Supplemental Materials

A large number of parametric calculation results of internal force, yield rotation and ultimate failure rotation for specimens with narrow, medium and wide beam flanges under eight working conditions are summarized in Tables S1–S3. These detailed data are not fully displayed in the main text to avoid redundant content and disrupt the logical flow of core conclusions. Table S1 records the anti-progressive collapse indicators of narrow-flange substructures, including the maximum axial force of left and right beams, peak positive/negative bending moments at four key sections, joint yield rotation and corrected ultimate rotation. Table S2 and Table S3 list the corresponding mechanical response data for medium-flange and wide-flange specimens, respectively. All tables cover the parametric series of varying beam depths, spans, left-right beam stiffness asymmetry ratios and RBS weakening dimensions. The complete dataset provides quantitative support for the derivation of the ultimate rotation prediction formula and the establishment of the simplified M-P-θ coupling model proposed in the main text, and can be used for further comparative verification and extended parametric research by readers.