Abstract: Taking the beam-through connection in steel frame structures as the research object, two strengthening methods involving the addition of rectangular and curved plates were proposed to enhance the progressive collapse resistance. The collapse resistance capacity, failure modes, deformation patterns and strain development at critical sections of the joint substructures were obtained through experiment. A verified finite element analysis was employed to investigate the effect of the proposed strengthening method and analyze the influence of key parameters. Results demonstrate that the peak load and corresponding displacement of the rectangular plate strengthened substructure are increased by 73% and 42%, respectively, compared with the original structure, while the curved plate strengthened substructure exhibits 102% and 43% enhancements in the peak load and corresponding displacement. The effect of curved plate is superior to that of rectangular plate. The thickness, length and width of rectangular plates have a relatively minor influence on the progressive collapse resistance of the structure. The impact of the thickness and approximate radius of the curved plate is quantified. Two failure modes under the curved plate reinforcement method are identified. Design requirements for the dual fracture failure mode are proposed to fully utilize the material properties of steel beams.