Local Shear Demand Correction Model for the Analysis of Infilled Frames Using Equivalent Struts

The paper presents a practice-oriented analytical formulation to evaluate the additional and total shear demand due to frame–infill interaction under seismic loads. The proposed methodology leverages the simple equivalent strut approach to model the infilled frame while estimating the actual shear demand with a straightforward analytical correction. The total shear demand is decomposed into the sum of the shear demand resulting from structural analysis and the additional demand due to the interaction with the infill. The formulation is based on the static equivalence between the equivalent strut macromodel and a refined-finite element micromodel of the infilled frame, which is assumed as the benchmark. A data set of experimental tests was defined and numerically replicated with the micro- and macromodels. The actual shear demand distribution is extracted from the refined micromodel using numerical integration at specific section cuts. A predictive analytical model for the additional shear demand was formulated and validated. Results show the enhanced capability of the proposed model, combined with the equivalent strut approach, to approximate the actual shear demand at the column ends compared with available models in the literature. The proposed approach enables step-by-step verification of the local shear demand during nonlinear analyses and predicts the maximum expected additional shear demand for design purposes.