Disproportionate collapse performance of partially restrained steel frames with bolted T-stub connections

Current design and regulatory documents require the assessment of certain buildings with regard to their vulnerability to disproportionate collapse through notional load-bearing element removal followed by an alternative path analysis. While several recent studies have examined the robustness of steel building frames with fully moment-resistant connections and their ability to sustain local damage to load-bearing elements, only limited research is available regarding the robustness of steel frames with partially restrained (PR) connections. This paper investigates the performance of steel frames with partially restrained connections fabricated from bolted T-stubs following damage to load-bearing columns. A macro-model of a bolted T-stub connection for use in nonlinear analysis is presented, verified through experimental data, and incorporated in a nonlinear finite element model to evaluate the performance of PR frames. Two prequalified T-stub connections are considered, one of which is intended to develop the full moment capacity of the beam. The evaluation is conducted for various floor plans of typical office buildings. The analysis indicates that the frames with strong T-stub connections can resist collapse in damage scenarios involving notional removal of one first-story column, while the robustness of the frames with weak T-stub connections is questionable.