional I-4 analysis reaches strand rupture instead of the experimentally observed tensile-flange splitting and overestimates its peak load by 25.4%, demonstrating a boundary of validity of the adopted symmetry-constrained model. Internal tensile splitting demand, compressive inelasticity and transverse flange deformation are interpreted numerically within these limitations.