A performance-based design approach for retrofitting regular building frames with steel braces against sudden column loss

Progressive collapse resistance of existing building structures against sudden column loss may be increased with adequate supply of steel braces. A performance-based design approach for retrofitting regular building frames with steel braces is proposed in this study. The retrofit design approach is developed from the pseudo-static response analysis of an idealized elastic–plastic, single degree-of-freedom system. Analytical relationship between the increment of collapse resistance and structural characteristics is derived to determine the design strength and stiffness of added braces. Accuracy of the proposed approach is verified with incremental dynamic analysis. Also, its application to multi-story buildings is demonstrated with three frame models. Conservative performance is obtained with the design approach, especially for a larger resistance increment. An iterative modification technique is suggested to refine the retrofit design and only a few nonlinear static iterations are required for convergence. Nonlinear dynamic analysis results indicate that the column-loss response of the braced frames is approximated to the performance target and thus the proposed retrofit design approach is feasible for practical applications.

► A performance-based retrofit design approach against sudden column loss is proposed.
► Analytical formulations are derived for the design of added braces.
► Conservative structural response is obtained for braced building frames.
► An iterative modification technique is suggested to refine the preliminary design.
► The refined results are consistent with the specified performance target.