Progressive collapse resistance of RC beam-column sub-assemblages

Abstract

To investigate the structural resistance of reinforced concrete frames to mitigate progressive collapse, testing was conducted on two simplified RC beam-column sub-assemblages which were designed in accordance with ACI 318-05, with seismic or non-seismic detailing, under middle-column-removal scenarios. The sub-assemblages consisted of a two-span beam, a middle beam-column joint and two column stubs at both ends of the beam. Test results show that under increasing load at the middle beam-column joint, flexural action and compressive arch action are mobilised sequentially, followed by catenary action when the middle joint has undergone large deformations. Plus, the resistance of compressive arch action (with large axial compression in the beam) and catenary action (with axial tension along the beam) is greater than the flexural capacity based on conventional sectional plastic hinge analysis. Detailed information from the embedded strain gauges on longitudinal steel reinforcement along the whole beam was used to shed light on the development of structural mechanisms. Moreover, interaction diagrams of axial forces and bending moments at critical sections, such as joint interfaces and beam ends, were analysed to further illustrate different mechanisms. Finally, the analytical methods to calculate the respective capacities of flexural action and compressive arch action are presented in this paper.