Experimental Full-Scale Progressive Collapse Test of a 3D Steel-Frame Substructure with RC Slabs

This paper presents an experimental study on the progressive collapse behavior of a full-scale three-dimensional (3D) steel frame substructure with cast-in-place reinforced concrete (RC) floor slabs. A full-scale specimen and relatively large-span RC floor slabs were the two main features of the experimental test. The alternate load path (ALP) method was chosen as the research approach, with one external column being removed before testing. A specially designed 12-point loading system was employed to load the specimen quasi-statically, allowing the acquisition of the load-displacement response and failure process of the test specimen from the initiation of loading to the final collapse. Additionally, based on the test, the deformations of structural members, contributions of various load-resisting mechanisms, load redistribution among the remaining parts of the structure, and dynamic response were analyzed. The ultimate collapse resistance of the structure was theoretically predicted based on the yield line and plastic hinge theories. The test and analysis results led to the following findings: One, the typical steel frame structure in this study, designed based on current steel structure codes, withstood the failure of an external column. Two, tensile membrane action (TMA) primarily developed in the floor slab parallel to the double-span beam above the removed column. Three, flexural action (FA) was the main contributor to resisting the vertical loads throughout the loading process. Its contribution reached up to 88% at the structural ultimate load-carrying capacity position. However, before the final failure of the structure, the loads resisted by catenary action (CA) in beams and TMA in floor slabs could not be ignored. The sum of the two accounted for one-third of the total vertical loads. Four, Columns C1 and C2, directly connected to the removed column through the double-span beam B1-B2, sustained the majority of the vertical loads. Five, for steel frame structures with rigid or semi-rigid connections characterized by good moment resistance but limited rotational capacity, strengthening the connection via additional measures to ensure full development of CA in beams at large deformation stage may be the key to enhancing structural resistance to progressive collapse.