Improvement of progressive collapse resistance for a steel frame system with beam–web opening.

• Tests on a novel principle with kinked reinforced bars are reported. • Specimens include bars with various diameters, kinked heights, and lengths. • Various fracture and failure modes occurred in the connection types. • The kinked height should match the deformation capacity during beam cracking. • The plastic zone range and installation space should be considered for the length. Various disasters may trigger a progressive collapse of frame structures, resulting in a high demand for new preventive structural strategies. Among the strategies adopted, increasing the joint rotation capacity to improve catenary action and forming a second path in the joint area are the most effective. In this study, a novel principle is proposed, in which the web opening is used to meet the rotation capacity, and kinked reinforced bars are installed in the beam–column joint to realize a second path. Experimental and numerical investigations were conducted on a frame substructure with kinked reinforced bars, considering their diameters, kinked heights, and lengths. The deformation capacity, vertical force vs. deformation response, failure mode, and contributions of the flexural and catenary actions on the reinforced bars were evaluated. The test results demonstrate that the kinked reinforced bars in the reduced-web-section connection (RRWS) specimens started to work after the plastic state. Although they had little influence on the flexural action, they were very important to the catenary action. When the kinked height a was less than 2 d , the bearing capacity and ductility of the specimen increased with a , but further increasing the kinked height a beyond 2 d would reduce both the bearing capacity and the ductility. In addition, the failure modes of the specimens were related to whether the plastic hinge was formed first or the reinforced bar had a major role first. Therefore, it is suggested to select the kinked height of the reinforced bar according to the deformation capacity of the beam, and the diameter of the bar as half of the kinked height. [ABSTRACT FROM AUTHOR]