Analytical model for load-deformation relationship of interior slab-column connections subjected to unbalanced moment

Damage in flat-plate floor systems subjected to lateral loading is known to concentrate at interior slab–column connections, yet practical nonlinear modeling approaches for performance-based seismic design remain limited. In the present study, an analytical model is presented for nonlinear static analysis of flat-plate floor systems under lateral loading. Slabs and columns are represented by elastic plate and line elements, while slab–column connection zones are idealized using pseudo-rigid spandrel/beam elements connected to columns through integrated nonlinear hinges. The integrated hinges combine flexural, shear, and torsional components, modeled with moment–rotation relationships formulated from KDS 14 provisions and calibrated using finite-element simulations. The approach is validated against a calibrated finite-element model and experimental data from the literature. For the 18 local-hinge comparisons, the model-to-FE ratio of peak unbalanced-moment resistance has a mean of 0.83 and a CoV of 4.4%, corresponding to a systematic average underprediction of approximately 17% that is inherited from the KDS 14 strength formulation. A parametric study is then used to derive simplified hinge moment–rotation relationships suitable for practical performance-based design.