In this paper, four 1/2 scaled precast concrete (PC) beam-column subassemblages with high-performance connection were tested under push-down loading procedure to study the load-resisting mechanism of PC frames subjected to different column removal scenarios. The parameters investigated include the location of column removal and effective prestress in tendons. The test results indicated that the failure modes of unbonded post-tensioned precast concrete (PTPC) frames were different from that of RC frames: No cracks formed in the beams and wide opening formed near the beam to column interfaces. For specimens without overhanging beams, the failure of side column was eccentric compression failure. Moreover, the load-resisting mechanisms in PC frames were significantly different from that of RC frames: The compressive arch action (CAA) that developed in concrete during column removal was mainly due to actively applied precompressive stress in the concrete; CAA will not vanish when severe crush in concrete occurred. Thus, it may provide negative contribution for load resistance when the displacement exceeds one-beam depth; the tensile force that developed in the tendons could provide catenary action from the beginning of the test. Moreover, to deeper understand the behavior of tested specimens, numerical analyses were carried out. The effects of concrete strength, axial compression ratio at side columns, and loading approaches on the behavior of the subassemblages were also investigated based on validated numerical analyses.
Although the first progressive collapse event occurred in precast concrete (PC) buildings due to gas explosions, the behavior of PC buildings resisting progressive collapse is still unclear because related tests are few, and the types of PC connections vary. To study the progressive collapse resistance of monolithic PC beam-column assemblies under a middle column removal scenario, an experimental program including four PC assemblies and one reinforced concrete (RC) assembly is conducted. These PC assemblies contain different types of beam-column connections, including connections of lap-splice, 90° hook anchorage, U-shaped bar, and combined U-shaped bar and 30° hook anchorage. The test results demonstrate that flexural action, compressive arch action (CAA), and catenary action were mobilized in sequence in the beams of RC and PC assemblies. Thus, in general, the development of load resisting mechanisms of PC assemblies is similar to that of RC assemblies, although different types of connections may affect the magnitude of each mechanism. The PC assemblies with 90° hook anchorage and U-shaped bar connections attained a CAA capacity similar to that of the RC assembly, whereas the PC assembly with the combined connections had a greater CAA capacity because of plastic hinge relocation at the beam ends near the middle column. The PC assembly with lap-splice connections achieved the lowest CAA capacity due to the anchorage failure of the beam bottom rebar. However, this PC assembly attained the greatest catenary action capacity, because the beam bottom rebar did not fracture and could still develop tension. Subsequently, an analytical model is proposed to reveal the nature of CAA and to better understand the influence of critical parameters.
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