Demountable joints between tubular members (RHS/SHS) using self-drilling screws (SDS) can be attractive for simple lightweight steel construction, yet their structural response is difficult to predict with conventional design approaches. This is because load transfer is governed by local screw shear, bearing, and contact nonlinearity. Therefore, the component “SDS in shear” had not been characterized yet in terms of initial stiffness to provide reliable values to be applied in a simplified mechanical model. This work proposes simplified, simulation-informed models that enable efficient prediction of stiffness and resistance for hollow-section joints assembled with SDS. The strategy combines detailed finite element (FE) calibration at the fastener level with reduced-order representation at the joint level. First, a local 3D FE model of a single SDS in single-shear is calibrated to reproduce the experimental force–slip response obtained from medium-thickness steel sheets [1]. The calibration focuses on an effective representation of the screw–sheet interaction through contact/interface stiffness and material nonlinearity, providing a robust “SDS shear component” law suitable for reuse. Next, the calibrated component is upscaled to multi-screw layouts and embedded into global models of tubular beam-to-column joints via equivalent connector elements (springs) placed at screw centers. This hybrid modelling approach retains the correct load path and redistribution between screws while avoiding explicit modelling of threads and fine contact in the full joint. Validation against laboratory tests on representative partially sleeved tubular joints [2] shows that the reduced model captures the global moment–rotation response and the governing failure mechanism with enough engineering accuracy, while reducing computational cost by orders of magnitude compared to fully detailed models. The resulting framework supports rapid parametric studies (screw diameter, spacing, sleeve length, wall thickness) and provides a clear route to component-based design rules for semi-rigid hollow-section joints assembled with SDS. REFERENCES [1] A. García, C. López-Colina, M.A. Serrano y M. Colino, Self-drilling screws under shear joining medium thickness steel sheets, COMPLAS 2025. [2] A. Garcia, C. Lopez-Colina, M.A. Serrano, I. Garcia, L.R.O. De Lima and F.L. Gayarre, “Characterization of semi-rigid RHS T-joints with self-drilling screws”, Thin-Walled Structures, 213, 113350 (2025).