Robustness of Bolted-Angle Connections against Progressive Collapse: Experimental Tests of Beam-Column Joints and Development of Component-Based Models

Several structural collapse incidents indicate that failure usually starts from beam-column joints exposed to abnormal loads, especially for steel and composite structures. If the connections are sufficiently robust and there is adequate axial restraint from adjoining structures, catenary action forms in the beams and slabs, causing alternate load paths when affected columns are severely damaged, and resulting in large deformations in the beams and slabs. This paper presents experimental results of bolted-angle beam-column joints under a middle column-removal scenario. Three types of connectionsincluding (1) web cleat, (2) top and seat angle, and (3) top and seat with web angle connectionswere investigated, and three angle thicknesses (8, 10, and 12 mm) were tested. The results of the nine experimental tests conducted demonstrate the ductility and load-carrying capacities of these three connection types with different angle thicknesses in catenary action mode. When the angle thickness increases, the failure mode changes from angle fracture to bolt fracture. A component-based model is also developed to predict the behavior of bolted-angle beam-column joints up to total failure. The validation study indicates that the proposed models can represent the key responses of bolted-angle beam-column joints under a middle column-removal scenario, including the formation of flexural action at small deformation stage, the development of catenary action at large deformation stage, and fractures of the connection components at the last stage. Based on the proposed joint model, frame analyses are conducted. The analytical results of the frame models demonstrate that the conducted joint tests could represent the behavior of prototype steel frames against progressive collapse. The effect of horizontal restraint stiffness, which is critical to the development of catenary action, is also investigated.